30 years of Chernobyl disaster April 26, 2016Posted by apetrov in Uncategorized.
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30 years ago, on 26 April 1986, the biggest nuclear accident happened at the Chernobyl nuclear power station.
The picture above is of my 8th grade class (I am in the front row) on a trip from Leningrad to Kiev. We wanted to make sure that we’d spend May 1st (Labor Day in the Soviet Union) in Kiev! We took that picture in Gomel, which is about 80 miles away from Chernobyl, where our train made a regular stop. We were instructed to bury some pieces of clothing and shoes after coming back to Leningrad due to excess of radioactive dust on them…
“Ladies and gentlemen, we have detected gravitational waves.” February 11, 2016Posted by apetrov in Uncategorized.
The title says it all. Today, The Light Interferometer Gravitational-Wave Observatory (or simply LIGO) collaboration announced the detection of gravitational waves coming from the merger of two black holes located somewhere in the Southern sky, in the direction of the Magellanic Clouds. In the presentation, organized by the National Science Foundation, David Reitze (Caltech), Gabriela Gonzales (Louisiana State), Rainer Weiss (MIT), and Kip Thorn (Caltech), announced to the room full of reporters — and thousand of scientists worldwide via the video feeds — that they have seen a gravitational wave event. Their paper, along with a nice explanation of the result, can be seen here.
The data that they have is rather remarkable. The event, which occurred on 14 September 2015, has been seen by two sites (Livingston and Hanford) of the experiment, as can be seen in the picture taken from their presentation. It likely happened over a billion years ago (1.3B light years away) and is consistent with the merger of two black holes, of 29 and 46 solar masses. The resulting larger black hole’s mass is about 62 solar masses, which means that about 3 solar masses of energy (29+36-62=3) has been radiated in the form of gravitational waves. This is a huge amount of energy! The shape of the signal is exactly what one should expect from the merging of two black holes, with 5.1 sigma significance.
It is interesting to note that the information presented today totally confirms the rumors that have been floating around for a couple of months. Physicists like to spread rumors, as it seems.
Since the gravitational waves are quadrupole, the most straightforward way to see the gravitational waves is to measure the relative stretches of the its two arms (see another picture from the MIT LIGO site) that are perpendicular to each other. Gravitational wave from black holes falling onto each other and then merging. The LIGO device is a marble of engineering — one needs to detect a signal that is very small — approximately of the size of the nucleus on the length scale of the experiment. This is done with the help of interferometry, where the laser beams bounce through the arms of the experiment and then are compared to each other. The small change of phase of the beams can be related to the change of the relative distance traveled by each beam. This difference is induced by the passing gravitational wave, which contracts one of the arms and extends the other. The way noise that can mimic gravitational wave signal is eliminated should be a subject of another blog post.
This is really a remarkable result, even though it was widely expected since the (indirect) discovery of Hulse and Taylor of binary pulsar in 1974! It seems that now we have another way to study the Universe.
Nobel Prize in Physics 2015 October 6, 2015Posted by apetrov in Uncategorized.
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So, the Nobel Prize in Physics 2015 has been announced. To much surprise of many (including the author), it was awarded jointly to Takaaki Kajita and Arthur B. McDonald “for the discovery of neutrino oscillations, which shows that neutrinos have mass.” Well deserved Nobel Prize for a fantastic discovery.
What is this Nobel prize all about? Some years ago (circa 1997) there were a couple of “deficit” problems in physics. First, it appeared that the detected number of (electron) neutrinos coming form the Sun was measured to be less than expected. This could be explained in a number of ways. First, neutrino could oscillate — that is, neutrinos produced as electron neutrinos in nuclear reactions in the Sun could turn into muon or tau neutrinos and thus not be detected by existing experiments, which were sensitive to electron neutrinos. This was the most exciting possibility that ultimately turned out to be correct! But it was by far not the only one! For example, one could say that the Standard Solar Model (SSM) predicted the fluxes wrong — after all, the flux of solar neutrinos is proportional to core temperature to a very high power (~T25 for 8B neutrinos, for example). So it is reasonable to say that neutrino flux is not so well known because the temperature is not well measured (this might be disputed by solar physicists). Or something more exotic could happen — like the fact that neutrinos could have large magnetic moment and thus change its helicity while propagating in the Sun to turn into a right-handed neutrino that is sterile.
