I put a set of new results out on to the arxiv recently. They were fun to work out. They represent some of my continued fascination with holographic heat engines, those things I came up with back in 2014 that I think I’ve written about here before (here and here). For various reasons (that I’ve explained in various papers) I like to think of them as an answer waiting for the right question, and I’ve been refining my understanding of them in various projects, trying to get clues to what the question or questions might be.
As I’ve said elsewhere, I seem to have got into the habit of using 21st Century techniques to tackle problems of a 19th Century flavour! The title of the paper is “Approaching the Carnot limit at finite power: An exact solution”. As you may know, the Carnot engine, whose efficiency is the best a heat engine can do (for specified temperatures of exchange with the hot and cold reservoirs), is itself not a useful practical engine. It is a perfectly reversible engine and as such takes infinite time to run a cycle. A zero power engine is not much practical use. So you might wonder how close a real engine can come to the Carnot efficiency… the answer should be that it can come arbitrarily close, but most engines don’t, and so people who care about this sort of thing spend a lot of time thinking about how to design special engines that can come close. And there are various arguments you can make for how to do it in various special systems and so forth. It’s all very interesting and there’s been some important work done.
What I realized recently is that my old friends the holographic heat engines are a very good tool for tackling this problem. Part of the reason is that the underlying working substance that I’ve been using is a black hole (or, if you prefer, is defined by a black hole), and such things are often captured as exact […] Click to continue reading this post
Wow! Topology in the mainstream news. I never thought I’d see the day. Congratulations to the winners! Citation:
The Nobel Prize in Physics 2016 was divided, one half awarded to David J. Thouless, the other half jointly to F. Duncan M. Haldane and J. Michael Kosterlitz “for theoretical discoveries of topological phase transitions and topological phases of matter”.
Here is a link to the Nobel Prize site with more information, and also, here’s a BBC breakdown of some of the science.
An important (to some) side note: Duncan Haldane was at USC when he wrote the cited papers. Great that USC was supportive of this kind of work, especially in that early part of his career.
-cvj Click to continue reading this post
Sorry I’ve been quiet for a long stretch recently. I’ve been tied up with travel, physics research, numerous meetings of various sorts (from the standard bean-counting variety to the “here’s three awesome science-y things to put into your movie/TVshow” variety*), and other things, like helping my garden survive this heatwave.
I’ve lost some time on the book, but I’m back on it for a while, and have […] Click to continue reading this post
For the first time in its history, the Southern California Strings Seminar was held in Santa Barbara, at the KITP! It was probably the largest meeting that has been held under that banner, with attendance from all over the map of theory groups in the region. Thanks for Edgar Shaghoulian for organising it!
Although I was a bit under the weather (never really figured out what the matter was) and super-pressed for time, I went along to support it and learn a bit about what was going on. I think that there’ll be a posting on the KITP’s online talks website at some point with the various talks, so you can look in too (keep an eye on their website).
I did not fancy driving there and playing dodgems with the traffic and so -as seems to be my custom when [….] Click to continue reading this post
This month’s issue of Physics Today has a review that I wrote of the book “Quantum Field Theory for the Gifted Amateur”, by Tom Lancaster and Stephen J. Blundell. I took the opportunity to give a broader view (albeit brief, given the word limit) of the landscape of books on that subject and how it has changed a lot, in a way that I think reflects some excellent changes in formal theory brought about by (at least in part) research into the many topics pulled together under the broad umbrella of string theory. As you might know from reading here and elsewhere, I’ve long been pushing for the increased application of the ideas and techniques of string theory to other areas of physics, and it has become quite the thing these days, I’m happy to see. Such research has resulted in the blurring of the […] Click to continue reading this post
Apparently I was on an episode of the BBC program Horizon a couple of hours ago over in the UK. I completely forgot that was coming up and forgot to mention it. Sorry! I’ve no idea what parts of the interview with me they used, or what the final thrust of the episode is, but I did have a lot of fun shooting the episode with the filmmakers over in Joshua Tree some time last year. See a post I did about it here. I spent some time explaining why negative mass is problematic, especially in the context of gravity… The program talks a lot about people who are trying to find anti-gravity of various sorts. I was reminded that the episode aired since I found myself tagged on social media, and wondered what the ruckus was about. Then I found the following tweet by @homeworkjunkie with a screen shot, and the caption “Nice reaction to runaway problem;zero cost energy proposed by some people in BBC Horizon”:
[…] Click to continue reading this post
Well, 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.
*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
Ok, 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
These stairs probably do not conform to any building code, but I like them anyway, and so they will appear in a paper I’ll submit to the arxiv soon.
They’re part of a nifty algorithm I thought of on Friday that I like rather a lot.
-cvj Click to continue reading this post
Today’s big conundrum: Call this curve a knee or an elbow?
On the one hand, it goes from horizontal to vertical, so obviously a knee.
On the other hand, the little bump before the plunge is sort of a bit like a cartoon elbow*. Think of Popeye, etc.
*Or perhaps a real one, but with a case of olecranon bursitis… Click to continue reading this post
My friends over at UCLA took the reins for the regional meeting known as the Southern California Strings Seminar this semester, and the shot above (a tad blurry) is from the event, which was today. We had four excellent talks (I […] Click to continue reading this post
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
So here I am at the boarding gate at LAX, ready for my flight. I’m off to Mexico City. What’s on my mind? :- What will I be doing on the plane? What am I in the mood for? What I really should be doing, perhaps, is preparing the four … Click to continue reading this post
The 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
One 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