Filed under: pictures Tagged: blogging, iPhone, Og

In the thirteenth century, Western Europe rediscovered the teachings of ancient Greece. Two friars played a lead role in this: the Dominican Saint Thomas Aquinas (1225 – 1274) and the Franciscan Roger Bacon (1214/1220 –1292).  Aquinas combined the teaching of Aristotle with Christianity. His teachings became the orthodoxy in both Christianity and natural philosophy until the scientific revolution in the seventeenth century. Aquinas took Aristotle as an authority and, in turn, was taken as an authority by those who followed him. To some extent this has continued down to the present day, at least in the Catholic Church. The scientific revolution was, to a large extent, the overturning of Aristotelian philosophy as repackaged by Aquinas.

Bacon took a different track and extracted something different from the study of Aristotle. This something different was an early version of the scientific method. He applied mathematics to describe observations and advocated using observation to test models. Bacon described a repeating cycle of observation, hypothesis, experimentation, and the need for independent verification.  Bacon was largely ignored and, unlike Aquinas, was not declared a saint. Galileo Galilei (1564 – 1642), if not directly influenced by Bacon, was in many ways following his tradition, both in his use of mathematics and in stressing the importance of observations. The difference between Aquinas and Bacon is the contrast between the appeal to authority and the finding out for oneself. In this contest, the appeal to authority lost rather decisively, but it was a long tough fight. People generally prefer a given answer, even if it is wrong, to the tough process of extracting the correct answer.

In spite of all that, appeal to authority is frequently necessary. The legal system in most democracies, for example, is based on the idea of appeal to authority. The parliament may make the laws but it is the courts that decide on what they mean.  Frequently, the courts even have the authority to override laws based on the constitution. This is true in many countries but most famously in the United States of America. In these countries, what the Supreme Court says, is the law. What a law actually means is commonly a matter of interpretation as evidenced by split decisions where one judge holds one opinion and another judge the opposite. Perhaps the interpretations are even arbitrary as they sometimes change over time despite the authority given to precedence. But a decision is required and there is no objective criteria, so the majority rules.

Now, it is worth commenting that that laws of nature and laws of man are completely different beasts and it is unfortunate that they are given the same name. The so called laws of nature are descriptive. They describe regularities that have been observed in nature.  They have no prescriptive value. In contrast, the laws of man are prescriptive, not descriptive. Certainly, the laws against smoking marijuana are not descriptive in British Columbia, neither were the laws against drinking during US prohibition. The laws describe what the government thinks should happen with prescribed punishments for those who disobey. However, there is no penalty for breaking the law of gravity because, as far as we know, it can’t be done. If someone actually did it, it would cease to be a law and there would be a Nobel Prize, not a penalty.  Like the laws of man, the laws of God—for example, the Ten Commandments—are prescriptive, not descriptive, with penalties given for breaking them. You can break the law of man and the laws of God, but not the laws of physics.

In science, things are different than in the courts of law. In the latter, we are concerned with the meaning of a law that some group of people have written. This, by its very nature, has a subjective component. In science, we are trying to discover regularities in how the universe operates. In this, we have the two objective criteria: parsimony and the ability to make correct predictions for observations. As pointed out in the previous post, idolizing a person is a mistake, even if that person is Isaac Newton. Appeal to observation trumps appeal to a human authority, but in the short term, even in science, appeal to a human authority is often necessary. Life is too short and the amount to know too large to discover it all for oneself. Thus, one relies on authorities. I consult the literature rather than trying to do experiments myself. We consult other people for expertise that we do not have ourselves. We rely on the collective wisdom of the community as reflected in the published literature. When we require decisions, we must rely on the proximate authorities of peers in a process called peer review. This process is relied on to maintain the collective wisdom and will be discussed in more detail in the next post.  In the meantime, we conclude this post by paraphrasing William Lyon McKenzie King[1] (1874 –1950): Appeal to authority if necessary but not necessarily appeal to authority.

Additional posts in this series will appear most Friday afternoons at 3:30 pm Vancouver time. To receive a reminder follow me on Twitter: @musquod.

By Bill Nye Audacious— that's how I describe the Arecibo radio telescope. For me, it was just hard to believe what I was seeing. I have just returned from my first Planetary Society-sponsored trip to Puerto Rico and this historic, remarkable, big idea of a telescope. The Arecibo Radio TelescopeCredit: The Planetary Society If you're not familiar with this machine designed to explore the cosmos and our own ionosphere, it was conceived in ....

It's been a little while since I wrote up what I've been doing in my "Brief History of Timekeeping" class, because I was out of town, and then catching up from being out of town. Some of this material has already appeared here, though, so I can hopefully catch up a lot of stuff in one post.

The material that will be most interesting to random readers of the blog is the "How to" section, from a couple of weeks ago, which were the lecture form of the How to Read a Scientific Paper and How to Present Scientific Data posts here. The paper-reading class was on Monday and the data-presentation class on Friday, with a class going through a particular paper on The mechanics of the sandglass sandwiched in between. This also served as the explanation of the working of sand timers, one of our historical timekeeping technologies.

The next week was shortened because I was out of town for the weekend, and introduced mechanical clocks. I started off with this video clip from Connections, which provides a very nice illustration of early mechanical clocks:

Also, you could land an airplane on the lapels of that jacket. As I told the students, I'm just barely old enough to remember the brief moment when that didn't look ridiculous.<.p> Read the rest of this post... | Read the comments on this post...

Last night, researchers and public health officials gathered high above New York City’s ‘Ground Zero’ in hopes of narrowing the divide within the scientific community over the fate of two papers currently in the press at Nature and Science demonstrating mammalian transmission of avian influenza H5N1. Dozens of commentaries and news stories have born out the debate as to whether or not the research should be published in full, allowing others to replicate it. Michael Osterholm, who was part of the National Science Advisory Board for Biosecurity (NSABB) which unanimously recommended redaction of the papers, referred to them as, “the two most famous unpublished manuscripts in the history of life science.”

At the panel, hosted by The New York Academy of Science, moderator W. Ian Lipkin of Columbia University said that “the emotional debate is something we’re going to try to keep to a low roar tonight.” Emotions nevertheless ran high as panelists accused each other of misrepresenting facts and rushing too quickly to either publish or censor scientific data.

Nature news arranged for video interviews with several of the panelists prior to the event and we will post these to our website shortly.

Scientific debates erupted about the mortality rate of H5N1, generally known only to transmit from birds to humans. Peter Palese, a virologist at Mount Sinai School of Medicine in New York says that underestimates of the prevalence in the general population have led to an exaggeration as to how deadly H5N1 is. It’s often said to kill 60% of those infected (the deadly ‘Spanish flu’ epidemic of 1918, by comparison, had a 2% mortality rate). Palese recently published an article exploring why this may be an exaggeration.  Osterholm contended that Palese was being selective about the literature he cited but added that even if the death rate was an order of magnitude less than 60%, accidental or purposeful release of mutant H5N1 still frightened him, more than the release of smallpox or Ebola viruses.

A circular argument about animal experiments also ensued. Ferrets, which were used to develop the new form of H5N1, are a common model for mammalian transmission. Palese and Vincent Racaniello of Columbia University, argued that the experiments proving mammalian transmission in ferrets don’t necessarily prove a danger for humans. Ferrets have limitations and aren’t perfectly predictive of how the virus might spread between humans. Laurie Garrett of the Council on Foreign Relations said that this undermines the justification for the work in the first place. “If they do not have predictive value for human beings, then I don’t understand why the experiment was done.”

Barbara Jasny, deputy editor for Science and Véronique Kiermer, executive editor for Nature both appeared willing to accept that the papers will likely be published without the full information necessary to replicate the findings, and argued that there was significant value in doing so. Still, equitably sharing more detailed information with reputable scientists who request it poses a significant challenge that has not quite been worked out. They also recognized the danger in the precedent that redacted publication presents. “I hope this is not something that becomes institutionalized,” says Jasny.

Palese argued that members of the NSABB were being too cautious in recommending only partial publication of the results. “You can always assume the worst. I mean pigs can fly.  But I think all the evidence we have right now doesn’t suggest that these H5N1 viruses can be easily transmitted in humans,” he said. “Where do you stop in terms of being afraid”

Osterholm offered an impassioned response. “I sit here with some emotion when I say this: Dammit, this is a real possibility and if we are wrong the consequences will be so catastrophic that we will all go back and ask ourselves, ‘Why did it happen?’”

But perhaps the biggest theme at the panel was an argument about how involved the public and government bodies can and should be in discussing the fate of these papers and others like them. Garret said that the proliferation of do-it-yourself biology hobbyists and striking differences internationally as to how this work has currently been accepted,  a discussion with all stakeholders including the public was necessary: “You have to have your ears open to a broader range of society than just the people who look through microscopes,” said Garrett.

The NYAS meeting called “Dual-Use Research: H5N1 and Beyond” was open to the public and may be making a recording of it available. Stay tuned.

As a young student, I was taught that mathematics is the language of physics. While largely true, one also cannot communicate in CMS at the CERN LHC without learning a plethora of acronyms. When we wrote the CMS Trigger and Data Acquistion System (TriDAS) Technical Design Report (TDR) in year 2000, we included an appendix that contained a dictionary of 203 acronyms from ADC to ZCD, quite necessary to digest this document.  In the next years, the list of acronyms would grow exponentially. We even have nested acronyms, LPC, for example standing for LHC Physics Center. In a talk of many years ago, one of my distinguished collaborators flashed a clever new creation and quipped “I believe this is the first use of a triply-nested acronym in CMS.” I do not know if since then we have reached  quads or quints. Somehow it would not surprise me.

One of the latest creations is YETS: Year End Technical Stop, referring to the period between the end of the heavy ion run on 7 December 2011 and the restart of LHC operations due to begin next week with hardware commissioning leading ultimately to pp collisions in April. So what to physicists do during YETS? A lot as it turns out!

One of the major activities is how to cope with the projected instantaneous luminosity of 7e33 (per cm**2 per s). This luminosity will likely come with a 50 nanosecond beam structure (the time between collisions) as was used in 2011. This means that the average number of pp interactions per triggered readout will be about 35, the one you tried to select with the trigger, plus many more piled on top of it. This affects trigger rates and thresholds, background conditions, and the algorithms used in the physics analysis. In addition, we shall likely run at 8 TeV total energy (compared to 7 last year). These new expected conditions are being simulated, a process requiring a huge amount of physicist manpower and computing resources. The results are carefully scrutinized in collaboration-wide meetings. That is the “glory” activity.

Besides the glory work, there is also a huge amount of technical service work, both hardware and software. At CMS in Point 5 (P5) we have observed beam-induced pressure spikes (rise and fall) in the vacuum. The pumping required for recovery is using up the supply of non evaporable getter (NEG) needed to achieve ultrahigh vacuum (UHV). The UHV in turn is needed to ensure that the beams do not abort which nearly happened last year. A huge effort was launched to radiograph the region in question to see if the same problems of drooping radio frequency (RF) fingers are present as has been observed in other sectors. An electrical discharge from the RF fingers can possibly cause the UHV spikes. Also at P5 work will be done on the zero degree calorimeter (ZDC), the Centauro And Strange Object Research (CASTOR) detector (not to be confused with CERN Advanced Storage Manager), the cathode strip chamber (CSC), the restive plate chamber (RPC) and the drift tube (DT) muon detectors which are accessible without opening the yoke of CMS. In addition, there is maintenance of the water cooling and rewiring of the magnet circuit breaker.

Each of the CMS subsystems has work to do as evident by a recent a trip into the P5 pit. The detailed activities of the pixel (PX), silicon tracker (TK), electromagnetic calorimeter (ECAL), and muon (MU) subdetectors are beyond the scope of this blog. I can give you some idea of what is going on with the hadron calorimeter (HCAL), where a bit of the details are fresh in my mind.

The HCAL activities are quite intense. Detector channel-by-channel gains, the numbers that are needed to convert electrical signals into absolute energy units can vary with time for a variety of reasons (e.g. radiation damage) and need periodic updating. This information has to go into the look up tables (LUTs) that are used by the electronics to provide TPGs (trigger primitive generation) which are in turn used by the level-1 hardware trigger to select events. If these numbers in the LUTs are slightly off, then the energy threshold that we think we are selecting is off target which is very bad because trigger rates vary exponentially with energy.

The HCAL uses 32 optical S-LINKs (where the S stands for simple, although I don’t remember anything simple about getting it to work) to send the data to DAQ computers. My group at Boston designed and built the front end driver (FED) electronics that collects and transmits the data on these links. The data transmission involves a complex buffering and feedback system so that the data flow can be throttled without crashing in case something goes wrong. The data flow reached its design value of 2 kBytes per link per event at the end of 2011 so we are going to reduce the payload by eliminating some redundant data bits which were previously useful for commissioning the detector but are no longer needed. This will allow us to comfortably handle the expected increase in event size due to increased pileup. Also 4 of our boards developed dynamic random access memory (DRAM) problems after a sudden power failure which took up two days of my time at CERN to inventory spares, isolate the affected DRAMS, and arrange for repairs.

The HCAL computers at P5 are running 32 bit Scientific Linux CERN (SLC4, another nested acronym). While we enjoyed the stability of this release over a number of years, it will no longer be supported by CERN after February 2012.  These computers are being upgraded (as I write this!) to 64 bit SLC5.

The HF calorimeters will have their photomultiplier tubes (PMTs) replaced in the LS1. We would like to do measurements with a few new PMTs in order to study performance stability and aging in the colliding beam environment. This activity requires building and testing new high-voltage (HV) distribution printed circuit boards (PCBs). The HV PCBs require testing and installation in the current HF read out boxes (ROBOXs) while there is still access to the detector.

Our group at Boston in also involved with designing electronics needed for the HCAL upgrade, the first part of which will take place in the first long shutdown (LS1). The new electronics is based on micro telecommunications computing architecture (uTCA). In Boston we have built a uTCA advanced mezzanine card for the unique slot number 13 (AMC13). This card will distribute the LHC clock signals needed for trigger timing and control (TTC) as well as serve as the FED. We plan to test these cards during the 2012 run. To prepare for these tests we have installed an AMC13 card in the central DAQ (cDAQ) lab which can transmit data on optical fibers to a multi optical link (MOL) card which exists in the form of a personal computer interface (PCI) card that can be readily attached to a computer. I addition, to be able to perform the readout tests with the new electronics without interrupting the physics data flow, we have installed optical splitters on the HCAL front end digital signals for a portion of the detector, parts of the HCAL barrel (HB), HCAL end cap (HE), and HCAL forward (HF), so that one path can be used for physics data and the other path for uTCA tests.

I can assure you that the activities in parts of CMS are (almost) as intense as during physics runs. There has been a lot to do!

I once met a secretary in California, the land of innovative thinkers, who was exposed to physics through typing exams, that could not understand why students thought physics was so hard. She thought each letter always stood for the same thing and once you learned them you were pretty much set. I am not sure she believed me when I told her there weren’t enough letters to go around. Same thing with acronyms. A quick search for CMS will include: Center for Medicare & Medicaid Services (a nested acronym), Content Management System, Chicago Manual of Style, Chronic Mountain Sickness, Central Middle School, City Montessori School, Charlotte Motor Speedway, Comparative Media Studies, Central Management Services, Convention on Migratory Species, Correctional Medical Services, College Music Society, Colorado Medical Society, Cytoplasmic Male Sterility, Certified Master Safecracker, Cryptographic Message Syntax, Code Morphing Software, Council for the Mathematical Sciences, Court of Master Sommeliers, and my own favorite, a neighborhood landscaper Chris Mark & Sons, of which am proud owner of one of their shirts.

And for those against acronym abuse, you can buy an AAAAA T-shirt (maybe I will too):

Thanks to Kathryn Grim for suggesting a blog about what goes on at an LHC experiment during shutdown.

 

NASA has the blessing of a committee of US astronomers to become a small-percentage partner in Euclid, a European Space Agency (ESA) mission to study dark energy.

The National Academies issued a short report today endorsing a deal where $20 million from NASA would buy access to Euclid data for US astronomers.

NASA has been trying to find a way to study dark energy — the anti-gravitational stuff that’s accelerating the expansion of the Universe — with a small space telescope for years. Initially that was to be JDEM, a joint mission with the US Department of Energy that was also to have ESA involvement. But that ménage-à-trois fell apart: the DOE withdrew its support while ESA and NASA pushed ahead on independent proposals, Euclid, and WFIRST, respectively.

But because the James Webb Space Telescope is hogging the money in NASA’s astrophysics division, Euclid will fly before WFIRST — if WFIRST flies at all. And NASA didn’t want to get left behind.

The $20 million contribution is likely to come in the form of infrared detectors. That contribution gets US representation on the science team, and also gets about 20 scientists early access to Euclid data, says David Spergel of Princeton University in New Jersey, who chaired the Academy report. For a contribution of just a few percent of the overall mission costs, NASA would be getting something like 10% of the control and access to data, Spergel says. “It’s a good deal,” he says.

Why was NASA tiptoeing around such an apparent no-brainer? Because NASA had also tried to be a 20% partner in Euclid — and the US astronomy community rose up in protest, in the form of another Academy report, which in December 2010 said that such a large partnership violated the recommendations of the astronomy decadal survey and might damage WFIRST’s chances. “We still think it’s essential to move forward with WFIRST,” says Spergel. Euclid could launch as soon as 2018.