The solution to this is rather ingenious — measure neutrino flux in two ways — sensitive to neutrino flavor (using “charged current (CC) interactions”) and insensitive to neutrino flavor (using “neutral current (NC) interactions”)! Choosing heavy water — which contains deuterium — is then ideal for this detection. This is exactly what SNO collaboration, led by A. McDonald did
As it turned out, the NC flux was exactly what SSM predicted, while the CC flux was smaller. Hence the conclusion that electron neutrinos would oscillate into other types of neutrinos!
Another “deficit problem” was associated with the ratio of “atmospheric” muon and electron neutrinos. Cosmic rays hit Earth’s atmosphere and create pions that subsequently decay into muons and muon neutrinos. Muons would also eventually decay, mainly into an electron, muon (anti)neutrino and an electron neutrino, as
As can be seen from the above figure, one would expect to have 2 muon-flavored neutrinos per one electron-flavored one.
This is not what Super K experiment (T. Kajita) saw — the ratio really changed with angle — that is, the ratio of neutrino fluxes from above would differ substantially from the ratio from below (this would describe neutrinos that went through the Earth and then got into the detector). The solution was again neutrino oscillations – this time, muon neutrinos oscillated into the tau ones.
The presence of neutrino oscillations imply that they have (tiny) masses — something that is not predicted by minimal Standard Model. So one can say that this is the first indication of physics beyond the Standard Model. And this is very exciting.
I think it is interesting to note that this Nobel prize might help the situation with funding of US particle physics research (if anything can help…). It shows that physics has not ended with the discovery of the Higgs boson — and Fermilab might be on the right track to uncover other secrets of the Universe.
Nobel week 2015 October 5, 2015Posted by apetrov in Blogroll, Physics, Science.
Tags: physics, precision measurements
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So, once again, the Nobel week is upon us. And one of the topics of conversations for the “water cooler chat” in physics departments around the world is speculations on who (besides the infamous Hungarian “physicist” — sorry for the insider joke, I can elaborate on that if asked) would get the Nobel Prize in physics this year. What is your prediction?
With invention of various metrics for “measuring scientific performance” one can make educated guesses — and even put predictions on the industrial footage — see Thomson Reuters predictions based on a number of citations (they did get the Englert-Higgs prize right, but are almost always off). Or even try your luck with on-line betting (sorry, no link here — I don’t encourage this). So there is a variety of ways to make you interested.
Harvard University is to change its name April 1, 2015Posted by apetrov in Uncategorized.
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A phrase from William Shakespeare’s Romeo and Juliet states: “What’s in a name? That which we call a rose By any other name would smell as sweet.” This cannot be any further from the truth in the corporate world. The name of a corporation is its face, so setting a brand requires a lot of work and money. But what happens when something goes wrong? The way to deal with corporate problems often involves re-branding, changing the name and the face of the corporation. It works as customers usually do not check the history of a company before buying its products or using its services. It simply works.
With the Universities today run according to the corporate model, it was only a matter of time until re-branding came to the academic world. And leading Universities, like Harvard, seem to be embracing the model. Since 2013 article in Harvard Crimson, big Universities became a focus of investigations of many leading newspapers and politicians. Harvard, in particular, has been a focus of a brewing controversy. The University with the largest endowment of any university in the world, has got its name associated with the person who was not, in fact, the founder of Harvard University. As reported, in the very recent internal investigation by Harvard Crimson, John Harvard cannot be the founder of the school, because the Massachusetts Colony’s vote had come two years prior to Harvard’s bequest (compare this to Ezra Cornell’s founding of Cornell University). This led several prominent Massachusetts politicians to suggest that the University will be returned to the ownership by the Commonwealth with its name changed to University of Massachusetts, Cambridge. “We have a fantastic University system here in Massachusetts, with the flagship campus in Amherst,” said one of the prominent politicians who preferred not to be named, “Any University in the World would be proud to be a part of it.”
Returning a prominent private University to the ownership by the State is highly unusual nowadays and is probably highly specific to New England. With tightening budgets many states seek to privatize the Universities to remove them from their budget. For instance, there is a talk that a large public Midwestern school, Wayne State University, will soon change its owners and its name. Two prominent figures, W. Rooney and W. Gretzky, are rumored to work on acquiring the University and re-branding it as simply Wayne’s University. And the changes are rumored go even further. An external company Haleburton has already completed an assessment of the University’s strengths. The company noted WSU’s worldwide reputation in chemistry, physics and medicine and its Carnegie I research status, and recommended that the school should concentrate its efforts on graduating hockey, football, basketball and baseball players. “We are preparing our graduates to have highly successful careers. What job in the United States brings more money than the NFL or NHL player?” a member of WSU’s Academic Senate has been quoted in saying. “We are all excited about the change and looking forward to what else future would bring us.”
