Category Archives: research

Sabbatical Dreams Fulfilled!

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NYT_Simons_fellowship_announcement_2016Well, today’s hunt for a print copy of the New York Times (click for larger view) was easier than the Wall Street Journal hunt a couple of months back. Been a while since I was in the Science Times, and I’ve not been in it in this capacity before. The Simons Fellowship announcement was today, and I was awarded one. I’m honoured to be in such fine company! Nice to see my friends Lawrence Hall, Jeff Harvey, Petr Horava, Andy Strominger among my fellow Fellows, and congratulations to everyone!

This is a major part of my sabbatical planning for next academic year (half book-completing, half research), and it sure is great to get it. There aren’t many fellowships of this sort for my area of work. Thanks Simons Foundation and all concerned.

-cvj

*And when I say fulfilled… Well, there’s still the matter of actually doing the thing and getting all my planning to work out… Click to continue reading this post →

News from the Front, XIII: Simplicity

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adding_cyclesOk, I promised to explain the staircase I put up on Monday. I noticed something rather nice recently, and reported it (actually, two things) in a recent paper, here. It concerns those things I called “Holographic Heat Engines” which I introduced in a paper two years ago, and which I described in some detail in a previous post. You can go to that post in order to learn the details – there’s no point repeating it all again – but in short the context is an extension of gravitational thermodynamics where the cosmological constant is dynamical, therefore supplying a meaning to the pressure and the volume variables (p,V) that are normally missing in black hole thermodynamics… Once you have those, it seems obvious that you can start considering processes that do mechanical work (from the pdV term in the first law) and within a short while the idea of heat engines in which the black hole is the working substance comes along. Positive pressure corresponds to negative cosmological constant and so the term “holographic heat engines” is explained. (At least to those who know about holographic dualities.)

So you have a (p,V) plane, some heat flows, and an equation of state determined by the species of (asymptotically AdS) black hole you are working with. It’s like discovering a whole new family of fluids for which I know the equation of state (often exactly) and now I get to work out the properties of the heat engines I can define with them. That’s what this is.

Now, I suspect that this whole business is an answer waiting for a question. I can’t tell you what the question is. One place to look might be in the space of field theories that have such black holes as their holographic dual, but I’m the first to admit that […] Click to continue reading this post →

D-Brane Fun!

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image Turns out that it still a lot of fun to lecture about string theory and D-branes! (The latter are an important type of extended object, generalizing membranes, that have been very useful in theoretical physics for the last 20 years. — My goodness, it has been 20 years since Joe Polchinski first demonstrated their importance for string duality!) The students at the Latin American String School here in Mexico City seem to be very engaged and enjoying themselves. Although I was having fun I was also not without a presentation error or two brought on by […] Click to continue reading this post →

Thomas and Fermi

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thomas-fermiThe other day the Thomas-Fermi model (and its enhancements by Dirac and others) wandered across my desk (and one of my virtual blackboards as you can see in the picture) for a while. Putting aside why it showed up (perhaps I will say later on, but I cannot now), it was fun to delve for a while into some of these early attempts in quantum mechanics to try to understand approximation methods for treating fairly complicated quantum systems (like atoms of various sizes). The basic model showed up in 1927, just a year after Schrodinger’s […] Click to continue reading this post →

Goodbye Nambu

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nambu-gotoOne of the towering giants of the field, Yoichiro Nambu, passed away a short while ago, at age 94. He made a remarkably wide range of major (foundational) contributions to various fields, from condensed matter through particle physics, to string theory. His 2008 Nobel Prize was for work that was a gateway for other Nobel Prize-winning work, for example 2012’s Higgs particle work. He was an inspiration to us all. Here’s an excellent 1995 Scientific American piece (updated a bit in 2008) about him, which nicely characterises some of his style and contributions, with comments from several notable physicists. Here is a University of Chicago obituary, a Physics World one, one by Hirosi Ooguri, and one from the New York Times. There are several others worth reading too.

Since everyone is talking more about his wonderful work on symmetry-breaking (and rightly so), I’ve put up (on the board above) instead the Nambu-Goto action governing the motion of a relativistic string (written with a slight abuse of notation). This action, and its generalisations, is a cornerstone of string theory, and you’ll find it in pretty much every text on the subject. Enjoy.

Thank you, Professor Nambu.

-cvj Click to continue reading this post →

Earth Not Swallowed!

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So, here we are. Still in existence. Hurrah!

cern_LHC_tunnelThe Large Hadron Collider (image right is courtesy of CERN) started a new phase of experimental work today, colliding particles at double the energy it was working at a few years back when the Higgs was discovered. By time I was making breakfast and checking email, their live blog, etc., this morning, it was clear that (contrary to fears expressed by some) the LHC had not created a black hole that swallowed the earth, nor had it created some sort of strange chunk of new vacuum that condensed that of the entire universe into a new phase. (Or if it did either of those things, the effects are hardly noticeable!!)

As I keep emphasising (actually I’ll be talking about this to a puppet character on a TV show tomorrow too – details later) the LHC (or any of the particle collision experiments we’ve ever done) is not doing anything that Nature does not do routinely right here at earth (and most times way more violently and […] Click to continue reading this post →

‘t Hooft on Scale Invariance…

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Worth a read: This is ‘t Hooft’s summary (link is a pdf) of a very interesting idea/suggestion about scale invariance and its possible role in finding an answer to a number of puzzles in physics. (It is quite short, but think I’ll need to read it several times and mull over it a lot.) It won the top Gravity Research foundation essay prize this year, and there were several other interesting essays in the final list too. See here.

-cvj Click to continue reading this post →

Excellent Witten Interview!

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ooguri_witten_kavli_ipmuI just learned of an excellent interview with Edward Witten, one or our field’s grandmasters, or rather: the grandmasters’ grandmaster. I strongly recommend reading it. (This is for technically equipped people working in the field, most likely – I believe that it is not intended for the general public, although you are welcome to read it too!)

There’s a lot of discussion (of among other things like his current work) of that golden period during the 1990s that I had the privilege to work in during my postdoc years (some of them under the guidance of Witten) that remain one of […] Click to continue reading this post →

Sometimes there is Smoke without Fire

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…Or at least, not always the fire you’re looking for. So, as suspected for several months now, the signal seen by BICEP2 experiment and dubbed “a smoking gun” type of direct evidence for cosmic inflation (for which we have lots of strongly suggestive indirect evidence, by the way) is likely an artefact of the effects of galactic dust. I spoke about this in a post a while back, so I won’t repeat myself here. What everyone has been waiting for has been the results of a joint analysis between the BICEP2 people and the ESA’s Planck mission. The Planck satellite, you may recall from reading here or elsewhere, is also designed toPlanck_view_of_BICEP2_field_node_full_image_2 carefully study the polarisation of the cosmic microwave background (the earliest light to shine in the universe), and so can (through thorough analysis of the effects of dust that it has measured independently) help rule in or out whether there is a signal. Planck studies essentially the whole sky, not just the patch that BICEP2 was carefully looking at, and one of […] Click to continue reading this post →