Image credit: ESA

This is so cool: NASA’s twin GRAIL spacecraft (now named Ebb and Flow) have cameras on board to take images of the lunar surface, and an animation has been put together of Ebb’s view of the Moon’s far side!

Pretty neat. I love the wide-angle view; the individual images were taken while Ebb was still over a thousand kilometers from the Moon. The huge circular feature you can see on the right 30 seconds into the video is Orientale Basin, an impact so huge it must’ve lit up the solar system a few billion years ago. That basin is nearly 1000 km (600 miles) across! See the LRO image below for a clearer view, and click it for more info.

I’m really looking forward to seeing what will be done with these cameras. As Principal Investigator Maria Zuber explains in the video, they were installed specifically for educational purposes, and kids all over America will get a chance to examine the data. I love this idea, since it means these children will be invested in the project itself, and remember it for their whole lives. It’s a fantastic idea.

Image credit: NASA/GSFC/Arizona State University

Patrick Donohue is a fourth-year Ph.D. student working with Clive Neal at the University of Notre Dame, whose primary research focus is on the origin and evolution of high-titanium lunar basalts. He writes a geology blog and is active on Twitter under the username poikiloblastic. He's also an amateur photographer, shooting sports, and wildlife, and of course interesting geology! The following is the first in a series of posts based on field ....

For CMS data analysis, winter is a time of multitasking. On the one hand, we are rushing to finish our analyses for the winter conferences in February and March, or to finalize the papers on analyses we presented in December. On the other, we are working to prepare to take data in 2012. Although the final decisions about the LHC running conditions for 2012 haven’t been made yet, we have to be prepared both for an increase in beam energy and an increase in luminosity. For example, the energy might go to 8 TeV center-of-mass, up from last year’s 7. That will make all our events a little more exciting. But it’s the luminosity that determines how many events we get, and thus how much physics we can do in a year. For example, if the Higgs boson exists, the number of Higgs-like events we’ll see will go up, and so will the statistical power with which we can claim to have observed it. If the hints we saw at 125 GeV in December are right, our ability to be sure of its existence this year depends on collecting several times more events in 2012 than we got in 2011.

We’d many more events over 2012 if the LHC simply kept running the way it already was at the end of the year. That’s because for most of the year, the luminosity was increasing over and over as the LHC folks added more proton bunches and focused them better. But we expect that the LHC will do better, starting close to last year’s peak, and then pushing to ever-higher luminosities. The worst-case we are preparing for is perhaps twice as much luminosity as we had at the end of last year.

But wait, why did I say “worst-case”?

Well, actually, it will give us the most interesting events we can get and the best shot at officially finding the Higgs this year. But increased luminosity also gives more events in every bunch crossing, most of which are boring, and most of which get in the way. This makes it a real challenge to prepare for 2012 if you’re working on the trigger, because have to sift quickly through events with more and more extra stuff (called “pileup”). As it happens, that’s exactly what I’m working on.

Let me explain a bit more of the challenge. One of the triggers I’m becoming responsible for is trying to find collisions containing a Higgs decaying to a bottom quark and anti-bottom quark and a W boson decaying to an electron and neutrino. If we just look for an electron — the easiest thing to trigger on — then we get too many events. The easy choice is to ask only for higher-energy electrons, but beyond a certain points we start missing the events we’re looking for! So instead, we ask for the other things in the event: the two jets from the Higgs, and the missing energy from the invisible neutrino. But now, with more and more extra collisions, we have random jets added in, and random fluctuations that contribute to the missing energy. We are more and more likely to get the extra jets and missing energy we ask for even though there isn’t much missing energy or a “Higgs-like” pair of jets in the core event! As a result, the event rate for the trigger we want can become too high.

How do we deal with this? Well, there are a few choices:

1. Increase the amount of momentum required for the electron (again!)
2. Increase the amount of missing energy required
3. Increase the minimum energy of the jets being required
4. Get smarter about how you count jets, by trying to be sure that they come from the main collision rather than one of the extras
5. Check specifically if the jets come from bottom quarks
6. Find some way to allocate more bandwidth to the trigger

There’s a cost for every option. Increasing energies means we lose some events we might have wanted to collect — which means that even though the LHC has produced more Higgs bosons, it’s counterbalanced by us seeing fewer of the ones that were there. Being “smarter” about the jets means more time spent by our trigger processing software on this trigger, when it has lots of other things to look at. Asking for bottom quarks not only takes more processing, it also means the trigger can’t be shared with as many other analyses. And allocating more bandwidth means we’d have to delay processing or cut elsewhere.

And for all the options, there’s simply more work. But we have to deal with the potential for extra collisions as well as we can. In the end, the LHC collecting much more data is really the best-case scenerio.

Not much to say, but I would like to mention that, finally, we have been able two finalize two write-ups that I have announced here in the past:

First, there are the notes of a block course that I have in the summer on how to fix some mathematicla lose ends in QFT (notes written by our students Mario Flory and Constantin Sluka):

How I Learned to Stop Worrying and Love QFT

Lecture notes of a block course explaining why quantum field theory might be in a better mathematical state than one gets the impression from the typical introduction to the topic. It is explained how to make sense of a perturbative expansion that fails to converge and how to express Feynman loop integrals and their renormalization using the language of distribtions rather than divergent, ill-defined integrals.

Then there are the contributions to a seminar on "Foundations of Quantum Mechanics" (including an introduction by your's truly) that I taught a year ago. From the contents:

1. C*-algebras, GNS-construction, states, (Sebastian)
2. Stone-von-Neumann Theorem (Dennis)
3. Pure Operations, POVMs (Mario)
4. Measurement Problem (Anupam, David)
5. EPR and Entanglement, Bell's Theorem, Kochen–Specker theorem (Isabel, Matthias)
6. Decoherence (Kostas, Cosmas)
7. Pointer Basis (Greeks again)
8. Consistent Histories (Hao)
9. Many Worlds (Max)
10. Bohmian Interpretation (Henry, Franz)

Posted on behalf of Michele Catanzaro.

Omid Kokabee, a physics student accused of spying by Iran, has spent one year in Evin jail in Tehran without being judged. In a hearing on 31 January the trial was postponed for at least another four months, according to sources in Tehran. The trial has already been postponed twice before, in July and October.

Kokabee complains in an open letter published by the opposition magazine Khaleme that authorities are trying to obtain his “collaboration” through threats to him and his family. According to this document, Iranian authorities are seeking scientific cooperation: “My only mistake has been to study and seek expertise in a field that has turned out to be needed,” the document states.

Kokabee, a 29-year-old Iranian graduate student in laser physics at the University of Texas, Austin, was arrested by Iranian intelligence at Tehran’s airport in February 2011, and accused of “collaboration with a hostile government” and “illegal earnings”. In an earlier open letter, published by Kaleme in July, he proclaimed his innocence, and the American Physical Society, along with four international optics organizations, asked for a fair trial for him.

The Committee of Concerned Scientists, which started a petition demanding a fair trial, will discuss Kokabee’s case at its Annual Board Meeting on 19 February “with two distinguished guests from Iran”, says Eugene Chudnovsky, the organization’s co-chairman. “At that time decisions will be made on how to address Omid’s case in the most effective way.”

There is just something wonderful when Hubble points to nearby spiral galaxies. Sprawling and detailed, we get both great resolution on smaller features as well as a jaw-dropping overview of a grand spiral… like, say, NGC 1073:

Yeah, I know. [Click to galactinate -- I had to shrink it to fit here, and it lost a lot of the coolness when I did -- or grab the 3900 x 3000 pixel version.]

NGC 1073 is a decent-sized spiral galaxy about 60 million light years away. It’s actually part of a small, tight group of galaxies many of which are far more famous (like NGC 1068). But 1073 is important because of a simple property: it looks like us.

While it’s not a perfect match, NGC 1073 does bear an interesting resemblance to our Milky Way galaxy (UGC 12158 looks more like our galaxy, but is far bigger, for example). Both have large, rectangular bars going across their centers. Bars are a bit odd, since you’d expect the arms just to wind all the way down to the center. But the gravity of a galaxy isn’t like the gravity of a solar system, with a big heavy star sitting in the center. Galaxies have their mass spread out over a long distance, so what gas and dust clouds and stars feel in the way of gravity is different, and bars are a natural outcome of that. However, they’re still not perfectly understood. Bars may form when galaxies collide, and they might be an indication of a galaxy reaching middle age. Perhaps there are other factors as well.

Studying galaxies like NGC 1073 will help us understand how bars form, and why we have one too. Remember, we’re stuck inside our galaxy and can’t see it from the outside (that picture above is an illustration based on detailed observations). It really helps our understanding of the Milky Way to observe galaxies like ours.

An important thing too is that the two galaxies are different in some ways: NGC 1073 has more open arms, for example, compared to our more tightly wound arms. Those differences are telling us something as well. What is it that makes one galaxy hold its arms closer in, and another to fling them out? Why does this galaxy have two arms, and that one three? If you can look at two galaxies that are alike except in one way, it’s easier to isolate the cause. So studying NGC 1073 is a great way to study ourselves.

It always makes me think of Nietzsche, who wrote on the nature of man, "And when you gaze long into an abyss, the abyss also gazes into you."

But on the nature of the Universe, it changes: "And when you gaze long into an abyss, your gaze falls back on yourself."

---

Related posts:

- The Milky Way’s (almost) identical twin
- Barred for life
- Unwind with some spirals
- Setting the bar
- Sculpting a barred galaxy

By Matin Durrani
My eye was caught this morning by a new report from the Institute of Physics, which publishes physicsworld.com, about the number of physicists at UK universities.

Entitled Academic Physics Staff in UK Higher Education Institutions, you can read the full report here, but what I found particularly interesting were the data on women in physics.

The report reveals that the proportion of staff in UK physics departments who are women has risen steadily from 13% in 2003/04 to 16% in 2009/10. (See figure above: data in it are from the UK's Higher Education Statistics Agency.)

As one might expect, the biggest rises are at more junior levels, with the proportion of female lecturers going up from 11.3% to 19.8% over that period. Senior-lecturer numbers have increased from 9.0% to 11.2% and although the proportion of female professors has risen form 3.9% to 5.5%, women in these top positions are still very much in the minority.

Given that women make up about 22% of UK physics undergraduates, is it too much to hope that in 15 or 20 years' time women will also make up a fifth or so of physics professors?

Another intriguing statistic concerns the highly international level of UK physics, particularly among women. According to the report, the proportion of female staff at UK universities who are not from the UK has risen from 46% in 2003/04 to 51% in 2009/10. This is much higher than the fraction of male non-UK nationals at UK universities, which has gone up from 31% to 40% in the same period.

Overall, across both men and women, the biggest proportion of non-UK staff working in UK physics departments come from Germany, followed by Italy, the US, China, Russia, France, India, Greece and the Netherlands. Make of that what you will.

You can read the full report here.

• Whither The Occupation - Ta-Nehisi Coates - National - The Atlantic

  "There's an argument that the process of federal legislation, at this point, is crippled by deep systemic problems. The filibuster is an obvious example. It's also worth pointing out that there is a space for activism beyond electoral politics. But laws exist for a very good reason. They are--roughly put--a compact between citizens and the state detailing the guidelines for governance. Laws--and their alteration or abolishment--are the means by which we change the compact. The alternative, to my mind, is revolution. At the end of the piece Greenberg notes that the leadership is seeking to emulate the Civil Rights movement of the 60s. I hope no one told him that directly. If they did, Occupy reflects a poor understanding of that movement's lessons. The Civil Rights movement neither eschewed the hard work of mapping out concrete goals, nor shied away from changing laws."

• slacktivist » Groundhog Day and the 10,000-hour montage

  When I first encountered this idea of virtue as craft, I found it exciting and even liberating because it was so different from the idea of virtue I had learned growing up in American fundamentalist Christianity. I had been taught to think of virtue as mainly a matter of avoiding sin -- of abstaining from a long list of bad things. Virtue wasn't something to do, but something you had because of all the things you didn't do. It wasn't a craft to be learned, developed and practiced, but a stockpile to be safeguarded and hoarded. It was as though we had each been given an initial supply when we were born again as innocents, and that finite supply had to be preserved, clasped tightly, and kept pure from a dangerous and poisonous world. The best that one could hope for, in such a view, was that 10,000 hours later one might have vigilantly defended and retained most of one's original purity so that one wasn't any worse after all that time.

• Frequency comb reaches extreme ultraviolet - physicsworld.com

  Physicists in the US have created an optical frequency comb that operates in the extreme ultraviolet (XUV). Touted as the first practical comb to work in this region of the spectrum, the device could be used to look for tiny variations in the fine-structure constant and other physical constants that could point to new physics. An XUV comb could also be used to create better atomic clocks and new techniques for atomic spectroscopy.

Read the comments on this post...

We’re currently enduring a spell of cold weather here in Cardiff, although I think it might be rather milder here then elsewhere in the UK. My garden thermometer showed a mere -5 C when I looked at it at 7.15 this morning. The other day we had a meeting of half-a-dozen people in one of our large teaching rooms and it was absolutely freezing. I don’t know what was wrong with the heating. Yesterday I actually did a lecture in the same room, but with 80-odd “warm bodies” (or “students” as they are sometimes known) in there, it was bearable.

The cold here of course is nothing compared with that endured by Captain Scott‘s ill-fated expedition to the South Pole, but I mention it here for a number of reasons. First, the centenary of the death of Scott and his companions is coming up next month; the tragedy unfolded in March 1912. There’s actually a very special concert coming up next week, featuring Vaughan Williams’ wonderful music written for the classic film Scott of the Antarctic (which, incidentally, you can actually watch in full on Youtube). I’m definitely going along, and will probably review the performance next week, but quite a number of my colleagues are also going, for reasons which will become obvious..

The concert is special because of the very strong connections between the Scott Expedition and the City of Cardiff. Much of the financial support needed to fund the trek to the South Pole was raised from Cardiff businessmen and Scott’s ship, the Terra Nova, actually set sail from Cardiff (in June 1910) on its journey, first to New Zealand and thence to Antarctica.

Incidentally, an article in this morning’s Western Mail relates to a historic painting of the departure of the Terra Nova which is about to be auctioned:

Cardiff Bay has certainly changed a great deal since 1910, but quite a lot is recognizable, especially the Pierhead Building, which can be seen to the right. The actual docks, the locations of which are revealed by the lines of masts of tall ships, are now mainly filled in. But there is at least one other reminder of this occasion to be found at Cardiff Bay, a large waterfront bar itself called Terra Nova…

There’s also a deep connection with the South Pole, and the Antarctic generally, for many members of the Astronomy Instrumentation Group here in the School of Physics & Astronomy at Cardiff University, quite a few of whom have actually been to the South Pole in connection with various experiments, including Quad,  Boomerang and BLAST, because of the unique observing conditions there.

Follow @telescoper

As the ABC PhD course at CREST is about to start (!), I am thinking of setting a few on-line papers to read. Since the most specific topic is ABC convergence, here is the reading list:

• Blum M.G.B. (2010) Approximate Bayesian Computation: a nonparametric perspective. Journal of the American Statistical Association, 105: 1178-1187
• Dean, T.A., Sumeetpal, Singh S.S., Jasra, A. and Peters, G.W. (2010) Parameter Estimation for Hidden Markov Models with Intractable Likelihoods. Cambridge University Engineering Department Technical Report 66,  arXiv:1103.5399v1
• Fearnhead, P. and Prangle, D. (2012) Constructing summary statistics for approximate Bayesian computation: semi-automatic approximate Bayesian computation. J. Royal Statistical Society (Series B)
• Marin, J.-M., Pillai, N., Robert, C.P. and Rousseau, J. (2011) Relevant statistics for Bayesian model choice. arXiv:1110.4700
• Robert, C.P., Cornuet, J.-M., Marin, J.-M. and  Pillai, N.S. (2011) Lack of confidence in approximate Bayesian computational (ABC) model choice. PNAS (Open Access). 108(37), 15112-15117, arXiv:1102.4432
• Wilkinson, R. (2008) Approximate Bayesian computation (ABC) gives exact results under the assumption of model error. arXiv:0811.3355

Filed under: pictures, Statistics, University life Tagged: ABC, CREST, Paris, PhD course, reading list

The Fifth Physics and Society Forum will take place at CERN from 28 to 29 March 2012. 
The purpose of the meeting is to explore the challenges experienced by physicists who leave their field of study to pursue alternative careers in the market place outside of teaching and university-based research. 
   It is widely recognized that a knowledgeable society is a prerequisite for growth. Value is only created if knowledge can be transformed into know-how and "know-how-to-do". Today it is widely recognized that a society is unable to grow and sustain an advanced science system unless equally advanced production is present. Today production is off-shored to emerging economies in Asia and elsewhere where labour costs are more favourable. European physicists therefore have the choice of being smarter, working harder and working cheaper or moving into other fields. 

 Registration is open until 1st March 2012. Please note that special registration fees have been negotiated for CERN employees. For further information about registration, click here.

Coffee Morning Tuesday 7th February 2012, 9:00 – 11:00 Bldg 504 (Restaurant n°2 – DSR) 1st Floor, Club Room 3 Presentation of cheque to Terre des Hommes Those interested in helping should come along. New arrivals and all members are cordially invited.You can enrol for membership, renew membership, find out about and sign up for our activities. Visit our website: http://club-womensclub.web.cern.ch/Club-WomensClub/

Just so you know, I also have felt the biological urge to reproduce. What you see above is myself holding the newest addition to my family. It’s a boy!