So, you want to go on sabbatical… February 5, 2015Posted by apetrov in Blogroll, Near Physics, Physics, Science.
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Every seven years or so a professor in a US/Canadian University can apply for a sabbatical leave. It’s a very nice thing: your University allows you to catch up on your research, learn new techniques, write a book, etc. That is to say, you become a postdoc again. And in many cases questions arise: should I stay at my University or go somewhere else? In many cases yearlong sabbaticals are not funded by the home University, i.e. you have to find additional sources of funding to keep your salary.
I am on a year-long sabbatical this academic year. So I had to find a way to fund my sabbatical (my University only pays 60% of my salary). I spent Fall 2014 semester at Fermilab and am spending Winter 2015 semester at the University of Michigan, Ann Arbor.
Here are some helpful resources for those who are looking to fund their sabbatical next year. As you could see from the list, they are slightly tilted towards theoretical physics. Yet, there are many resources that are useful for any profession. Of course your success depends on many factors: whether or not you would like to stay in the US or go abroad, competition, etc.
- General resources:
Fulbright Scholar Program
IAS Princeton (Member/Sabbatical)
Radcliffe Institute at Harvard University
Marie Curie International Incoming Fellowships
CERN Short Term visitors
I don’t pretend to have a complete list, but those sites were useful for me. I did not apply to all of those programs — and rather unfortunately, missed a deadline for the Simons Fellowship. Many University also have separate funds for sabbatical visitors. So if there is a University one wants to visit, it’s best to ask.
On a final note, it might be useful to be prepared and figure out, if you get funded, how the money/fellowship will find a way to your University and to you. Also, in many cases “60% of the salary” paid by your University while you are on a sabbatical leave means that you would have to find not only the remaining 40% of your salary, but also fringes that your University would take from your fellowship. So the amount that you’d need to find is more than 40% of your salary. Please don’t make a mistake that I made.
Data recall at the LHC? April 1, 2014Posted by apetrov in Uncategorized.
Tags: check the date, particle physics, physics
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In a stunning turn of events, Large Hadron Collider (LHC) management announced a recall and review of thousands of results that came from its four main detectors, ATLAS, CMS, LHCb and ALICE, in the course of the past several years when it learned that the ignition switches used to start the LHC accelerator (see the image) might have been produced by GM.
GM’s CEO, A. Ibarra, who is better known in the scientific world for the famous Davidson-Ibarra bound in leptogenesis, will be testifying on the Capitol Hill today. This new revelation will definitely add new questions to already long list of queries to be addressed by the embattled CEO. In particular, the infamous LHC disaster that happened on 10 September 2008, which cost taxpayers over 21Million dollars to fix, and has long suspected been caused by a magnet quench, might have been caused by too much paper accidentally placed on a switch by a graduate student, who was on duty that day.
“We want to know why it took LHC management five years to issue that recall”, an unidentified US Government official said in the interview, “We want to know what is being done to correct the problem. From our side, we do everything humanly possible to accommodate US high energy particle physics researchers and help them to avoid such problems in the future. For example, we included a 6.6% cut in US HEP funding in the President’s 2015 budget request.” He added, “We suspected that something might be going on at the LHC after it was convincingly proven to us at our weekly seminar that the detected Higgs boson is ‘simply one Xenon atom of the 1 trillion 167 billion 20 million Xenon atoms which there are in the LHC!’”
This is not the first time accelerators cause physicists to rethink their results and designs. For example, last year Japanese scientists had to overcome the problem of unintended acceleration of positrons at their flagship facility KEK.
At this point, it is not clear how GM’s ignition switches problems would affect funding of operations at the National Ignition Facility in Livermore, CA.
And the 2013 Nobel Prize in Physics goes to… October 8, 2013Posted by apetrov in Particle Physics, Physics, Science, Uncategorized.
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Today the 2013 Nobel Prize in Physics was awarded to François Englert (Université Libre de Bruxelles, Belgium) and Peter W. Higgs (University of Edinburgh, UK). The official citation is “for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN’s Large Hadron Collider.” What did they do almost 50 years ago that warranted their Nobel Prize today? Let’s see (for the simple analogy see my previous post from yesterday).
