News from the Front, XIII: Holographic Heat Engines for Fun and Profit

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