In the language of physics this is definitely a phase transition in my lifestyle.  And in spite of the warnings about how much work raising children is supposed to be, it is still more than what I imagined. Nevertheless, my wife and I are very happy. We are also very tired at the moment.

 

Finally, this new human explains some of the silence on this blog at the end of last year and more recently. Once sleep resumes I think I will be back to writing posts more often. I also hope to get some research done in the near future, but everything is taking 3-4 times as long than what it used to.

 

 

 

Filed under: Personal

My Paris colleague (and fellow-runner) Aurélien Garivier has produced an interesting comparison of 4 (or 6 if you consider scilab and octave as different from matlab) computer languages in terms of speed for producing the MLE in a hidden Markov model, using EM and the Baum-Welch algorithms. His conclusions are that

• matlab is a lot faster than R and python, especially when vectorization is important : this is why the difference is spectacular on filtering/smoothing, not so much on the creation of the sample;
• octave is a good matlab emulator, if no special attention is payed to execution speed…;
• scilab appears as a credible, efficient alternative to matlab;
• still, C is a lot faster; the inefficiency of matlab in loops is well-known, and clearly shown in the creation of the sample.

(In this implementation, R is “only” three times slower than matlab, so this is not so damning…) All the codes are available and you are free to make suggestions to improve the speed of of your favourite language!

Filed under: R, Running, Statistics, University life Tagged: Baum-Welch algorithm, C, EM, HMM, Matlab, Octave, Python, R, Scilab, speed

This weekend is SpaceUp unconference in San Diego, and I'll be attending on Saturday. I've never been to an unconference before, so I'm very curious to see how it all works! You can still register if you want to attend, but if you can't, some part of the unconference will be webcast on Spacevidcast. As per the unconference format, there is no set agenda yet, except for Saturday evening from 7:00 to 9:00 p.m. Pacifc, when there will be a ....

JPL issued a news note today with that most dreaded of press release titles: "Mission Status Report," which I dread because it's usually a euphemism for "something bad has happened to one of our spacecraft." But this time it contains nothing but good news. It briefly notes that the Jupiter-bound Juno spacecraft has successfully completed the first of twelve trajectory correction maneuvers it'll perform between launch last year and Jupiter ....

Fraser Cain has organized a weekly Space Hangout that happens at 1800 UTC on Thursdays, and kindly invited me to participate. This week's lineup included him and me as well as Pamela Gay, Nicole Gugliucci, Alan Boyle, and Ian O'Neill. In this week's space hangout, we talked about the search for super earths, the non-discovery of life on Venus, new images from the far side of the Moon, nature versus nurture in star formation, and the tests of ....

One must have a mind of winter
To regard the frost and the boughs
Of the pine-trees crusted with snow;

And have been cold a long time
To behold the junipers shagged with ice,
The spruces rough in the distant glitter

Of the January sun; and not to think
Of any misery in the sound of the wind,
In the sound of a few leaves,

Which is the sound of the land
Full of the same wind
That is blowing in the same bare place

For the listener, who listens in the snow,
And, nothing himself, beholds
Nothing that is not there and the nothing that is.

by Wallace Stevens  (1879-1955).

Follow @telescoper

[Note: Every week I hold a live video chat on Google+ where I answer questions from readers. I call it Q&BA, and when I get a question that stands alone, I'll make it its own video. ]

Every now and again, I hear this urban legend that pound for pound, the human body is actually hotter (or has more energy) than the Sun. I got this question in a recent Q&BA video chat session, so I tackled it. The answer is pretty interesting, and depends on how you ask the question!

I actually wrote about this legend on the blog a while back, and I show all the math. I really like this question, since it has a straightforward answer that makes it seem wrong, but then if you look at it more carefully the answer is a little trickier. And even in the video and that other post, it’s not really a complete answer; if you read the comments on the post you’ll see people arguing over it.

That’s really the best kind of question: the ones that keep on going! There’s always more stuff to figure out.

Visit the Q&BA Archive to see more videos like this one!

The online initiative to boycott the Elsevier publishing company is gaining momentum. For particle theorists, signing to it does not take much. In our community, publishing in Elsevier has been considered, since several years already, on the same footing as farting at the dinner table: technically not forbidden, but somewhat disqualifying. It is heartening that this notion is now spilling outside our little world into large areas of mathematics, physics, and biology. This offers a realistic prospect for a change.

For those born yesterday, we resent Elsevier for:

• charging exorbitant prices,
  
• bundling their offer into all-or-nothing packages,
  
• supporting SOPA/PIPA/RWA to the end of restricting freedom of information.
  

This adds up to the past record of setting up fake-peer-review medical journal, keeping the Chaos, Solitons and Fractals sham far too long, legal bullying, and supporting arms trade. Based on that list, you might object to the boycott by arguing that Elsevier is not infinitely more evil than an average publishing company. That's true, however, I personally view it as only a first step to reforming scientific publishing. Scientists, although modern in many respects, got entangled in a completely anachronic and very inefficient system of distribution and evaluation of their output. This could and should be changed. So, hitting Elsevier would be a largely symbolic move, akin to the storming of the Bastille. Once awareness is raised, it'll be time to march on Versaille and really change the balance of power.

As a particle physics blogger I should sadly note the LHC collaborations have been regularly publishing in Elsevier owned journals such as Physics Letters, Nuclear Physics, or Nuclear Instruments. I guess it's not purposely evil but simply inertia. So if you're an LHC experimentalist, please sign the pledge, and next time someone tries to submit to Elsevier please kick and scream; in case it doesn't help you may consider withdrawing your name from the publication. If the LHC could officially join the boycott, it would be a huge PR push for the initiative.

For further reading, see the posts of Tim Gowers, John Baez, Sean. And let's hope my historical analogy won't extend all the way to guillotining ;-)

In accordance with the Status Agreements with CERN, Switzerland and France facilitate the entry of members of the Organization’s personnel on to their territories.  Where relevant, detailed procedures for obtaining visas apply.

Within the framework of those procedures, only the following individuals are authorised to initiate the note verbale procedure as well as to sign the Official Invitation Letters and the Conventions d’accueil.

1. Kirsti ASPOLA (PH – CMO)
2. Oliver BRÜNING (BE – ABP)
3. Michelle CONNOR (PH – AGS)
4. Patrick FASSNACHT (PH-ADO)
5. David FOSTER (IT – DI)
6. Nathalie GRÜB (PH – AGS)
7. Tjitske KEHRER (DG-DI)
8. Tadeusz KURTYKA (DG – PRJ)
9. Markus NORDBERG (PH – ADO)
10. Cécile NOELS (DG – PRJ)
11. Maria QUINTAS (HR – SPS)
12. Kate RICHARDSON (PH-AGS)
13. Jeanne ROSTANT (PH – AGS)
14. José SALICIO-DIEZ (PH – AGS)
15. Ulla TIHINEN (PH – AGS)
16. Emmanuel TSESMELIS (DG)
17. Rüdiger VOSS (PH – ADE

The French and Swiss Authorities will reject any request signed by a person who is not on this list.

We would like to remind you that in accordance with the memorandum of 7 December 2000 issued by the Director of the Administration, (ref. DG/DA/00-119), “the Organization shall not request any legitimisation document (or residence permit) or visa from the Host States for persons registered as EXTERNAL" (people who do not hold a contract of employment, association or apprenticeship with CERN).

We would also like to remind you that those coming to CERN should find out in good time about the conditions of entry to Switzerland and France applying to them and ensure that they obtain the requisite visas, where applicable, in the country in which they are habitually resident.

Useful information can be obtained from the Swiss and French diplomatic representations abroad, as well as from the following Web pages :

• http://www.bfm.admin.ch/content/bfm/en/home/dokumentation/rechtsgrundlagen/weisungen_und_kreisschreiben/visa/liste1_staatsangehoerigkeit.html (Swiss Federal Office for Immigration) ;

• http://www.diplomatie.gouv.fr/en/france_159/coming-to-france_2045/getting-visa_2046/general-information-for-foreign-nationals-with-ordinary-passeports_1559.html (French Ministry of Foreign and European Affairs).

The Authorities of the Host States have informed the Organization on a number of occasions that they insist upon scrupulous compliance with visa legislation.

Relations with the Host States Service
http://www.cern.ch/relations/
relations.secretariat@cern.ch

Maintenance and consolidation work has been progressing well in both the machine and the experiments in preparation for the March restart.

 

Additional work was required around Point 5 due to the discovery and repair of a problem with the RF fingers at the connection of two beam vacuum chambers in CMS. The repair has been completed successfully and the sector is now under vacuum. In order to avoid rushing the delicate final operations required for closing the detector, the restart of the machine has been postponed by one week, from 7 March to 14 March.

In the machine, the first cool-down to 1.9 K has started in several sectors ,and the cool-down of the whole machine is still planned to be finished by 21 February. The time window between 22 February and 14 March will be dedicated to powering and cryogenic tests.

Since 12 December, the Radiation Protection (RP) group has been deeply involved in the work in the accelerator complex to ensure the protection of people against ionising radiation. For this purpose, the RP group determines the hazards associated with prompt and residual radiation exposure and performs the radiological area classification, materials classification and risk analysis of work places.

“The radiation dose to carbon-based materials (cable and magnet coil insulation) used in the accelerator complex is recorded. Since last year, the LHC has been equipped with 550 radio-photoluminescent (RPL) dosimeters,” explains Julia Trummer from the Radiation Protection group. “RPL dosimeters are tiny glass cylinders of 6mm in length and 1mm in diameter. Radiation creates luminescence and colour centres in the glass. The luminescence centres are excited by a UV source and the intensity of the emitted light is related to the radiation dose. The doses that can be measured range from a few Gy up to MGy.”

“In order to prepare for future interventions – especially those during the next long shutdown – material samples are being placed in selected areas,” adds Cristina Adorisio, also an RP group member. “These samples contain materials used in the connections between the magnets. An activation measurement of these samples will help to estimate dose values to workers.”

Posted on behalf of Hannah Hoag.

Canada’s marine biodiversity is under threat and there’s no strategy for fixing it, states a report released today by the Royal Society of Canada. According to the independent panel behind the assessment, the heart of the problem lies in the conflicting responsibilities of Fisheries and Oceans Canada (DFO), a federal department with the joint role of promoting industrial and economic activity and conserving marine life and ocean health.

The international ten-person panel found that climate change, aquaculture and over-fishing were having negative effects on Canada’s marine ecosystems and species. The oceans are becoming warmer and less salty, food webs are being disrupted and disease is being transferred from farmed to wild species. The panel also gauged whether Canada was fulfilling its obligations to sustain marine biodiversity. The answer: no.

“We’ve made many commitments, but we have not met those commitments and we don’t have a plan,” says Jeff Hutchings, an expert on marine biodiversity and conservation at Dalhousie University in Halifax and the panel’s chairman.

Several national and international agreements, such as the UN Fish Stocks Agreement, commit Canada to protecting its marine biodiversity. Even so, “Canada has fallen well short of the progress made by most developed nations,” the authors write. Canada should have set targets for exploited fish stocks, including target population size and limits that aren’t to be exceeded.

“The United States, Australia, New Zealand, and increasingly parts of Europe have these plans, but we don’t have them for Canadian Atlantic cod, or for most of marine species,” says Hutchings.

Canada is also committed to establishing a national system of marine protected areas, and during a 2010 Conference of the Parties of the UN Convention on Biological Diversity, it agreed to set aside 10% of coastal and marine areas by 2020. To date, only 0.8% is protected.

The panel made seven recommendations to establish Canada as a leader in ocean stewardship and marine conservation. Among them, it urged the federal government to resolve the conflicts of interest surrounding DFO and to limit the discretionary power of the Minister of Fisheries and Oceans.

Other countries have managed to overcome such conflicts. In the United States, the Magnuson-Stevens Act requires recovery plans for over-fished stocks and provides impact assessments for fisheries. It also mandates the following of scientific advice, says Dave VanderZwaag, the Canada Research Chair in Ocean Law & Governance at Dalhousie University, and one of the panel members.

Hutchings is among those who would like to see the DFO’s fishing industry activities transferred to Industry Canada.

“If they were separated, and they probably should be, the outcome would depend on the weight the political leaders give to science and conservation. At present, the government gives little emphasis to science and even less to conservation,” says Daniel Pauly, a marine biologist at the University of British Columbia in Vancouver, who was not part of the panel.

A spokesperson for DFO would not comment on the report until it has been reviewed by the department.

It's now officially February, and the release date for How to Teach Relativity to Your Dog is only a few weeks off-- the official release date is Feb. 28. Of course, I've got a copy already:

If you would like a copy of your very own, you can either wait until the release, or take part in this shameless publicity stunt: The second-ever Dog Physics Photo Contest!

Last time around, we did a LOLEmmy contest for a bound galley proof of the first book. This time, I'm giving away a signed copy of the finished book, so we'll go for something a little trickier: I've picked three pictures from my Flickr set of dog photos, showing Emmy sitting, play-bowing, and moping. Your challenge, should you choose to accept it, is to crop her out of one of those three, and edit her into some other scene. Like this:

The best photoshopped picture of Emmy wins a signed copy of How to Teach Relativity to Your Dog. Rules and conditions below the fold:

Read the rest of this post... | Read the comments on this post...

Posted on behalf of Ichiko Fuyuno.

Nearly six years after it was proposed, Japan’s Space Activities Commission has finally approved the development of Hayabusa 2, successor to the Hayabusa asteroid probe, which returned samples to Earth in 2010 (see ‘Asteroid visit finds familiar dust’).

Hayabusa 2 will aim for 1999JU3, a small asteroid about 900 metres in diameter. The asteroid is slightly bigger than the first mission’s destination, Itokawa, but it is supposedly more primitive and contains more organic or hydrated materials, which may provide clues about the origins of the Solar System. The Japan Aerospace Exploration Agency (JAXA) plans to launch Hayabusa 2 in 2014 or 2015, land on the asteroid in 2018 and return to the Earth in 2020.

Hayabusa 2 will be closely based on its predecessor, but will incorporate many “lessons learned” from the problems encountered by the first mission. In the original Hayabusa, the ion-thrust engines died before the end of the mission, so the team will work to extend their operating life. The probe crashed down on the surface when it attempted its first landing, because of a malfunction of an obstacle-detection sensor. The sensor will be scrapped and navigation systems improved to enable a smooth touch-down.

Moreover, the original Hayabusa had expected to fire two bullets on the Itokawa surface to blast up debris that could be sampled, but it didn’t happen because of problems with the autonomous navigation systems. Instead of using bullets, the new team will develop an impactor to drop on the asteroid surface.

But aside from the technical challenges, funding could be a problem. For 2012, Hayabusa 2 has been allotted 3 billion yen (US$39 million), less than half the amount requested by JAXA and only a slice of the expected total cost of 26 billion yen ($342 million).

Image from JAXA.

Well, it has been a while since I've posted any sketches, but that does not mean that I've not been doing any. I've had a visitor and have not been on my usual routine, and so I've got a bit out of practice for not doing so many, but I still snatch the opportunity to sketch when I can. Here are a few faces and fragments of faces I grabbed on the bus and subway in recent weeks. (Click for a larger view.) I just used a ballpoint pen, and a sideways glance or few... I'm trying to decide whether [...]

By Hamish Johnston

Japan has announced that it will bid to host the International Linear Collider (ILC), which is expected to be the next big experiment in particle physics after the Large Hadron Collider at CERN. The Japanese press is saying that the particle smasher – which is expected to cost about $8bn and stretch for 40 km underground – could be built on the island of Kyushu.

The word on the street is that either Japan, CERN located on the Swiss-French border, or Fermilab in the US will play host to the massive project. Physics World's Margaret Harris was at Fermilab recently to find out what will become of the facility now that its premier collider – the Tevatron – has shut down. Margaret didn't focus on the lab's chances of bagging the ILC, but rather on the plethora of experiments that are ongoing or planned for the near future. Her article about the visit also includes a series of audio clips of Fermilab physicists describing their work.

So, do you think Fermilab is the place for the ILC? This week's poll question is:

Where should the International Linear Collider be built?

At CERN (Europe)
At Fermilab (US)
In Japan
It should never be built

Have your say by visiting our Facebook page. And feel free to explain your vote, or suggest another location, by posting a comment on the poll.

In last week's poll, we asked, "Do you believe that researchers will always view the scientific paper as the gold standard for sharing new results?". 56% of you think that the scientific paper will endure, while the remaining 44% believe the paper will be replaced by other forms of communication. That's hardly a ringing endorsement of something that has served science well for several centuries.

One thing that commenters could agree on is the importance of peer review in science communication. One voter, Robert Minchin, said "Peer review is far too useful, not just as a 'gatekeeper' for what gets into the literature, but also in preventing us from embarrassing ourselves: like most (if not all) scientists, I've had referees spot errors that I had been completely blind to." He goes on to say that while the concept of a paper will endure, they "may not be anything like we have had in the past". He added, "I would expect it to become standard for journal publishers to provide the ability to manipulate and search data tables, view them graphically, etc. as part of their value-added service."