The overriding principle of building a theory of elementary particle interactions is symmetry. A theory must be invariant under a set of space-time symmetries (such as rotations, boosts), as well as under a set of “internal” symmetries, the ones that are specified by the model builder. This set of symmetries restrict how particles interact and also puts constraints on the properties of those particles. In particular, the symmetries of the Standard Model of particle physics require that W and Z bosons (particles that mediate weak interactions) must be massless. Since we know they must be massive, a new mechanism that generates those masses (i.e. breaks the symmetry) must be put in place. Note that a theory with massive W’s and Z that are “put in theory by hand” is not consistent (renormalizable).
The appropriate mechanism was known in the beginning of the 1960’s. It goes under the name of spontaneous symmetry breaking. In one variant it involves a spin-zero field whose self-interactions are governed by a “Mexican hat”-shaped potential
It is postulated that the theory ends up in vacuum state that “breaks” the original symmetries of the model (like the valley in the picture above). One problem with this idea was that a theorem by G. Goldstone required a presence of a massless spin-zero particle, which was not experimentally observed. It was Robert Brout, François Englert, Peter Higgs, and somewhat later (but independently), by Gerry Guralnik, C. R. Hagen, Tom Kibble who showed a loophole in a version of Goldstone theorem when it is applied to relativistic gauge theories. In the proposed mechanism massless spin-zero particle does not show up, but gets “eaten” by the massless vector bosons giving them a mass. Precisely as needed for the electroweak bosons W and Z to get their masses! A massive particle, the Higgs boson, is a consequence of this (BEH or Englert-Brout-Higgs-Guralnik-Hagen-Kibble) mechanism and represents excitation of the Higgs field about its new vacuum state.
It took about 50 years to experimentally confirm the idea by finding the Higgs boson! Tracking the historic timeline, the first paper by Englert and Brout, was sent to Physical Review Letter on 26 June 1964 and published in the issue dated 31 August 1964. Higgs’ paper, received by Physical Review Letters on 31 August 1964 (on the same day Englert and Brout’s paper was published) and published in the issue dated 19 October 1964. What is interesting is that the original version of the paper by Higgs, submitted to the journal Physics Letters, was rejected (on the grounds that it did not warrant rapid publication). Higgs revised the paper and resubmitted it to Physical Review Letters, where it was published after another revision in which he actually pointed out the possibility of the spin-zero particle — the one that now carries his name. CERN’s announcement of Higgs boson discovery came 4 July 2012.
Is this the last Nobel Prize for particle physics? I think not. There are still many unanswered questions — and the answers would warrant Nobel Prizes. Theory of strong interactions (which ARE responsible for masses of all luminous matter in the Universe) is not yet solved analytically, the nature of dark matter is not known, the picture of how the Universe came to have baryon asymmetry is not cleared. Is there new physics beyond what we already know? And if yes, what is it? These are very interesting questions that need answers.
Higgs mechanism for electrical engineers October 7, 2013Posted by apetrov in Particle Physics, Physics, Science, Uncategorized.
Tags: higgs boson
Since the Higgs boson’s discovery a little over a year ago at CERN I have been getting a lot of questions from my friends to explain to them “what this Higgs thing does.” So I often tried to use the crowd analogy that is ascribed to Prof. David Miller, to describe the Higgs (or Englert-Brout-Higgs-Guralnik-Hagen-Kibble) mechanism. Interestingly enough, it did not work well for most of my old school friends, majority of whom happen to pursue careers in engineering. So I thought that perhaps another analogy would be more appropriate. Here it is, please let me know what you think!
Imagine Higgs field as represented by some quantity of slightly magnetized iron filings, i.e. small pieces of iron that look like powder, spread over a table or other surface to represent Higgs field that permeates the Universe. Iron filings are common not only as dirt in metal shops, they are often used in school experiments and other science demonstrations to visualize the magnetic field. It is important for them to be slightly magnetized, as this represents self-interaction of the Higgs field. Here they are pictured in a somewhat cartoonish way:
How can Higgs field generate mass? Moreover, how can one field generate different masses for different types of particles? Let us first make an analogue of fermion mass generation. If we take a small magnet and put it in the filings, the magnet would pick up a bunch of filings, right? How much would it pick up? It depends on the “strength” of that magnet. It could be a little:
…or it could be a lot, depending on what kind of magnet we use — or how strong it is:
If we neglect the masses of our magnets, as we assumed they are small, the mass of the picked up mess with the magnets inside is totally determined by the mass of the picked filings, which in turn is determined by the interaction strength between the magnets and the filings. This is precisely how fermion mass generation works in the Standard Model!