Another pollster, Jose Riera, agrees about the importance of peer review, writing: "The real question is peer-reviewed papers or not peer-reviewed. My answer is that only peer-reviewed papers could have some minimum standards or scientific value."

Thank you for all your responses and we look forward to hearing from you again in this week's poll.

Brownian motion is a very kind mathematical object being very keen to numerical simulations. There are a plenty of them for any platform and software so that one is able to check very rapidly the proper working of a given hypothesis. For these aims, I have found very helpful the demonstration site by Wolfram and specifically this program by Andrzej Kozlowski. Andrzej gives the code to simulate Brownian motion and compute Itō integral to verify Itō lemma. This was a very good chance to check my theorems recently given here by some numerical work. So, I have written a simple code on Matlab that I give here (rename from .doc to .m to use with Matlab).

Here is a sample of output:

As you could note, the agreement is almost perfect. I have had to rescale with a multiplicative factor as the square root appears somewhat magnified after the square but the pattern is there. You can do checks by yourselves. So, all my equations are perfectly defined as is a possible square root of a Wiener process.

Of course, improvements, advices or criticisms are very welcome.

Marco Frasca (2012). Quantum mechanics is the square root of a stochastic process arXiv arXiv: 1201.5091v2

Filed under: Mathematical Physics, mathematics, Physics, Quantum mechanics Tagged: Brownian motion, Itō calculus, Itō integral, Stochastic processes

Today the CMS collaboration revealed several new analyses based on the full dataset the LHC collected in 2011. As usually, the recurrent theme was "no-significant-excess-was-found". Here is a selection of the most interesting searches and limits.

t' searches
In this analysis, filed under "4th generation", one looks for a heavier copy of the top quark: a fermionic particle with charge 2/3 produced in pairs and decaying to one b-quark and one W boson. We sort of know by now there is no 4th generation of quarks and leptons in nature, nevertheless this search is relevant to more interesting new physics models. For example, in a large class of little Higgs and composite Higgs models the fermionic partner of the top quark decays as t' → b W about half of the time. The current limit on the t' mass assuming 100% branching fraction for the t' → b W decay is 525 GeV. For little Higgs et al. the limit is slightly weaker, slightly above 400 GeV (due to the smaller branching fraction) but that is also beginning to feel uncomfortable from the point of view of naturalness of these models.

W' searches
This time the target is a heavy cousin of the W boson, decaying to one lepton and one neutrino. Unlike in the former case, there is no compelling theoretical reasons for such a creature to exist. However they represent a characteristic and clean signature that is fairly straightforward to look for: an energetic electron or muon accompanied by missing energy from a neutrino. To tell W' from the ordinary W boson one looks for events with a large transverse mass (for an on-shell particle whose decay products include a neutrino the transverse mass is less than the particle mass). Intriguingly, in the muon channel an outlier event with a very large transverse mass of 2.4 TeV is observed in the data. Of course, most likely it's just a fluke, but in any case it'll be interesting to see what ATLAS has in store.

t-tbar resonance searches
This search targets heavy (more than 1 TeV) particles decaying to a pair of top quarks, a signature very common in models with a new strongly interacting sector, like composite Higgs or the Randall-Sundrum model. Such a particle would produce a bump in the invariant mass spectrum of t-tbar pairs, which are otherwise copiously produced at the LHC. Top quark decays most often to 3 hadronic jets, but for a heavy mother resonance the daughter top quarks move so quickly that their decay products merge into one fat jet. Therefore this search relies on fancy modern techniques of studying substructure of jets, in order to identify closely packed jets that could originate from a fast moving top quark. No resonance is observed in the t-tbar spectrum. What is interesting is that the LHC sensitivity now reaches the cross sections predicted by popular versions of the Randall-Sundrum model, excluding Kaluza-Klein gluons lighter than about 1.5 TeV. My guess is that the explanation of the Tevatron anomalous top forward-backward asymmetry in terms of heavy KK gluon is now dead and gone.

SUSY searches
The only vanilla SUSY search updated with the full 2011 dataset is the one in the Z+jets+missing energy channel. This is not the first place you'd look for supersymmetry (that would be jets+MET); this search is relevant to a subset of models where a cascade of neutralinos and gravitons produces, often enough, an shell Z boson. Therefore the limits on the gluino mass are not stunning: 600-900 GeV depending on how squeezed is the SUSY spectrum. More spectacular SUSY limits are probably saved for the Moriond conference in about 1 month from now.


For more details, more models, more limits, and more disappointment have a look at the slides or the original summary notes on the CMS wiki page.

At the beginning of 2012, particle physicists are in such a confusing state of mind: Higgs has been practically discovered but we're not allowed to celebrate yet. It's like when your football team is on top of the league, playing in the last round against a relegated team and winning 2:0 after the first half; nothing is decided yet, anything may happen, but... come on... So, to stay sane, most of us act as if the 125 GeV Higgs were a fact and work out the consequences.

In that vein, this post is about a complicated relationship between the 125 GeV Higgs and supersymmetry. There is this lore that SUSY predicts the Higgs mass below 130 GeV, and you might have heard people saying that the recent almost-discovery of the Higgs is an incredible success of supersymmetry. Well, strictly speaking, the number 130 GeV is taken out of my ass. Instead, with some degree of rigor, one can make the following 3 statements:

1. Minimal SUSY without fine-tuning predicts the Higgs mass close to the Z boson mass, that is about 90 GeV.
2. Minimal SUSY ignoring fine-tuning predicts the Higgs boson lighter than 160 GeV.
3. Non-minimal SUSY in general makes no predictions about the Higgs mass.
   

The last point is pretty obvious: once you agree to extend the minimal supersymmetric model (MSSM) then options become infinite. Even straightforward extensions of the MSSM, such as the NMSSM with one additional singlet field in the Higgs sector, allow one to cover the entire Higgs mass range up to almost a TeV. (You might be confused if you heard that the NMSSM predicts the Higgs mass below 140 GeV. That however is the case when the Higgs self-coupling is required to stay perturbative all the way up to the GUT scale, a strong and not particularly motivated assumption.)

The statement #1 on my list boils down to the fact that in the MSSM the quartic term in the Higgs potential (which fixes the Higgs mass, given its vacuum expectation value) is not a free parameter. Instead, supersymmetry ties the quartic coupling to the electroweak gauge couplings.
Up to 1-loop precision the Higgs mass is given by the formula:
(for vanishing A-terms, a large tanβ, and universal stop masses, and setting yt=1). In the first approximation one gets the famous bound m_Higgs ≤ m_Z. Thus, if the MSSM were for real, the Higgs should have been seen at LEP.

Only when supersymmetry is badly broken, that is when the top mass is much smaller than the mass of its scalar partner the stop, the one-loop logarithmic term can be large enough to raise the Higgs mass considerably above the Z boson mass. In particular, for the 125 GeV Higgs the tree-level and loop contributions must be, amusingly, almost exactly equal. The price for making the stop mass large goes under the name of fine-tuning. Since vacuum equations in the MSSM generically marry the SUSY scale to the weak scale, m_stop ~ m_Z , as soon m_stop >> m_top one needs to carefully tune the parameters of the theory so as to cancel various excessive contributions to the Z boson mass. This goes against the original motivation for supersymmetry which was precisely to exorcise fine-tuning.

This brings us the statement #2 on my list. When the fine-tuning issue is ignored, the scenario known as split supersymmetry (SS), the Higgs mass in the MSSM can be much larger than the Z boson mass. In the plot on the right (from this paper), you can see that the Higgs mass can reach 155 GeV for scalar SUSY partner masses at the GUT scale. From the same plot, one finds that the 125 GeV mass correspond to roughly 10 TeV squark masses. Thus, the almost-discovery of the 125 GeV Higgs at the LHC clearly points to Somewhat Split Supersymmetry (SSS) ;-)

All in all, the story of Higgs and SUSY is getting less like a Hollywood romance and more like a Ken Loach movie of hardship and misery. Of course, it is well known that 10 TeV squark masses are not an inevitable consequence of the MSSM and 125 GeV Higgs. Playing with another SUSY breaking parameter, the so-called A-term, the Higgs mass can be dialed to any desired value. When the A-term is judiciously chosen, the scalar top partners could even be at a few hundred GeV, well within the reach of last year's LHC run. See the violet band in the plot on the right. Thus a happy ending cannot be completely excluded at this point. However, more and more theorists are beginning to prepare an exit strategy, like ...nobody said SUSY had to show up at the LHC, maybe fine-tuning 1:1000 is not so bad, maybe SUSY is really at 10 TeV, etc... In a sense, this is right: from the theory point of view there is no fundamental difference between 1 in 100 and 1 in 1000 fine-tuning. Only a practical one, for LHC experimentalists :-)

To wrap up this inflammatory post: the point I was trying to make is that 125 GeV Higgs is not a successful prediction but rather a serious setback from the point of view of SUSY. In non-minimal SUSY any Higgs mass is possible. Minimal SUSY can accommodate any mass up to almost 160 GeV, depending on how much fine-tuning you're willing to accept; 125 GeV Higgs points to 10 TeV squarks, outside the LHC reach.

As I keep saying in various posts, I'm teaching a class on timekeeping this term, which has included discussion of really primitive timekeeping devices like sundials, as well as a discussion of the importance of timekeeping for navigation. To give students an idea of how this works, I arranged an experimental demonstration, coordinated with Rhett at Dot Physics. We've been trying to do this literally for months, but the weather wouldn't cooperate. Until this past weekend, when we finally managed to make measurements that allow us to do some cutting-edge science. For 200 BC, anyway...

So, what did we do? Well, we each made a sundial, and shot time-lapse video of it using a webcam. Here's mine-- note the Lego gnomon, graciously donated to science by SteelyKid (whose attempts to help with "Daddy's 'spermint" weren't enough to earn a co-author credit, but do rate this acknowledgement):

The too-bright first few frames are because I forgot to adjust the exposure initially, and the greying out at the end is because some thick clouds rolled in. This was shot in our back yard in Niskayuna, and simultaneously (in some frame of reference, anyway), Rhett was taking video of his own sundial, in Hammond, LA. I took both videos, and ran them through Tracker video to measure the position of the end of the shadow for each frame, and produced the following results:

Read the rest of this post... | Read the comments on this post...

Editor’s note: This article comes from US LHC intern Amy Dusto, who is currently working as a communicator at CERN. She is introducing LHC Lunch, a series of articles and videos she created while getting to know some of the members of experiments at the Large Hadron Collider from U.S. institutions. The busy cafeteria known [...]

I think that this is a sad reflection of the times we live in, especially when people can send out things anonymously and threaten others for doing their jobs.

This article looks at the challenges being faced by climate scientists, and not on the task they faced with their jobs either!

Harassment of climate scientists by climate-change deniers goes back at least to 1995, after the IPCC published its Second Assessment Report. Santer was the lead author of chapter 8, which looked at the causes of climate change. “The single sentence ‘The balance of evidence suggests a discernible human influence on global climate’ changed my life,” he says. “I was the guy who was associated with this sentence. Those who did not like that finding did everything not only to undermine the finding but also to undermine my scientific reputation.”

 

The harassment has ramped up in recent years, says Michael Mann of the Pennsylvania State University, whose book The Hockey Stick and the Climate Wars: Dispatches from the Front Lines, due to be published by Columbia University Press in early March, includes a retelling of his own ongoing experiences with harassment. “Political intimidation, character attacks, what appear to be orchestrated phone and email campaigns, nasty and thinly veiled threats, not just to us but to our families, are what it means in modern American life to be a climate scientist,” says Mann. Even this magazine, after publishing last October articles on the science of climate change—about its being under fire and about communicating that science to the public—received an abundance of letters with the tenor, “How could PHYSICS TODAY print such a one-sided portrayal of climate science when many reputable scientists disagree?”

 

Fossil-fuel interests, says Gavin Schmidt, a climate researcher at NASA, “have adopted a shoot-the-messenger approach. It’s been a very successful strategy. They have created a chilling effect, so other [scientists] won’t say what they think and the conversation in public stays bereft of anyone who knows what they are talking about.” Schmidt cofounded RealClimate.org, a forum for climate scientists to “provide a quick response to developing stories and provide the context sometimes missing in mainstream commentary.” Meanwhile, the Competitive Enterprise Institute, a vocal opponent to limiting greenhouse gas emissions, is suing NASA for the release of Schmidt’s personal emails.

This, of course, is made worse when politicians, people who should know better but don't, somehow voice the same level of skepticism. In the minds of some feeble-minded climate deniers, this gives them legitimacy to go after these scientists.

This may be the 21st Century. But some aspect of the Dark Ages still persists, and prosecution of scientists appears to be one of them.

Zz.

I'll highlight the link to this important article in Physics Today, but I haven't had time to read it carefully yet. I've only skimmed through some of the highlighted points and figures, but I'm not going to comment on this till I read it properly. Unfortunately, I've been horrendously busy with work lately. But it shouldn't stop you from having a go at it.

Zz.

It goes under the name spacetime-foam or fuzz, or sometimes graininess or, more neutral, fluctuations: The general expectation that, due to quantum gravitational effects, spacetime on very short distance scales is not nice and smooth but, well, fuzzy or grainy or foamy.

If that seems somewhat fuzzy to you, it's because it is. Absent an experimentally verified and generally accepted theory of quantum gravity, nobody really knows what exactly spacetime foam looks like. A case for the phenomenlogists then! And, indeed, over the decades several models have been suggested to describe spacetime's foamy, fuzzy grains, based on a few simple assumptions. The idea is not that these models are fundamentally the correct description of spacetime but that they can, ideally, be tested against data, so that we can learn something about the general properties that we should expect the fundamental theory to deliver.

One example for such a model, going back to Amelino-Camelia in 1999, is that spacetime foam causes a particle to make a random walk in the direction of propagation. For each step of distance of the Planck length, l_P, the particle randomly gains or loses another step. This is a useful model because random walks in one dimension are very well understood. Over a total distance L that consists of N =L/l_P steps, the average deviation from the mean is the length of the step times the square root of the number of steps. Thus, over a distance L, a particle deviates a distance

where I have put in a dimensionless constant α - for a quantum gravitational effect, we would expect it to be of order one. See also the below figure for illustration and keep in mind that c=1 on this blog

While simple, this model is not, and probably was never meant to be, particularly compelling. Leaving aside that it's not Lorentz-invariant, there is no good reason why the steps should be discrete or be aligned in one direction. One might have hoped that this general idea would be worked out to become somewhat more plausible. Yet that never happened because this model was ruled out pretty much as soon as it was proposed. The reason is that if you consider the detection of lightrays from some source, the deviation from the normal propagation on the light-cone will have the effect of allowing different phases of the emitted light to arrive at once. The average phase blur is

If the phase blur is comparable to 2π, interferences would be washed out. See below figure for illustration

As it happens however, interference patterns, known as Airy rings, can be observed on objects as far as some Gpc away from earth. If you put in the numbers, for such a large distance and α ≈ 1 the phase should be entirely smeared out. To the right you see an actual image of such a distant quasar from the Hubble Space Telescope (Figure 3 from astro-ph/0610422). You can clearly see the interference rings. And there goes the random walk model.

There is a similar model going back to Wheeler and later Ng and Van Dam, that the authors have called the "holographic foam" model. (Probably because everything holographic was chic in the late 1990s. Except for the general scaling it has little to do with holography.) In any case, the main feature of this model is that the deviation from the mean goes with the 3rd root, rather than the square root, of N. Thus, the effects are smaller.

It is amazing though how quickly smart people can find ways to punch holes in your models. Already in 2003 it was pointed out, that with some classical optic formulas from the late 19th century, modern telescopes allow to set much tighter bounds. Roughly speaking, the reason is that a telescope with diameter D focuses a much larger part of the light's wavefront than just one wavelength λ. The telescope is very sensitive to phase-smearing all over its opening. Telescopes are for example sensitive to air turbulences, a problem that the Hubble Space Telescope does not have.

The sensitivity of a telescope to such phase distortions can be quantified by a pure number known as the "Strehl ratio." The closer the Strehl ratio is to 1, the closer the telescope's images are to those of an ideal telescope, showing a point-like sources as a perfect Airy patterns. A non-ideal telescope will cause an image degradation, most importantly a smearing of the intensity. The same effect would be caused by the holographic space-time fuzz. Thus, up to the telescope's limit on image quality, the additional phase distortion would be observable: it lowers the Strehl ratio of images of very far-away objects such as quasars. (Though, if it was observed, one wouldn't know exactly what its origin is.)

The relevant point is that, using the telescope's sensitivity to image degradation, one gains an additional factor of D/λ ≈ 10⁸. In their paper:

No quantum gravity signature from the farthest quasars
By Fabrizio Tamburini, Carmine Cuofano, Massimo Della Valle, Roberto Gilmozzi

the authors have presented an analysis of the images of 157 high-redshift (z > 4) quasi-stellar objects. They found no blurring. With that, also the holographic foam model is ruled out. Or, to be precise, the parameter α is constrained into a range that is implausible for quantum gravitational effects.

As it is often the case in the phenomenology of quantum gravity, the plausible models are difficult, if not impossible, to constrain by data. And the implausible ones nobody misses when they are ruled out. This is a case of the latter.

Thanks to Neil for reminding me of that paper.

---

PS: We were not able to find a derivation for the exact expression for the phase blurring as a function of the Strehl ratio, Eq. (5), that is used in the paper. We got so far that it's called the Marechal approximation. If you know of a useful reference, we'd be interested!