In the Standard Model the massless fermions are coupled to the Higgs field via so-called Yukawa interactions, whose strength is parametrized by a number, the Yukawa coupling constant. For different fermion types (or flavors) the couplings would be numerically different, ranging from one to one part in a million. As a result of interaction with the Higgs field (NOT the boson!) in the form of its vacuum expectation value, all fermions acquire masses (ok, maybe not all — neutrinos could be different). And those masses would depend on the strength of the interaction of fermions with Higgs field, just like in our example with magnets and iron filings!
Now imagine that we simply kicked the table! No magnets. The filings would clamp together to form lumps of filings. Each lump would have a mass, which would only depend on how strong the filings attract to each other (remember that they are slightly magnetized?). If we don’t know how strong they are magnetized, we cannot tell how massive each lamp will be, so we would have to measure their masses.
This gives a good analogy of the fact that Higgs boson is an excitation of the Higgs field (the fact that was pointed out by Higgs), and why we cannot predict its mass from the first principles, but need a direct observation at the LHC!
Notice that this picture (so far) does not provide direct analogy to how gauge bosons (W’s and Z bosons) receive their masses. W’s and Z are also initially massless because of the gauge (internal) symmetries required by the construction of the Standard Model. We did know their mass from earlier CERN and SLAC experiments — and even prior to those, we knew that W’s were massive from the fact that weak interactions are of the finite range.
To extend our analogy, let’s clean up the mess — literally! Let’s throw a bucket of water over the table covered with those iron filings and see what happens. Streams of water would pick up iron filings and flow from the table. Assuming that that water’s mass is negligible, the total mass of those water streams (aka dirty water) would be completely determined by the mass of picked iron filings, just like masses of W’s and Z are determined by the Higgs field.
This explanation seemed to work better for my engineering friends! What do you think?
Digital bureaucracy August 9, 2013Posted by apetrov in Near Physics.
This post is about how digital technology of the 21st century “helps” professors (well, at least, this professor) to spend his time doing very important paper submission. Except for the fact that “paper” here refers to the receipts of the expenses that were incurred attending professional conferences. Sorry in advance for the rant that follows.
As an introduction, let me tell you how the procedure used to work at our University. Before going to a conference I had to “encumber” (“reserve”) expenses that I planed to incur – filling out one paper form, no receipts. After return from the conference, I would fill out the same form and attach receipts. Our secretary would then type the form up nicely and submit it for reimbursement. It would normally take weeks to get reimbursed, but timewise I’d spend only about 10-15 min doing the whole procedure. Including a nice cover letter to the said secretary summarizing the details and thanking her for her job. 15 min.
Enter digital age! And the age of layoffs. With great fanfare, the university rolled out a new digital system in 2012 — no paper (save the trees!), no secretary involvement (remember the age of layoffs?), maybe even quick turn-around, yahoo!!! Even MIT does not have such a system! Take that, MIT!
Except for now I have to first file the request, complete with all receipts and a conference agenda. No problem, right? So it takes about 20 min to collect all receipts, turn them into pdf files and fill out a bunch of forms electronically. Now, upon return you do the same thing. Except for now you have to
– digitize the receipts that were not digital originally (like highway tolls or gas),enter those receipts separately based on the day when the charge occurred,
– provide proof that you paid for your hotels with your own credit card — not the university one (no problem of getting the pdf file from your credit card company, blacking out your personal details and submitting, attaching it electronically to the request). Also, you’d need to itemize your hotel stay — enter how much it was per day + taxes, etc.
– you have to once again attach the same files with conference agenda.
And, of course, you have to state the business purpose of all of your lunches and dinners (not to die of hunger during the conference, I suppose?) separately for each day of the conference.
Of course, all of this is not a problem. It only takes 30-40 min to do all of this. If you know how. So, if my math is correct (and your expense report is not returned back — so you have to fix your problems and resubmit), the whole procedure takes about 20 min+40 min = 1 hour (60 min – remember 15 min???). Moreover, no secretary involvement, remember? I do it all myself, so the said secretary is fired.
So here is some interesting math. it takes, on average, 4 times longer for me to file the digital reports. I know now why MIT does not have such a system. I’ll take that back, MIT…. Questions remain, though. Do faculty have to do all of those reports on their own time or during the time when they are supposed to do research or write grant applications or talk to students? Does the university save money on that (hint: secretary’s salary is on average less than that of a faculty)?
So here you have it. Does it kill me to do all those things? Of course not. As it wouldn’t kill me to mop the floor in the corridor near my office or go to a supply store to buy chalk to teach my class. Hey, here is an idea for new cost-cutting measures!