Yesterday I spent the afternoon at the Third Indian-Israeli International Meeting on String Theory,  held at the Israel Institute for Advanced Studies.  The subject of the meeting is “Holography and its Applications”.  No, this isn’t holography as in that optical trick that allows you to create a three-dimensional image on the security strip of your credit card — this is “holography” as string theorists like to discuss it, that trick of describing gravitational or string-theoretic physics  in a certain number of spatial dimensions as quantum field theory (without gravity) in a smaller number of spatial dimensions.  It’s impressive, even stunning, that sometimes you can use a precise form of the holographic principle to solve some difficult string theory problems by rewriting them as easier quantum field theory problems, and solve some difficult quantum field theory problems by rewriting them as easier string theory problems.

I worked in this research area on and off for quite a while (mainly 1999-2007) so I know most of the participants in this subfield.  In fact my most commonly cited paper happens to be on this subject.  But ironically my role at this conference was to present, as the opening talk, a review of 2011 at the Large Hadron Collider (LHC).

My talk started with an extended introduction, a sort of “everything you absolutely have to know if you want to understand what’s happening at the LHC.”  Most string theorists know a lot of particle physics, and most are aware of what is happening at the LHC, but most of them don’t know all the details.  [Well, after yesterday, some of them know a lot more details than before, maybe more than they wanted.]   Then I talked about some of the most basic things we learned in 2011 from the LHC:

• quantum field theory (the mathematics used in particle physics) in general, and specifically quantum chromodynamics (the mathematics used to predict the behavior of quarks and gluons), still work just fine, as far up in energy as the LHC’s data can currently reach, roughly 3 TeV or so (see Figure 1);
• if there are new phenomena occurring at the LHC, they most likely are not produced with very large rates, or they involve particles that decay in a complex fashion, one that does not easily stand out in the most common searches;
• the most popular forms of supersymmetry and some other similar theories (which have high production rates and would generally stand out) are increasingly disfavored, though other more tricky variants still remain largely unconstrained;
• partner particles for the top quark, widely expected in many models that attempt to address the hierarchy problem, haven’t been observed (see Figure 2), though the searches are hard and haven’t gotten that far yet.  There’s a lot more work to do over the coming years — especially in the case of supersymmetric partners (top squarks, as they are called) which are particularly tough;
• and a few other things…

I entitled my talk “Juggernaut and Behemoth”, two words that seem appropriate in describing the LHC, and that have entered the English language (mispronounced, of course) from the long and great traditions of the two cultures most closely associated with the conference, the Hindu and the Hebrew.  Juggernaut, which in English conveys a notion of something powerful and unstoppable, is a rough translation of Jaggannath, a Hindi word meaning “Lord of the Universe” and referring to the god Vishnu.  Behemoth, which in English implies a huge creature, is a monster described in the book of Job (from the Old Testament, i.e. Jewish, portion of the Bible). In bringing these images to mind, I intended to suggest not only the physical size and scale of the LHC but also the  daunting amount of data, of information, and of knowledge that it generates, and the immense importance of its scientific research program, both in informing our understanding of the basic workings of our universe and in determining the future of particle physics as an intellectual endeavor.  In many respects, the LHC borders on overwhelming.

Unfortunately I couldn’t go back to the meeting today, because this morning I had the honor to give the weekly colloquium at the Weizmann Institute, my hosts during this short visit.  When I first wrote a colloquium talk on the LHC, back in 2007, I could give it several times in a row before it would go out of date. But nowadays, things change so quickly that I have to update the colloquium for each presentation… especially the section on the Higgs particle!

Expectations are that we will get a little more news on the Higgs searches pretty soon — within a week or so.

Filed under: LHC News, Particle Physics Tagged: atlas, cms, ExtraDimensions, Higgs, particle physics, searches, supersymmetry

I just received this announcement for the opening of a (tenured/civil servant) position in the national research institute in biostatistics, genetics, and agronomy, INRA:

Position opening with profile Approximate inference techniques in complex systems

Key activities and required skills: You will develop methodological research in the field of statistical inference for models used in environmental sciences. These inference techniques will account for the complex dependency structure due to the temporal, spatial and evolutionary organisation of the observations, for the heterogeneity of the data and for the existence of unobserved variables or incomplete data. Solid experience in statistical modelling of complex data (graphic models, multi-scale spatio-temporal data) and a strong orientation towards the applications in environment and biology would be appreciated. Skills in approximation techniques (variational inference, ABC techniques) will be welcome.

Contact person: Stéphane Robin (robin [chez] agroparistech [lepoint] fr)

Location:  Versailles-Grignon (Paris)

Deadline: February 25, 2012

Website: INRA offer

This should appeal to (some) readers of the blog, esp. since the offer has no nationality constraint.

Filed under: R, Statistics, Travel, University life Tagged: ABC, INRA, job offer, Paris-Grignon, variational Bayes methods, Versailles

Just how ants create the highly efficient network of trails around their nests has never been fully understood. Now researchers think they've cracked it

Among the most impressive transportation networks on the planet are the complex trails that ants create around their nests. These networks arise through the ants' exploration of their environment and end up channelling the distribution of food for the colony and the daily movements hundreds of thousands of individuals.

What's more, these networks aren't just a random criss-crossing of space. Instead, they are a highly efficient solutions to the problem of searching and transporting food. Various groups have created ant-like foraging algorithms to do other types of virtual exploration.  

One question that has fascinated biologists is how ants build these networks. They've known for some time that ants leave small deposits of pheromones as they travel and that other ants follow these trails, leaving their own deposits. This increases the concentration of the pheromone, strengthening the trail. 

But the precise algorithm that governs the way ants respond to pheromones has been harder to pin down. Many experiments show that a trail can only be reinforced if ants have a disproportionately higher probability to follow a  trail with higher pheromone concentration.  

Biologists have always assumed that this disproportionate response means ants must have a non-linear response to the chemical. In other words, an ant's tendency to turn towards a pheromone deposit is related in a non-linear fashion to the concentration.

But that seems to conflict with one of the great triumphs of experimental biology--Weber's Law, which relates the perceived intensity of a stimulus to its physical magnitude. Biologists know this holds for the human perception of many stimuli, such as the intensity of sound, and have also verified it in many insects. So why not in ants?

Today, Andrea Perna at the Complex Systems Institute of Paris Ile de France and a few pals, resolve the issue. These guys have developed an entirely new way to image pheromone trails which allows them to study ant response to pheromones in more detail than ever before. 

They say the structure of ant trails can be entirely explained if the ants's response to a pheromone droplet concentration is linear. "One ant will turn to the left in proportion to the difference between the pheromone it has on its left side and the pheromone on its right," say Perna and co.

They also point out that this is exactly what Weber's law predicts.

So where does the non-linearity required to create trails come from? Perna and co say that ant behaviour is inevitably noisy.  "We show that the required non-linearity does not reside in the perceptual response of the ants, but in the noise associated with their movement," they say.

That's a fascinating result because it reveals how complexity in nature forms with the simplest of inputs. 

And it clearly has implications for the study of other complex structures that ants create, such as their nests. Just how ants create these huge vibrant structures has long puzzled biologists. 

Perna and friends hint at an answer in their conclusion. "We can imagine that other collective phenomena, such as group decision-making, could also be founded on coupling between Weber’s Law and simple feedback mechanisms."

In the case of nests, this mechanism would have to operate in three dimensions rather than two. But that shouldn't be too much of a challenge. Perhaps a problem that a relatively simple computer model could help solve.    

Ref: arxiv.org/abs/1201.5827 :Individual Rules For Trail Pattern Formation In Argentine Ants (Linepithema Humile)

As you may know, there’s a wonderful and famous analogy between classical mechanics and electrical circuit theory. I explained it back in “week288″, so I won’t repeat that story now. If you don’t know what I’m talking about, take a look!

This analogy opens up the possibility of quantizing electrical circuits by straightforwardly copying the way we quantize classical mechanics problems. I’d often wondered if this would be useful.

It is, and people have done it:

• Michel H. Devoret, Quantum fluctuations in electrical circuits.

Michel Devoret, Rob Schoelkopf and others call this idea quantronics: the study of mesoscopic electronic effects in which collective degrees of freedom like currents and voltages behave quantum mechanically.

I just learned about this from a talk by Sean Barrett here in Coogee. There are lots of cool applications, but right now I’m mainly interested in how this extends the set of analogies between different physical theories.

One interesting thing is how they quantize circuits with resistors. Over in classical mechanics, this corresponds to systems with friction. These systems, called ‘dissipative’ systems, don’t have a conserved energy. More precisely, energy leaks out of the system under consideration and gets transferred to the environment in the form of heat. It’s hard to quantize systems where energy isn’t conserved, so people in quantronics model resistors as infinite chains of inductors and capacitors: see the ‘LC ladder circuit’ on page 15 of Devoret’s notes. This idea is also the basis of the Caldeira–Leggett model of a particle coupled to a heat bath made of harmonic oscillators: it amounts to including the environment as part of the system being studied.

I received this email a few days ago:

I am an hard-core reader of your blog and thanks to your posts I have recently started being interested to ABC (and Bayesian methods in general). I am writing you to ask for suggestions on the application of the semi-automatic ABC à la Fearnhead & Prangle. The reason why I am contacting you instead of addressing the authors is because (i) you have been involved in the RSS reading of their paper and (ii) you are an authority on ABC, and therefore you are probably best suited and less biased on such issue. I am applying ABC with the semi-automatic statistics selection provided in Fearnhead and Prangle (2012) to a problem which can be formalized as a hidden Markov model. However I am unsure of whether I am making a huge mistake on the following point: let’s suppose we have an unobserved (latent) system state X (depending on an unknown parameter θ) and a corresponding “corrupted” version which is observed with some measurement error, e.g.

Y = X + ε,

where ε is the measurement error independent of X, ε is N(0, σ²), say. Now their setup does not consider measurement error, so I wonder if the following is correct. Since I can simulate n times some X’ from p(X|θ) am I allowed to use the corresponding “simulated” n corrupted measurements

Y’ = X’ + ε’

(where ε’ is a draw from p(ε|σ)) into their regression approach to determine a (vector of) summary statistic S=(S1,S2) for (θ,σ)? I mean the Y’ are draws from a p(y|X’,θ,σ) which is conditional on X’. Is this allowed? Wilkinson (2008) is the only reference I have found considering ABC with measurement-error (the ones by Dean et al (2011) and Jasra et al (2011) being too technical in my opinion to allow a practical implementation) and since he does not consider a summary statistics-based approach (e.g. Algorithm D, page 10) of course he is not in need to simulate the corrupted measurements but only the latent ones. Therefore I am a bit unsure on whether it is statistically ok to simulate Y’ conditionally on X’ or if there is some theoretical issue that makes this nonsense.

to which I replied

…about your model and question, there is no theoretical difficulty in simulating x’ then y’given x’ and a value of the parameters. The reason is that

.the proper marginal as defined by the model. Using the intermediate x’ is a way to bypass the integral but this is 100% correct!…

a reply followed by a further request for precision

Although your equation is clearly true, I am not sure I fully grasp the issue, so I am asking for confirmation. Yes, as you noticed I need a

y’ ~ f(y’|θ,σ)

Now it’s certainly true that I can generate a draw x’ from f(x’|θ,σ) and then plug such x’ into f(y’|x’,θ,σ) to generate y’. By proceeding this way I obtain a draw (y’,x’) from f(y’,x’|θ,σ). I think I understood your reasoning, on how by using the procedure above I am actually skipping the computation of the integral in:

Is it basically the case that the mechanism above is just a classic simulation from a bivariate distribution, where since I am interested in the marginal f(y’|θ,σ) I simulate from the joint density f(y’,x’|θ,σ) and then discard the x’ output?

which is indeed a correct interpretation. When simulating from a joint, the marginals are by-products of the simulation.

Filed under: Statistics, University life Tagged: ANC, HMM, joint distribution, marginal, mixture, semi-automatic ABC, summary statistics

I started teaching Nuclear and Particle Physics to the 3rd year Physics students today. I decided to warm up with a few basics about elementary particles and their properties – all pretty standard stuff and no hairy mathematics. Cue pretty picture:

This doesn’t show the whole picture, of course, because for every particle there is an antiparticle, so there are antiquarks and antileptons. The existence of these was first suggested by Paul Dirac in 1928 based on his investigations into relativistic quantum theory, basically because invariance of special relativity is compatible with the existence of both positive and negative energy states, i.e.

has two sets of solutions, one with and the other with . Instead of simply assuming the latter set were physically unrealistic, Dirac postulated that they might be real, but completely filled in “empty” space; these filled negative-energy states are usually called the “Dirac Sea”. Injection of an appropriate amount of energy can promote something from a negative state into a positive one, leaving behind a kind of hole (very similar to what  happens in the case of semiconductor). This process creates a pair consisting of a (positive energy) particle and a (negative energy) antiparticle (i.e. a hole in the Dirac Sea). In the case of electrons, the hole is called a positron.

The alternative, and even wackier, explanation of antimatter I usually mention in these lectures derives, I think, from Feynam who noted that in quantum (wave) mechanics the time evolution of particles involves things like

which have the property that changing into has the same effect as changing into . This is, in essence, the reason why, in Feynman diagrams, antiparticles are usually represented as particles travelling backwards in time…

This is a useful convention from the point-of-view of using such diagrams in calculations, but it allows one also to raise the wacky bar to a higher level still, to a suggestion that, coincidentally, was  doing the rounds very recently – namely whether it is possible that there may really be only one electron in the entire Universe:

….I received a telephone call one day at the graduate college at Princeton from Professor Wheeler, in which he said, “Feynman, I know why all electrons have the same charge and the same mass” “Why?” “Because, they are all the same electron!” And, then he explained on the telephone, “suppose that the world lines which we were ordinarily considering before in time and space—instead of only going up in time were a tremendous knot, and then, when we cut through the knot, by the plane corresponding to a fixed time, we would see many, many world lines and that would represent many electrons, except for one thing. If in one section this is an ordinary electron world line, in the section in which it reversed itself and is coming back from the future we have the wrong sign to the proper time—to the proper four velocities—and that’s equivalent to changing the sign of the charge, and, therefore, that part of a path would act like a positron.”

—Feynman, Richard, Nobel Lecture December 11, 1965

In other words, a single electron can appear in many different places simultaneously if it is allowed to travel backwards and forwards in time…

I think this is a brilliant idea, especially if you like science fiction stories, but there’s a tiny problem with it in terms of science fact. In order for it to work there should be as many positrons in the Universe as there are electrons. Where are they?

Follow @telescoper

In 2015, NASA’s New Horizons spacecraft will zip past Pluto, giving us our first close-up view of this tiny world.

The team behind the space probe have a nice idea to help raise awareness of it: make a new US Post Office stamp commemorating it. My friend Dan Durda, both an accomplished astronomer and artist, created this lovely design of the stamp:

[Click to enhadesenate. Note: the word "Forever" means the stamp is always good for first class postage, and is crossed out here to prevent forgery.]

It shows the spacecraft going by Pluto and its (relatively) freakishly large moon Charon. I like how he didn’t go for photorealism, but instead used an oil paint-like feel for it. The stamp is meant as a followup — I might even say send-up — of a US stamp issued in 1990 about Pluto that has the label "Not Yet Explored".

I like this stamp! I’d love to see it made official, too. Alan Stern, the head guy for the mission, created a petition to help that along. It takes more than just a nice stamp design to get the PO’s notice; it has to have public support as well. I signed the petition, and if you want to, please do.

I’ll note that I expect this to raise the specter of whether Pluto is a planet or not. I have some thoughts on that, and I’ll be posting again soon on that topic.

---

Related posts:

- Pluto has another moon!
- Find cold, distant worlds with Ice Hunters
- Pluto still may be the biggest dwarf planet
- Percy, Percy, me

Since 2000, the three Sloan Digital Sky Surveys (SDSS I, II, and III) have surveyed well over a quarter of the night sky, producing the biggest 3-D color map of the Universe ever made. Now, scientists have used this visual information for the most accurate computation yet of how matter clumped together – from a time when the universe was only half its present age until now.

It's apparently a good day for asking questions of the readership, so here's another one: as SteelyKid has gotten older and more active, she's become a real drain on productivity, especially at bedtime. Bedtime is now a process rather like a certain spoof book, extending well over an hour, and involving repeated requests to come back into her room for some silly reason or another. If I don't respond quickly enough, she'll work herself up into a real tantrum, so I pretty much need to stay upstairs in our bedroom until she's asleep. Which means either I can't get any work done, or I have to try to do work on my laptop in bed, which is wrecking my neck.

Thus, I'm looking to get some sort of lap desk type thing that would allow me to work on the computer in bed without doing myself harm. There are a nearly infinite variety if lap desks for sale out there, but it's sort of hard to distinguish between them based only on web sites. Thus, if anybody has relevant experience and would like to recommend a solution for this, well, you know where the comments are.

Read the comments on this post...

By Matin Durrani

The February issue of Physics World magazine is now out, featuring some great articles that I think I ought to tell you about.

Physics comes to life – Mark Haw from the University of Strathclyde and Otti Croze from the University of Glasgow explore the strange world of swimming micro-organisms – and how it is having an impact on biology, biotechnology and fundamental physics.

Gallery of whispers – Oliver Wright from Hokkaido University in Japan looks at a little-known effect dubbed "whispering-gallery waves". Dating back to the work of Lord Rayleigh at St Paul's Cathedral in London, it appears throughout science in fields as diverse as astronomy, optics and acoustics.

Securing the future – John Womersley, chief executive of the UK's Science and Technology Facilities Council, explains why the country's research community needs to safeguard its own future.

Careers, interrupted – Jan West describes the work of the Daphne Jackson Trust, which has helped more than 200 people to return to working in science after a career break.

Don't miss either Rick Trebino's Lateral Thoughts article "Fire in a crowded theatre", while over in news and analysis, we have an interview with Italian theorist Giorgio Parisi entitled "The Italian activist" and an update on the work of the SESAME synchrotron being built in the Middle East. Plus enjoy Margaret Harris's feature "Fermilab's next frontier" in all its glory.

Members of the Institute of Physics (IOP) can read the new issue free online through the digital version of the magazine by following this link or by downloading the Physics World app to your iPhone or iPad or Android device, available from the App Store and Android Marketplace, respectively.

If you're not yet a member, you can join the IOP as an imember for just £15, €20 or $25 a year via this link. Being an imember gives you a year's access to Physics World both online and through the apps.

It’s a cold and gloomy morning as befitting the first of February, so I thought you might appreciate a touch of the warmth of the South of France. This is Germont’s Aria Di Provenza il mar, il suol from La Traviata by Giuseppi Verdi. The recording – made, incredibly, in 1907 – provides a rare chance to hear the magnificent baritone of the legendary Titta Ruffo whose nickname, appropriately enough, was Voce del Lione “Voice of the Lion”. Despite the limitations of the recording, which required the aria to be cut down to fit within 3 minutes, this is still a stunning performance which makes most modern-day baritones sound like a wet weekend. If you listen carefully right at the end you’ll hear someone say “bravo”…

Follow @telescoper

Geophysicists want to use neutrinos to 'x-ray' the Earth, a technique that could reveal undiscovered oil fields. But how practical is such a scheme?

Neutrinos are peculiar particles. They have little mass, no charge and come in three flavours. These flavours are not fixed. The strange thing about neutrinos is that once created, they change from one flavour to another as they travel. 

For a long time, that puzzled physicists. A neutrino's variety determines how it interacts with matter. Physicists built experiments to detect  the flavour coming out of the Sun only to find far fewer than they expected. 

In 2001, that mystery was solved when they discovered that the missing neutrinos had flipped, or oscillated from one flavour to another, during their journey from the Sun to the Earth.  

Since then physicists have scrambled to understand neutrino oscillations in more detail. It turns out that the effect is sensitive to the distance that the neutrinos have travelled and also to the amount of matter the particles have passed through.  

That's given Carlos Arguelles and pals at the Pontifical Catholic University of Peru in Lima an idea. These guys say that  neutrino oscillations ought to be sensitive to changes in the density of the Earth. 

So the oscillations in a beam of neutrinos created at one point on the Earth and beamed through the crust to another point, ought to reveal information about any change in density along the way.  

These guys aren't the first to suggest that a neutrinos beam can effectively x-ray the Earth. But they are the first to explore the size and shape of the density changes that ought to be visible using this method. 

They say the technique ought to be able to spot cavities some 200 km across or larger filled with water,  iron-based minerals or even regions of charge accumulations. They suggest that this might take as little as 3 months.

That's interesting because some seismologists suggest that earthquakes lead to the accumulation of charge in specific volumes of rock, so the technique might be useful for studying this. 

But there's a more significant factor driving interest in this work. This technique could also reveal geological formations likely to contain oil and so could attract considerable commercial investment.   

One important question, however, is whether Arguelles and co have made realistic assumptions in their model. One problem they face is that the beam of neutrinos must be intense enough to produce a result in a reasonable period of time--certainly less than 18 months. 

To achieve this, Arguelle and co have to assume that it is possible to create beams at a rate some 5000 times higher than is achievable today.

Since it's not at all clear how this could be done, that's a big fly in the ointment. 

So while this technique looks possible in theory, this kind of assumption places a big question mark over whether it will be possible in practice in the foreseeable future.

Ref: arxiv.org/abs/1201.6080 : Searching For Cavities Of Various Densities In The Earth’s Crust With A Low-Energy ν¯e β-Beam

 

In 2009, Erik Verlinde argued that gravity is an entropic force. This created a big stir—and it helped him win about $6,500,000 in prize money and grants! But what the heck is an ‘entropic force’, anyway?

Entropic forces are nothing unusual: you’ve felt one if you’ve ever stretched a rubber band. Why does a rubber band pull back when you stretch it? You might think it’s because a stretched rubber band has more energy than an unstretched one. That would indeed be a fine explanation for a metal spring. But rubber doesn’t work that way. Instead, a stretched rubber band mainly has less entropy than an unstretched one—and this too can cause a force.

You see, molecules of rubber are like long chains. When unstretched, these chains can curl up in lots of random wiggly ways. ‘Lots of random ways’ means lots of entropy. But when you stretch one of these chains, the number of ways it can be shaped decreases, until it’s pulled taut and there’s just one way! Only past that point does stretching the molecule take a lot of energy; before that, you’re mainly decreasing its entropy.

So, the force of a stretched rubber band is an entropic force.

But how can changes in either energy or entropy give rise to forces? That’s what I want to explain. But instead of talking about force, I’ll start out talking about pressure. This too arises both from changes in energy and changes in entropy.

Entropic pressure — a sloppy derivation

If you’ve ever studied thermodynamics you’ve probably heard about an ideal gas. You can think of this as a gas consisting of point particles that almost never collide with each other—because they’re just points—and bounce elastically off the walls of the container they’re in. If you have a box of gas like this, it’ll push on the walls with some pressure. But the cause of this pressure is not that slowly making the box smaller increases the energy of the gas inside: in fact, it doesn’t! The cause is that making the box smaller decreases the entropy of the gas.

To understand how pressure has an ‘energetic’ part and an ‘entropic’ part, let’s start with the basic equation of thermodynamics:

What does this mean? It means the internal energy of a box of stuff changes when you heat or cool it, meaning that you change its entropy but also when you shrink or expand it, meaning that you change its volume Increasing its entropy raises its internal energy at a rate proportional to its temperature Increasing its volume lowers its internal energy at a rate proportional to its pressure

We can already see that both changes in energy, and entropy, can affect Pressure is like force—indeed it’s just force per area—so we should try to solve for

First let’s do it in a sloppy way. One reason people don’t like thermodynamics is that they don’t understand partial derivatives when there are lots different coordinate systems floating around—which is what thermodynamics is all about! So, they manipulate these partial derivatives sloppily, feeling a sense of guilt and unease, and sometimes it works, but other times it fails disastrously. The cure is not to learn more thermodynamics; the cure is to learn about differential forms. All the expressions in the basic equation are differential forms. If you learn what they are and how to work with them, you’ll never get in trouble with partial derivatives in thermodynamics—as long as you proceed slowly and carefully.

But let’s act like we don’t know this! Let’s start with the basic equation

and solve for First we get

This is fine. Then we divide by and get

This is not so fine: here the guilt starts to set in. After all, we’ve been told that we need to use ‘partial derivatives’ when we have functions of several variables—and the main fact about partial derivatives, the one that everybody remembers, is that these are written with with curly d’s, not ordinary letter d’s. So we must have done something wrong. So, we make the d’s curly:

But we still feel guilty. First of all, who gave us the right to make those d’s curly? Second of all, a partial derivative like makes no sense unless is one of a set of coordinate functions: only then we can talk about how much some function changes as we change while keeping the other coordinates fixed. The value of actually depends on what other coordinates we’re keeping fixed! So what coordinates are we using?

Well, it seems like one of them is and the other is… we don’t know! It could be or or or perhaps even This is where real unease sets in. If we’re taking a test, we might in desperation think something like this: “Since the easiest things to control about our box of stuff are its volume and its temperature, let’s take these as our coordinates!” And then we might write

And then we might do okay on this problem, because this formula is in fact correct! But I hope you agree that this is an unsatisfactory way to manipulate partial derivatives: we’re shooting in the dark and hoping for luck.

Entropic pressure and entropic force

So, I want to show you a better way to get this result. But first let’s take a break and think about what it means. It means there are two possible reasons a box of gas may push back with pressure as we try to squeeze it smaller while keeping its temperature constant. One is that the energy may go up:

will be positive if the internal energy goes up as we squeeze the box smaller. But the other reason is that entropy may go down:

will be positive if the entropy goes down as we squeeze the box smaller, assuming

Let’s turn this fact into a result about force. Remember that pressure is just force per area. Say we have some stuff in a cylinder with a piston on top. Say the the position of the piston is given by some coordinate and its area is Then the stuff will push on the piston with a force

and the change in the cylinder’s volume as the piston moves is

Then

gives us

So, the force consists of two parts: the energetic force

and the entropic force:

Energetic forces are familiar from classical statics: for example, a rock pushes down on the table because its energy would decrease if it could go down. Entropic forces enter the game when we generalize to thermal statics, as we’re doing now. But when we set these entropic forces go away and we’re back to classical statics!

Entropic pressure—a better derivation

Okay, enough philosophizing. To conclude, let’s derive

in a less sloppy way. We start with

which is true no matter what coordinates we use. We can choose 2 of the 5 variables here as local coordinates, generically at least, so let’s choose and Then

and similarly

Using these, our equation

becomes

If you know about differential forms, you know that the differentials of the coordinate functions, namely and form a basis of 1-forms. Thus we can equate the coefficients of in the equation above and get:

and thus:

which is what we wanted! There should be no bitter aftertaste of guilt this time.

The big picture

That’s almost all I want to say: a simple exposition of well-known stuff that’s not quite as well-known as it should be. If you know some thermodynamics and are feeling mildly ambitious, you can now work out the pressure of an ideal gas and show that it’s completely entropic in origin: only the first term in the right-hand side above is nonzero. If you’re feeling a lot more ambitious, you can try to read Verlinde’s papers and explain them to me. But my own goal was not to think about gravity. Instead, it was to ponder a question raised by Allen Knutson: how does the ‘entropic force’ idea fit into my ruminations on classical mechanics versus thermodynamics?

It seems to fit in this way: as we go from classical statics (governed by the principle of least energy) to thermal statics at fixed temperature (governed by the principle of least free energy), the definition of force familiar in classical statics must be adjusted. In classical statics we have

where

is the energy as a function of some coordinates on the configuration space of our system, some manifold But in thermal statics at temperature our system will try to minimize, not the energy but the Helmholtz free energy

where

is the entropy. So now we should define force by

and we see that force has an entropic part and an energetic part:

When the entropic part goes away and we’re back to classical statics!

---

I’m subject to the natural forces. – Lyle Lovett

Thanks to astronaut Ron Garan on Google+, I was alerted to some amazing footage of the Moon setting as seen by astronauts on board the International Space Station. I uploaded it to YouTube and added some comments to show you something really cool…

[Set it to high-def and make it full screen!]

Astonishing, isn’t it? As the Moon sets, you’re seeing it through thicker and thicker air. The air acts like a lens, bending the light upward. The part of the Moon nearer the Earth’s limb gets bent up more, so the Moon looks like it’s getting flattened. Watch it again; the top of the Moon doesn’t appear to be affected much. It looks more like the bottom slows down and the top pushes into it. You can read about this effect in more detail in an earlier blog post.

Weirdly, as I watched the video, it looked very much like the whole Moon was shrinking as it set, as if it were receding rapidly. When I saw that I knew intuitively that couldn’t be real; the ISS is only moving a few thousand kilometers over the time this whole video was taken (about ten minutes), not nearly enough to see that big a change in the size of the Moon. It’s 400,000 kilometers away, after all! So I measured the size of the Moon on the screen, and incredibly the width doesn’t change. Do you see it appear to shrink too? It’s an illusion!

Funny how our brain interprets such things. As if seeing a gigantic rock moving through the sky while perched on board a football-field sized satellite moving at 30,000 km/hr isn’t weird enough!

Credit: Image Science and Analysis Laboratory, NASA-Johnson Space Center. "The Gateway to Astronaut Photography of Earth".

---

Related posts:

- The Moon is flat!
- The twice reflected Moon light
- Incredible time lapse: Milky Way over Africa

This week I’m on tour, giving the annual Tyndall lecture of the Institute of Physics to secondary school students. Yesterday I gave two lectures at University College Cork, today I was in the University of Limerick, tomorrow I’ll be at NUI Galway and on Friday I’ll be talking in Queen’s University Belfast. The biggest event is a set of twin lectures in the main hall of the RDS in Dublin on Thursday.

I decided to give a talk titled ‘The big bang – is it true?’ because this is the question I am most frequently asked. It is also the title of my book-in-progress so the tour is a good dummy run (I gave a similar talk to the Graduate School of Arts and Sciences at Harvard last year).  The abstract can be found on the poster below and the slides are on my Seminars Page.

Tyndall 2012 poster

So far, the lectures are good fun. I address the question by giving a brief overview of the main experimental discoveries that underpin the big bang model, with a little bit of theory along the way. I also explain the main flaws of the model, not least the problem of the singularity (while we have a highly successful model of the evolving universe from its first moments, we have no knowledge of the bang itself, or even know if there was a bang. Nor will we, until we learn how gravity, space and time behave on the quantum scale). I am constantly amazed by the number of scientists who are unaware of this problem.

There are always plenty of questions afterwards. I enjoy this part the most, it’s astonishing how the same questions come up agin and again. What happened before the bang? What is outside the universe? How will it end? All in all, the tour is great fun if a little tiring – a lot of traveling and searching for lecture rooms and hotels.

I’m also becoming an expert on university campuses in Ireland. My favourite so far is University College Cork. Beautiful, old and tiny, it is nicer again than Trinity College Dublin. On the other hand, the University of Limerick is very like University College Dublin with its fantastic grounds and playing fields.

Meanwhile, the future of my own college (Waterford Institute of Technology) remains uncertain. Local interests have been campaigning for many years for a regional university and it is true that the city and surrounding regions have suffered by not having a university. (The best and the brightest school-leavers head to college in Cork and Dublin and don’t come back – not to mention the problems in attracting industry to the region). As WIT is respected academically for its research output, there is now a strong political wind to upgrade the college to university status. However, the proposed upgrade has triggered a campaign to amalgamate and upgrade all the Institutes of Technology to university status. Like many academics, I think this would be a pity because the binary system of universities and Institutes has served Ireland very well (the latter are of slightly lower standard and more practical bent). So it’s a tricky situation, hard to know what the best solution is..

Update

Galway was fun, but the lectures in the Royal Dublin Society were hard work. A huge venue, it was difficult for students to ask questions afterwards. They seemed to enjoy the talk but I missed the usual interaction. Belfast tomorrow and then I’m heading homewards…

Here are two of the top prize winners in the competition (see earlier posts for the others, and for the full list). The 2nd Prize and 3rd Prize winners are below! Consider watching them in full HD. (Sadly, the 1st Prize winner, Time, (by Kevin Le and Edward Saavedra) uses copyrighted music and they are [...]

The work which I am going to talk about, Large Nongaussianity in Axion Inflation, is written in collaboration with Marco Peloso. (In case you want more information about this work, we’ve released a long follow-up paper with Ryo Namba, and my website also contains some material.) I’ve split the discussion below into two parts. In the first part I try to provide some context for the work and give a sense of the key implications of our results, some of which I think transcend the specific model that we consider. The second section is a somewhat more technical discussion of the key physics and observational signatures of the model.

1. Probing Inflaton Interactions with the CMB

What can be gleaned about microscopic particle physics by studying the large scale structure of our universe? At first glance, the question might seem surprising. However, in recent years the interface between cosmology and high energy particle physics has been a vibrant and active field of research. In part, this interaction has been driven by the idea that the observed large-scale cosmological perturbations in our universe originate from quantum mechanical processes. According to the dominant paradigm, the very early universe underwent a prolonged phase of rapid expansion called inflation during which the quantum fluctuations of a spin-0 particle (the inflaton) were stretched to cosmological size and imprinted on the large-scale geometry of space-time. These fluctuations provide the seeds for structure formation and may be probed in the contemporary universe by Cosmic Microwave Background (CMB) and Large Scale Structure (LSS) observations. Although we’re still eagerly waiting for the “smoking gun” confirmation of this scenario (most likely in the form of a detection of primordial gravitational waves), the data nevertheless seem consistent with the idea that inflation occurred.

 

For me, a big part of the excitment surrounding this idea is that the dynamics of the very early universe seem to have involved particle physics in very extreme conditions. The characteristic energy scale associated with inflation is many orders of magnitude higher than what is accessible in particle accelerators. Moreover, the transistion from inflation to the conventional hot big bang may have been characterized by violent instabilities and turbulent, nonlinear dynamics of quantum fields far from equilibrium. The microphysics underlying these extreme moments in the early history of our universe may have left observable imprints in the CMB, LSS and also relic gravitational waves. In this way, there is a possibility that cosmological observations might teach us something about fundamental particle physics in a regime that will probably never be accessible in the laboratory.

A key question is how the inflaton “fits in” with the rest of particle physics. What are the properties of this new particle? How does it interact with other particles in nature? I will argue that valuable clues may be encoded in the statistical distribution of CMB fluctuations, specifically departures from gaussianity. Cosmological nongaussianity has attracted a lot of interest over the last few years. This excitement, I think, is well justified. Nongaussian statistics encode a wealth of detailed information about the physics of the early universe. Moreover, this excitement is timely: nongaussianity will be probed to unprecedented accuracy with the recently-lauched Planck satellite.

What level nongaussianity should be expected for reasonable microscopic models of inflation? Most cosmologists would say “not very much”; it is usually claimed that the simplest models of inflation predict a level of primordial nongaussianity that is too small to be resolved with Planck. Indeed, nongaussianity is sometimes touted as a “smoking gun” signal for non-standard inflationary dynamics. Very roughly, the argument goes like this: nongaussianity is a measure of the strength of interactions, however, the kind of theories that leads to inflation are almost always very weakly interacting. (Getting a bit more technical: slow roll inflation requires extremely flat scalar potentials which, in turn, implies that interactions are weak and nongaussianities are small.) In order to circumvent this “no go” argument previous studies have invoked a variety of novel effects including strong dissipation, higher derivatives and small sound speed. These are all very interesting ideas and I’ve worked on some of them myself. However, I think it’s fair to say that many of the models on the market which predict large nongaussianity are somewhat unorthodox.

My recent paper, written in collaboration with Marco Peloso, challenges the conventional lore. We have found that the simplest and most natural particle physics models of inflation can easily lead to an observable nongaussian signal and are, in fact, already constrained by observation! In this recent work we rely on a very simple loophole to the “no go” argument presented above: that chain of logic only applies to self-interactions of the inflaton particle. On the other hand, one generically expects that the inflaton should couple not just to itself but also to other particles in nature. (Indeed, this is probably necessary in order to successfully recover the hot big bang after inflation.) Such interactions are almost always ignored, however, it turns out that their consistent inclusion can have a radical impact on the observational predictions of a model. The reason these interactions can be so important has to do with a novel effect — nonperturbative particle production — that I’ll discuss in more detail shortly.

The idea that particle production during inflation might lead to interesting phenomenology was also the subject of my last posting on NEQNET. In my recent paper, we consider a qualitatively similar effect which can arise in a very natural way. We work in the context of a popular and theoretically appealing class of inflation models and show how consistent inclusion of the interactions between the inflaton and spin-1 particles very naturally leads to large nongaussianity. Part of what I find exciting about this model is its simplicity: we don’t require any “extra” structure or unnecessary complication in model-building in order to get an interesting phenomenology. In terms of the bigger picture, I think the message to take away from these kinds of studies is the following: large nongaussianity is probably much more generic than has previously been thought. Personally, I find this very encouraging. If we are lucky enough to detect this kind of effect, it may provide us with valuable clues about how the inflaton “fits in” with the rest of particle physics.

2. Axions, Inflation and Particle Production

As I mentioned above, slow roll inflation requires extremely flat scalar field potentials. Flat potentials are notoriously sensitive to UV physics and hence we are faced with a serious technical fine tuning problem. There are a number of possible solutions, however, one of the most cogent idea is to suppose that the inflaton is an axion. Axions are characterized by a softly broken shift symmetry which protects the potential from large corrections that might otherwise spoil inflation. This simple idea provides a very natural way to implement inflation in a controllable effective field theory. Moreover, axions are ubiquitous in particle physics: they can arise whenever an approximate global symmetry is spontaneously broken and are plentiful in string theory models.

The first axion inflation model was proposed by Freese, Frieman and Olinto in 1990 and dubbed “Natural Inflation”. The original model involved a super-Planckian decay constant and might be impossible to embed in a sensible UV theory. Happily, it turns out that there are plenty of ways to make axion inflation work with sub-Planckian decay constant! (Some popular examples including N-flation and axion monodromy.) Our results apply to a huge variety of particle physics models of axion inflation.

For our mechanism, the important thing is how axions couple to spin-1 gauge fields. In any axion inflation model, there must generically be present a pseudo-scalar coupling of the form:

In the perturbative regime, this interaction can be represented by a diagram like the one below, that couples the inflaton field to two gauge bosons. (I should stress that the gauge boson in question here might be the usual standard model photon, or it might be some hidden sector field. Our analysis works in either case.)

This kind of interaction vertex is a very generic feature of what are perhaps the most natural particle physics models of inflation. Therefore, it makes sense to ask what are the implications of this interaction for the cosmological predictions of the model. We weren’t the first group to think about this, in a very interesting work Anber and Sorbo noticed that, at very strong coupling, this interaction could help to slow the motion of the inflaton via dissipation. The approach that Marco and I took is somewhat more conservative. We noticed that this interaction can dramatically modify the phenomenology of the model even in the conventional slow roll regime.

The underlying physics is as follows. During inflation the axion forms a homogeneous, classical condensate. Gauge bosons propagating in this background condensate experience a modified dispersion relation: instead of the usual E=p that one expects for a massless particle, there is a new contributions which depend on the dynamics of the inflaton. The effect of this modified dispersion relation is to induce an exponential growth for one of circular polarization modes of the gauge field. This can be interpreted as gauge particle production and is very similar to tachyonic preheating (however, I must stress that we’re talking about particle production during inflation).

So far, we have established that the dynamics of the homogeneous inflaton lead to copious production of gauge quanta, via the usual pseudo-scalar interaction that is unavoidable in any axion inflation model. What is the fate of this produced gauge particles? The interaction vertex above can describe inverse decay, a process in which two gauge quanta “merge” to produce an inflaton particle. (You get this from the diagram above with time running from right to left.) Inverse decay processes provide a new source of cosmological perturbations, complementary to the usual quantum vacuum fluctuations of the inflaton. Remarkably, this new source of perturbations can actually dominate in the regime where the decay constant is sub-Planckian (which is where the effective field theory is under control). It is interesting that, although the general idea of axion inflation is more than 20 years old, this important source of cosmological perturbations has only recently been accounted for.

The main result of my recent paper is to note that the phenomenology of axion inflation is radically modified when particle production and inverse decay are taken into account. Firstly, the fluctuations generated by inverse decay are highly nongaussian. We find that a large (nearly) equilateral shape nongaussianity is easily generated. In fact, the WMAP7 limit on nongaussianity already implies a nontrivial bound on the axion decay constant. The second interesting prediction is a violation of the usual consistency relation for the tensor-to-scalar ratio. This arises because the produced gauge quanta contribute to the anisotropic stress tensor and thus source gravitational waves. In the most interesting regime of parameter space, it turns out that this latter effect is small. Hence, the generic expectation for axion inflation is large equilateral nongaussianity along with the same value of spectral index and tensor-to-scalar ratio as in chaotic inflation. If Planck detects this type of nongaussianity, then we will have an indirect measurement of the inflaton coupling to gauge fields. If Planck sees nothing, then we will have a surprisingly stringent bound on this same coupling.

To sum up: in a given microscopic realization of inflation, there will typically be some couplings between the inflaton and other particles in nature. The specific form of these interactions depends on how the inflaton “fits in” with the rest of particle physics. What we have found is that very simple kinds of interactions in well-motivated models of inflation can lead to surprisingly rich particle production dynamics. These, in turn, give rise to novel observational signatures, most notably large nongaussianity. Moreover, this subject is just the beginning to be explored, I expect that a rich variety of qualitatively similar effects may be possible in all sorts of simple models. It may be time to re-think the lore that observable nongaussianity cannot be obtained in simple, natural models of slow roll, single field inflation.

Post from: NEQNET: The world of theoretical physics

Large non-Gaussianity from axion inflation

I’ve spent nearly all day getting my notes ready to start teaching Accidental Raunchy Slippers  Nuclear and Particle Physics tomorrow to the massed ranks of Third-Year Physics students here in the School of Physics & Astronomy at Cardiff University. I’ve drawn so many Feynman diagrams in the last couple of days that I’ve started to see them everywhere I look, even in entirely unexpected contexts, as in this example from the excellent PHD Comics…

Follow @telescoper

Most Fermilab personnel have learned to ignore the ubiquitous booms, hums, growls and crackles of Fermilab machinery. But composer Mason Bates places these sounds center stage in his new piece "Alternative Energy."

Last week I spent a few interesting days in the pleasant winter setting of Engelberg, a mountain location in the Swiss alps. There I attended the CHIPP 2012 winter school, an event organized by Vincenzo Chiochia and Gabriella Pazstor from University of Zurich. They invited me to give a three-hour mini-course in Statistics for data analysis in High-Energy Physics, something which was a new experience for me. It took me the best part of the last couple of months to get prepared, but I was glad I did. In the end, the material I put together could have been used profitfully for five or six hours of lecture, but by skipping some of the topics I could get to the end without using a silly speed.

read more

Now, let us start with a look at the different methods in more detail. The first is the mainstay of theoretical physics, and the first thing everyone tries when encountering or designing a new theory: Perturbation theory, often abbreviated simply by PT.

The basic idea of perturbation theory is rather direct. When we have a theory, it is very often the case that we can solve a simpler version of it exactly. For example, if we have QED then we can solve exactly the case where the electromagnetic charge would be zero, because the particles then do not interact with each other. And free, non-interacting particles is something we can do very well. Of course, this is not what QED is really like. Otherwise, we could not see, as the electrons in our eyes would not react to the light made out of photons. To capture this, perturbation theory assumes that the interactions between electrons and photons is only a small alteration to the picture of free particle: A perturbation, and hence the name. Of course, finding a useful split depends on the theory in question, and many different types are actually in use.

Once such a setup is available, we have created powerful mathematical tools how to calculate then anything we want under this assumption. The most important principle is that we can reformulate what we mean by perturbation mathematically by stating that some quantity is small What this precisely means depends on the theory in question. In the above example of QED, it would be the electric charge.

We can then organize perturbation theory systematically by counting how often the small quantity appears in an expression. We then speak of the order of perturbation theory. If it appears the lowest possible number of times, which may be zero, we call this tree level. The reason for this name is that the mathematical expressions can be generated in the way a tree grows, i.e., in the form of starting somewhere and then moving on. In fact, in general this is often equivalent to a classical theory. This means that we treat the particles as quantum particles, but the interaction between them like a classical interaction, without additional quantum effects.

We can now increase the number of times the quantity appears. We also say that we calculate higher orders in the quantity, where order counts the number of times the quantity appears. If we calculate the contribution with the second-least number of times the quantity appears, we call this leading order correction. Since such a correction only appears in the quantum theory, we also call it a quantum correction. The contribution with third-least appearance is called next-to-leading order. If we further increase the order, we just add the corresponding number of times next-to in front, e.g. next-to-next-to-next-to-leading order. This seems to become quickly awkward, but no fear, no too high orders are often calculated.

The reason is that perturbation theory at higher order becomes rather complicated just from an organizational point of view. Quickly, perturbative expressions fill hundreds and thousands of pages with expressions, which have to be evaluated. The final end result will only fill a very few pages, if more than one at all. Over the time, we have developed very powerful methods to deal with this complexity. If you ever heard of Feynman diagrams, given that these have made their way even into some obscure corners of pop culture, then this is one of these tools. Its a very powerful graphical technique to organize perturbation theory in a very efficient way. And this is quite important. There are furthermore other ingenious methods to reduce the amount of calculations necessary. Nonetheless, in the end the expressions remain rather long, and it requires computers to evaluate them. This is in general straightforward to tell the computer what to do. But it is very challenging to do it in a way that the computer is not occupied for the next couple of years, but only a few days or less.

With these methods, we have went to order ten in QED, and for some quantities to order four in the standard model. This seems little, but because of the complexity required many people and decades of time. Still, some times experiments are so precise that the accuracy achieved by these calculations is not sufficient. But of course, there are also many cases where it is the other way around. In a way, it is a kind of arms race between theoreticians and experimentalists.

In the end, however, perturbation theory will not give you the full answer. You can mathematically prove that certain phenomena cannot be calculated using perturbation theory. You may be lucky, and using a different starting point, this can be circumvented for a certain quantity, but then other quantities will not be possible to access. Furthermore, we know that perturbation theory cannot be pursued to arbitrary order, but will collapse at a certain point, for mathematical reasons. Though also here progress has been made, we know that perturbation theory cannot provide the full answer to any question. Already as simple a quantity as the mass of the proton cannot be calculated in perturbation theory. Nonetheless, much of what we measure in experiments, say at LHC, can be very well and very accurately calculated with perturbation theory. Thus, perturbation theory remains to be one of the main tools in particle physics, and for very good reasons so.

After having fixed the definition of the extended Itō integral, I have posted a revised version of my paper on arXiv (see here). The idea has been described here. A full account of this story is given here. The interesting aspect from a physical standpoint is the space that is fluctuating both for a Wiener process and a Bernoulli process, the latter representing simply the tossing of a coin. We can sum up everything in the very simple formula

The constant to be properly fixed to recover Schrödinger equation.

Marco Frasca (2012). Quantum mechanics is the square root of a stochastic process arXiv arXiv: 1201.5091v2

Filed under: Mathematical Physics, Physics, Quantum mechanics Tagged: Itō calculus, Stochastic processes

The pattern of calls and texts between humans reveals how women invest more heavily in their main relationship than men; and how this changes as they age.

Various studies have shown that the frequency of contact between individuals is a reliable indicator of the emotional link between them. So it should come as no surprise that the data from mobile phone calls is a potential treasure trove of information about the social lives of humans. 

But analyses of this data so far have been distinctly unspectacular. For example, the location data associated with phone calls has revealed various new intricacies in the movements of commuters. Interesting but hardly jaw-dropping.

That is set to change with the work of Vasyl Palchykov at the Aalto University School of Science in Finland and a few buddies including a couple of old hands in the form of Albert-László Barabási at Northeastern University and Robin Dunbar at the University of Oxford (of Dunbar's number fame). 

These guys have got hold of a corpus of mobile phone data relating to calls between 1.4 million women and 1.8 million men in an unspecified European country. Between them, these phone subscribers made almost 2 billion calls and sent almost half a billion text messages. In addition to the gender of each subscriber, Palchykov and co also managed to get their age as well. 

That's significant because it allows them to study not allow the pattern of calls between genders but the way this changes with age. 

They began by taking each subscriber and determining the age and gender of the person they werein contact with most frequently, second most frequently and so on. These, they assume, are the 'best' friend, second best friend and so on.

Then, they looked at how the 'best friends' changed as subscribers age. It turns out in general that between the ages of 18 and 40 or so, men and women have best friends of the opposite sex. Palchykov and co assume this reflects the general pattern of mating in society. Second best friends are generally of the same sex at this age.

But they tease the most interesting phenomena out of the fine detail in their dataset. They conclude for example that women are more focused on opposite-sex relationships than men are during the period of their lives when they are reproductively active. That indicates that women invest  more heavily in creating and maintaining their relationships than men.

As women age, their attention shifts from their spouse to younger females some 25 years or so younger. That's about equal to a generation gap and Palchykov and co assume these younger females are daughters. This attention shift also seems to equate to the arrival of grandchildren, when the older female again once again begins to invest more heavily.

While older women focus more heavily on younger females, older men maintain an even gender balance in the second best friends, presumably this reflects an equal attention between children of opposite sexes.

What's striking about this is how strongly female relationships are determined by their reproductive cycle. “Women’s gender-biases thus tend to be stronger than men’s, seemingly because their patterns of social contact are strongly driven by the changes in the patterns of reproductive investment across the lifespan,” say Palchykov and co.

Clearly, female reproductive strategies change more explicitly as they age, switching from mate choice to personal reproduction to parental investment and finally grandparental investment, particularly after they reach 40. 

However, the most dramatic conclusion from this work is about the pattern of social relationships that play the most important role in society. Palchykov and co say the tendency in the past has been to assume that father-son relationships dominate. 

By contrast, “our results tend to support the claim that mother-daughter relationships play a particularly seminal role in structuring human social relationships,” they say. 

This difference on the way the sexes invest in relationships is exactly what evolutionary biologists expect. But although previously suspected, it has proved particularly difficult to test. That's why this work is something of a landmark.

Clearly, the ability to study human relationships on such a vast scale opens up a host of new avenues for research in social and reproductive strategies.

In particular, this study looks only at the existence of links between people, not the the directional asymmetries in relationships or who initiates contact.  Palchykov and co leave that for another day.

There's a mountain of data ready to be mined on this. And clearly, there's gold in them thar hills.

Ref: arxiv.org/abs/1201.5722: Sex differences in intimate relationships 

As of this minute, 1890 scholars have signed a pledge not to cooperate with the publisher Elsevier. People are starting to notice. According to this Wired article, the open-access movement is “catching fire”:

• David Dobbs, Testify: the open-science movement catches fire, Wired, 30 January 2012.

Now is a good time to take more substantial actions. But what?

Many things are being discussed, but it’s good to spend a bit of time thinking about the root problems and the ultimate solutions.

The world-wide web has made journals obsolete: it would be better to put papers on freely available archives and then let boards of top scholars referee them. But how do we get to this system?

In math and physics we have the arXiv, but nobody referees those papers. In biology and medicine, a board called the Faculty of 1000 chooses and evaluates the best papers, but there’s no archive: they get those papers from traditional journals.

Whoops—never mind! That was yesterday. Now the Faculty of 1000 has started an archive!

• Rebecca Lawrence, F1000 Research – join us and shape the future of scholarly communication, F1000, 30 January 2012.

• Ivan Oransky, An arXiv for all of science? F1000 launches new immediate publication journal, Retraction Watch, 30 January 2012.

This blog article says “an arXiv for all science”, but it seems the new F1000 Research archive is just for biology and medicine. So now it’s time for the mathematicians and physicists to start catching up.

In almost any project, the path between “a good idea” and the “final exciting result” contained a proposal. It may have been a proposal to obtain access to scarce resources (like telescopes or accelerator beams), or it may be have been a proposal to obtain other more prosaic resources (i.e., money, to pay for the needed personnel and supplies). Whatever the nature of the proposal, however, I guarantee that the competition was ridiculously stiff, and that the odds of having any given proposal accepted were quite low (for reference, in most astronomy contexts, over-subscription rates tend to be factors of 5-10). These unfavorable odds can be incredibly demoralizing. They also can have profoundly negative impacts on a talented scientist’s career, if the odds never manage to tip in their favor.

Given the inspiration of the looming Hubble Space Telescope deadline, I thought I would share some of my “big picture” views on crafting successful proposals, expanding significantly on the more succinct advice given in an earlier post. While I’ve developed these opinions based on my experience in astronomy, I suspect they’d apply to many other fields, both within and beyond science. So here goes…

A Proposal is a Highly Structured Rigorous Argument

In its most abstract form, a proposal is a piece of persuasive writing that lays out a convincing case that the proposed research is:

1. important
2. feasible
3. efficient

By “important”, I mean that the project must rise above the level of “good to do”, and instead be seen as “must be done”, even by people who don’t work in the field. By “feasible”, I mean that there must be a clear path to a definitive scientific result. By “efficient”, I mean that the particular approach you’ve taken is the optimal one for reaching the important goals you’re targeting (i.e. aim for “Studying X provides the cleanest test of Important Science Y” and avoid building a proposal to study X when studying Z is clearly a more direct approach to Important Science Y — even if you worked on X for your thesis.)

You should lay out your arguments for Every. Single. One. of these cases before you write a single word of latex. Why? Because proposals live or die not on the beauty of your prose, but on the structure of your argument. If the reviewer does not believe that you’ve made the case for importance, feasibility, and efficiency, you’re done.

Here’s how I do this. Although I’m sure it will seem remedial to many of you, and reveal me as the anal geek that I am, I start a stupid ASCII file with two sections:

1. Selling Points
2. Potential Weaknesses to Shore Up

I then start filling out each with short bullet points listing every possible argument for or against what I’m proposing.

The selling points should be fairly easy, since you’re likely to write proposals for things you are inclined to think are awesome. Do, however, avoid the pitfall of conflating “important to me” with “important to Science”. Just because you would really like to know more about some property of something you’re interested in, doesn’t mean that other people will naturally share your enthusiasm. Keep your eye on the big picture.

The “Potential Weaknesses” section can be a bit trickier, since you need to channel your inner crabby reviewer. Think of every nit-picky, outside the box criticism one could throw at your idea, and every area where a reviewer could get confused. (As an example, here’s a list of some of the self-criticisms I came up with for an HST proposal for NIR observations of nearby galaxies a few years back: “What about AO from the ground?” “Why this many targets — how many do you actually need?” “What about dust (i.e. is 1 NIR filter OK)?” “Are the models really in need of improvement?” “How can we claim to do galaxy science while simultaneously arguing that the models aren’t yet up to it?” “Are the results confused depending on fraction of O-rich vs C-rich AGB?” etc).

In short, the “Selling Points” section is about demonstrating “importance”, and the “Potential Weaknesses” section is about assessing “feasibility” and “efficiency”.

After you’ve got an initial list, you have to step back, evaluate, and edit.

• Go through the selling points and prioritize. Decide what the “main message” of your proposal is, based on which bullet points speak most effectively to the larger importance of what you’re proposing. If your ideas are strong, you’ll usually find that several of the most compelling bullet points will group together and can be ordered to tell a single story. You’ll also find that some of the bullet points will not naturally fit within that narrative. Identify this subset of arguments that are “nice, but not compelling”. You’ll want to be sure to minimize these in the proposal, to avoid their distracting from a more central idea. I speak from experience when I say that you really do not want to confuse the reviewers about what your proposal is about (i.e. It’s better to have something like “Dark Matter! Dark Matter! Dark Matter! and by the way it also tells you something about planets, frogs, and quark stars” rather than “Dark Matter! Planets! Frogs! Quark Stars!”, since the latter leads to complaints from the reviewers that while they believed your dark matter ideas, you had not fully fleshed out a compelling case for the frog science.)
• For each entry in the “Potential Weakness” section, write down any brief ideas about addressing those concerns (something like “Make figure showing evolution of models with time” “Check number of stars expected and compare to sizes of Galactic samples”, etc). You don’t have to come up with definitive answers, but you should lay out a road map for what you need to do to make your experiment look feasible and efficient.

At this point, I sometimes make a third section and list a few figures that seem like they support the key scientific ideas, or that shore up some of the obvious weaknesses.

Now that you have this silly little ASCII file (which you shouldn’t spend more than a day on, if that), send it to your collaborators. Get their feedback about what they think the strongest selling points are, what their additional concerns are, and what arguments they would use to shore up weaknesses. Expand the file accordingly, so you have a record of everything that you think needs to go into the proposal. You’ll probably find that it’s a huge time savings to get this to your collaborators in this form, before you have a 10 page latex file with embedded figures. If you do the latter, your collaborator will likely come back and say “You know, I think the reviewers are going to be way more interested in frogs”, at which point you have to chuck out weeks of work. With this method, you get feedback quickly (since they have to skim a very short list of bullet points), and you don’t have a lot of sunk costs if you decide to overhaul the arguement.

At this point you’ll have a document that summarizes your rhetorical argument. Your case will be laid out so that you can easily evaluate it on its scientific merits. So, before you dive into writing, you need to step back and decide if you’ve actually constructed a strong case. Sometimes, it will become obvious that there are too many weaknesses to address, and that it’s going to be an uphill battle to convince anyone that this needs to be done. If that’s the case DON’T WRITE THE PROPOSAL! I have probably a half dozen of these ASCII files where I spent half a day deciding that I didn’t, in fact, have a compelling project, and I’d be better off investing my time elsewhere. That’s OK! The exercise of structuring your argument first is designed to be fast, so you don’t sink much time in before you decide whether to continue or not.

Once you (and your collaborators) are convinced that you do in fact have a strong case, you need to start building the actual text. I frequently will estimate the number of paragraphs I expect to have for my scientific justification (usually 2.5-3 per page), and then make an enumerated list showing how the argument will flow through the paragraphs. This exercise helps to keep the text following the structure of the argument, so that it builds to make the main points. It also helps me to figure out when I’m trying to cram too much information in.

If you’ve gone through all of the above, you’ll find that the proposal will almost write itself. You will have cleanly separated “generating text” from “generating a compelling project”, such that you know exactly what you want to convey, and what the text needs to accomplish. Generating lovely English sentences at this point is much easier.

I just heard about the movement to Boycott Elsevier journals when reading Sean Carroll's blog.

Certainly the success and failure of a peer-reviewed journal depends very much on the participation of scientists, both in terms of submitting good work for publication, and for refereeing these submissions. So if this movement catches on, Elsevier would certainly be faced with quite a challenge.

In my current position, the only Elsevier journal that would be affected is the Nuclear Instrumentation and Method - A. In my "previous life" as a condensed matter physicist, I would say Physica B and Physica C, but not anymore.

So this "boycott" probably won't be affecting us that much since we can certainly bypass NIM-A for other journals.

But what about you? If you are a practicing scientist and you do send work to be published in an Elsevier journals, would you stop doing that? Would you also stop refereeing for an Elsevier journal?

Zz.

In 1931, Wolfgang Pauli went for a long-term stay to Ann Arbor, Michigan. In Ann Arbor, Pauli gave lectures and met, among others, with Otto Laporte, George Uhlenbeck and Arnold Sommerfeld. In the summer 1931, the USA suffered from heat and prohibition. In a letter from July 1st, 1931 to his student Rudolf Peierls, Pauli wrote:

"[T]rotz Gelegenheit zum Schwimmen leide ich sehr unter der großen Hitze hier. Unter der "Trockenheit" leide ich aber gar nicht, da Laporte und Uhlenbeck ausgezeichnet mit Alkohol versorgt sind (man merkt die Nähe der kanadisehen Grenze). Physik (und Physiker) gibt es hier sehr viel, aber ich finde sie zu formal..."

"Despite the opportunity to swim, I suffer from the heat. I do not suffer however from the "dryness," since Laporte and Uhlenbeck have an excellent supply of liquor (one notices the vicinity of the Canadian border). One finds here a lot of physics (and physicists), but most I find too formal..."

Evidently, the supply was ample since, in a letter from later that summer, Pauli reported:

"Dummerweise bin ich neulich (in etwas angeheitertem Zustand) so ungünstig über eine Treppe gefallen, daß ich mir die Schulter gebrochen habe und nun im Bett liegen muß, bis die Knochen wieder ganz sind - sehr langweilig."

"Unfortunately, the other day I fell (somewhat tipsy) on the stairs and broke my shoulder. Now I have to lie in bed till the bones have healed - very boring."

Since drinking was illegal, the official reason for his accident was that he slipped on the tiles at the swimming pool. In the image to the right, you see Pauli with his broken shoulder. Click to enlarge. Image source: CERN archive. Text source: "Wolfgang Pauli: Scientific Correspondence with Bohr, Einstein, Heisenberg a.o." Volume II: 1930-1939, edited by Karl von Meyenn, Springer-Verlag (1985).

While I have the blog open, let me throw in a quick two cents to support the Boycott Elsevier movement. As most working scientists know, Elsevier is a publishing company that controls many important journals, and uses their position to charge amazingly exorbitant prices to university libraries — and then makes the published papers very hard to access for anyone not at one of the universities. In physics their journals include Nuclear Physics, Physics Letters, and other biggies. It’s exactly the opposite of what should be the model, in which scientific papers are shared freely and openly.

So now an official boycott has been organized, and is gaining steam — if you’re a working scientist, feel free to add your signature. Many bloggers have chimed in, e.g. Cosma Shalizi and Scott Aaronson. Almost all scientists want their papers to be widely accessible — given all the readily available alternatives to Elsevier (including the new Physical Review X), all we need to do is self-organize a bit and we can make it happen.

I’ve mentioned before that one of the great pleasures of working in high-energy physics is its international nature. I find the diversity of people and cultures I encounter in the pursuit of knowledge exciting and refreshing.  This week I am visiting the famous Weizmann Institute of Science, outside of Tel Aviv. Many of the physicists in my field who are here or at nearby institutions were in the United States as students, as postdoctoral researchers, or as visitors, at places where I myself was working at one point or another.  Even one of my former students is here.  So there are many old friends and former collaborators in both string theory and particle physics for me to meet with, and to learn from. I’ll also be giving a couple of scientific lectures during this visit.

Meanwhile,  I wanted to mention a mildly interesting article that I happened to notice:

http://news.discovery.com/human/infant-grasp-physics-gravity-law-nature-120125.html

I have nothing negative to say about people doing research into exactly what babies do and don’t have intuition for at various ages, but there are two things I find problematic about the spin that is put on this story.

First, what is striking to me about human babies is not how much they know, but how little, and that point often gets lost in articles whose authors are impressed by how clever babies are. Watch a foal [= a baby horse, for my non-English-speaking readers] stand an hour after birth, and you can see how much intuitive physical understanding most animals are born with. It’s not surprising; they’d die pretty quickly without it.

Meanwhile, the other problem with this story is that knowing that things fall is not in any sense the same thing as knowing about gravity as a law of nature.  On the one hand, every mildly intelligent animal “knows” that things fall (e.g. acorns from trees, balls thrown into the air) except, of course, that birds don’t, and leaves on a windy day often don’t, but hey, who’s counting. And everybody “knows” that lightweight things  (leaves, sheets of paper) fall more slowly than heavy things (rocks, coconuts), though unfortunately this intuition, which everyone has from a young age, happens to be wrong.  As Galileo showed easily, and as you yourself can check easily by putting a coin (or even a small sheet of paper, if you are careful to lay it very flat) on the back of a heavy book and dropping the book, all things fall at the same rate as long as there isn’t air resistance to confuse you. A law of nature is not just a general regularity, such as “things fall”; it is something much deeper, much more precise, and much more subtle than that.

The same goes for solids and liquids; we may recognize that there are objects that prevent our bodies from passing through them, and others that do not, but in what sense is that understanding anything about them?   It’s a statement of “fact”; but facts, even general facts, are not laws.  They are consequences of laws, but they do not by themselves reveal the nature of the law.

What is really at play in the studies of babies’ intuition is that there are some very simple and basic principles of how to interact with the world that you must know if you are to live to the age of three. If you can’t figure out that things fall, you will probably suffer a deadly fall yourself; and if you can’t figure out that there are solids and liquids, you will hurt yourself running into a tree trunk or drown trying to walk across a lake.  You’d also better know quickly that you won’t be able to see in a dark place, and that the leopard that wants to eat you isn’t necessarily gone just because it has disappeared from view.   I’m sorry to say, however, that essential as these survival skills are, they do not count toward a degree in physics.

Filed under: Uncategorized

Apologies that real work (to the extent that what I do can be called “work”) has gotten in the way of substantive blogging. But I cannot resist sharing the amazing things I learned this weekend — amazing to me, anyway, although it’s possible I’m the only one here who wasn’t clued in.

Thing the first is that Morgan Freeman, many years before he went through the wormhole, was a regular on The Electric Company, along with performers like Rita Moreno and Bill Cosby. (Via Quantum Diaries, of all places.) This was public television’s show from the 70′s that was meant for kids who had moved on from Sesame Street — I was more of a Zoom kid myself, but I must have seen Electric Company episodes with Freeman playing hip dude Easy Reader.

Thing the second is that Easy Reader’s theme song, sung in the clip above, is a dead ringer for Amy Winehouse’s “Rehab.” Flip back and forth between playing them if you don’t believe me. So much so, I am told, that DJ’s in clubs will sometimes mix the two tunes together. Not at the clubs I go to, I guess.

Here are the two films that won honorable mentions in the Science Film Competition. Consider watching them in full HD. I’ll release the others tomorrow… Enjoy! -cvj

Our two lovely girls have learned to walk!



Gloria has fallen in love with a plush moose that I bought at the Stockholm airport. When I was pregnant, I gave it to Stefan "for practice," and since then the moose has patiently waited for its cue. It came when Gloria learned to point with her index finger. If her Swedish friend is in sight, she excitedly points and says "Da! Da! Da!" and, if one lets her, she takes the plush moose everywhere.

Lara has learned to drink with a straw, but my efforts to teach Gloria the same have so far been futile. Gloria is generally more picky with things that go into her mouth; she clearly doesn't like vegetables, and every other day refuses to drink juice. On the upside, she has learned that cardboard isn't edible, a lesson that I hope Lara learns before she has eaten up all picture books. We upgraded Lara to the next cloths size; she is now noticeably taller than her sister.

Next week, the babies are scheduled for the meningococcal vaccination, and then we're through with the first round of all the standard vaccinations: diphtheria, tetanus, pertussis, polio, streptococcus pneumoniae, haemophilus influenzae type b, hepatitis b, measles, mumps, rubella and varicella.

I am always shocked when I read about parents who aren't vaccinating their children. I thought that's a problem which exists only in the USA, but our pediatrician puzzled me last year by beginning our first appointment with a forward defense against arguments we hadn't intended to lead.

After some reading, I learned that about 3-5% of Germans believe vaccinations are unnecessary or harmful. UNICEF estimates that in 2009 in Germany the national coverage with the first measles vaccination was 96%. In the USA it was 92%. The basic reproduction number R of measles is estimated to be 12-18. Measles are one of the most contagious diseases known. The percentage of people that have to be immune to prevent a spread of the infection is roughly 1-1/R, for measles that's more than 93%; for mumps and rubella about 80%. However, not everybody who is vaccinated becomes immune.

Too few people know that the reason why the measles, mumps, and rubella (MMR) vaccination is repeated at least once is not that an individual's immunization is improved, but that in at least 5% of all cases the vaccination fails entirely. Our pediatrician said, 5% is what the vaccine producers are claiming, what he sees in practice is 20-30%. One of the probable reasons is that the MMR vaccine has to be kept cold, and any mistake along the delivery line makes the vaccine ineffective. The follow-up vaccination is supposed to bring down the failure rate, 1-(5/100)(5/100) > 0.99, or so the idea. But more realistically 0.96 (1-(20/100)(20/100)) ≈ 92% in Germany, or ≈ 88% in the USA.

And so, measles are far from going extinct and smaller outbreaks still happen. Sadly enough, even in Germany, people still die from measles. The case reported in the article is particularly tragic: A young boy, whose parents refused vaccination, fell sick with measles and, in the doctor's waiting room, infected 6 children, some too young to have been vaccinated; one died.

Ah, I am lecturing again, even though this was supposed to be a family-update post, sorry ;o)

So back on topic, Gloria and Lara had only mild side-effects from the vaccinations. We have exchanged the backward facing baby car seats with forward facing seats, and the girls can now enjoy watching the cars go by, while we can enjoy watching the babies watching. I didn't know how much I hated the backward facing seats till they were gone.

And I should stop referring to Lara and Gloria as "the babies" because they are now officially toddlers.