Author Archives: Clifford

News from the Front, XVIII: de Sitter Black Holes and Continuous Heat Engines

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[caption id="attachment_19313" align="alignright" width="250"] Hubble photo of jupiter’s aurorae.[/caption]Another title for this could be “Making sense of de Sitter black hole thermodynamics”, I suppose. What I’m going to tell you about is either a direct correspondence or a series of remarkable inspiring coincidences. Either way, I think you will come away agreeing that there is certainly something interesting afoot.

It is an idea I’d been tossing around in my head from time to time over years, but somehow did not put it all together, and then something else I was working on years later, that was seemingly irrelevant, helped me complete the puzzle, resulting in my new paper, which (you guessed it) I’m excited about.

It all began when I was thinking about heat engines, for black holes in anti-de Sitter, which you may recall me talking about in posts here, here, and here, for example. Those are reciprocating heat engines, taking the system through a cycle that -through various stages- takes in heat, does work, and exhausts some heat, then repeats and repeats. And repeats.

I’ve told you the story about my realisation that there’s this whole literature on quantum heat engines that I’d not known about, that I did not even know of a thing called a quantum heat engine, and my wondering whether my black hole heat engines could have a regime where they could be considered quantum heat engines, maybe enabling them to be useful tools in that arena…(resulting in the paper I described here)… and my delight in combining 18th Century physics with 21st Century physics in this interesting way.

All that began back in 2017. One thing I kept coming back to that really struck me as lovely is what can be regarded as the prototype quantum heat engine. It was recognized as such as far back as 1959!! It is a continuous heat engine, meaning that it does its heat intake and work and heat output all at the same time, as a continuous flow. It is, in fact a familiar system – the three-level maser! (a basic laser also uses the key elements).

A maser can be described as taking in energy as heat from an external source, and giving out energy in the form of heat and work. The work is the desired […] Click to continue reading this post →

News from the Front, XVII: Super-Entropic Instability

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I’m quite excited because of some new results I got recently, which appeared on the ArXiv today. I’ve found a new (and I think, possibly important) instability in quantum gravity.

Said more carefully, I’ve found a sibling to Hawking’s celebrated instability that manifests itself as black hole evaporation. This new instability also results in evaporation, driven by Hawking radiation, and it can appear for black holes that might not seem unstable to evaporation in ordinary circumstances (i.e., there’s no Hawking channel to decay), but turn out to be unstable upon closer examination, in a larger context. That context is the extended gravitational thermodynamics you’ve read me talking about here in several previous posts (see e.g. here and here). In that framework, the cosmological constant is dynamical and enters the thermodynamics as a pressure variable, p. It has a conjugate, V, which is a quantity that can be derived once you know the pressure and the mass of the black hole.

Well, Hawking evaporation is a catastrophic quantum phenomenon that follows from the fact that the radiation temperature of a Schwarzschild black hole (the simplest one you can think of) goes inversely with the mass. So the black hole radiates and loses energy, reducing its mass. But that means that it will radiate at even higher temperature, driving its mass down even more. So it will radiate even more, and so on. So it is an instability in the sense that the system drives itself even further away from where it started at every moment. Like a pencil falling over from balancing on a point.

This is the original quantum instability for gravitational systems. It’s, as you probably know, very important. (Although in our universe, the temperature of radiation is so tiny for astrophysical black holes (they have large mass) that the effect is washed out by the local temperature of the universe… But if the univverse ever had microscopic black holes, they’d have radiated in this way…)

So very nice, so very 1970s. What have I found recently?

A nice way of expressing the above instability is to simply say […] Click to continue reading this post →

News from the Front, XVI: Toward Quantum Heat Engines

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(The following post is a bit more technical than usual. But non-experts may still find parts helpful.)

A couple of years ago I stumbled on an entire field that I had not encountered before: the study of Quantum Heat Engines. This sounds like an odd juxtaposition of terms since, as I say in the intro to my recent paper:

The thermodynamics of heat engines, refrigerators, and heat pumps is often thought to be firmly the domain of large classical systems, or put more carefully, systems that have a very large number of degrees of freedom such that thermal effects dominate over quantum effects. Nevertheless, there is thriving field devoted to the study—both experimental and theoretical—of the thermodynamics of machines that use small quantum systems as the working substance.

It is a fascinating field, with a lot of activity going on that connects to fields like quantum information, device physics, open quantum systems, condensed matter, etc.

Anyway, I stumbled on it because, as you may know, I’ve been thinking (in my 21st-meets-18th century way) about heat engines a lot over the last five years since I showed how to make them from (quantum) black holes, when embedded in extended gravitational thermodynamics. I’ve written it all down in blog posts before, so go look if interested (here and here).

In particular, it was when working on a project I wrote about here that I stumbled on quantum heat engines, and got thinking about their power and efficiency. It was while working on that project that I had a very happy thought: Could I show that holographic heat engines (the kind I make using black holes) -at least a class of them- are actually, in some regime, quantum heat engines? That would be potentially super-useful and, of course, super-fun.

The blunt headline statement is that they are, obviously, because every stage […] Click to continue reading this post →

Endgame Memories

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About 2-3 (ish) years ago, I was asked to visit the Disney/Marvel mothership in Burbank for a meeting. I was ushered into the inner workings of the MCU, past a statue of the newly acquired Spidey, and into a room. Present were Christopher Markus and Stephen McFeely, the writers of … Click to continue reading this post →

Event!

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Well, I’m off to get six hours of sleep before the big announcement tomorrow! The Event Horizon Telescope teams are talking about an announcement of “groundbreaking” results tomorrow at 13:00 CEST. Given that they set out to “image” the event horizon of a black hole, this suggests (suggests) that they … Click to continue reading this post →

Painted

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You may have heard that there are an estimated 1 billion Painted Lady butterflies passing through the Los Angeles area right now. Just after sunrise this morning I watched them begin their daily swarming. Fascinating! Later, just after lunch, I captured some quick shots of this one for you… -cvj

Available Now!

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Oh, that talk I did at Perimeter? It is available online now. It is all about the process of making the book “The Dialogues”, why I did it and how I did it. Along the way, I show some examples and talk about the science they’re bringing to life, but this is not primarily a science talk but a talk about talking about science, if you see what I mean.

The talk starts slowly, but bear with me and it warms up swiftly!

YouTube link here. Ended below:
[…] Click to continue reading this post →

Black Holes and Time Travel in your Everyday Life

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Oh, look what I found! It is my talk “Black Holes and Time Travel in your Everyday Life”, which I gave as the Klopsteg Award lecture at AAPT back in July. Someone put it on YouTube. I hope you enjoy it!

Two warnings: (1) Skip to about 6 minutes to start, to avoid all the embarrassing handshaking and awarding and stuff. (2) There’s a bit of early morning slowness + jet lag in my delivery here and there, so sorry about that. 🙂

Embed:

Abstract: […] Click to continue reading this post →

Black Market of Ideas

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As a reminder, today I’ll be at the natural history museum (LA) as part of the “Night of Ideas” event! I’ll have a number of physics demos with me and will be at a booth/table (in the Black Market of Ideas section) talking about physics ideas underlying our energy future as a species. I’ll sign some books too! Come along!

Here’s link to the event: https://nhm.org/site/activities-programs/night-of-ideas

-cvj
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An Update!

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Well, hello to you and to 2019!

It has been a little while since I wrote here and not since last month when it was also last year, so let’s break that stretch. It was not a stretch of entire quiet, as those of you who follow on social media know (twitter, instagram, Facebook… see the sidebar for links), but I do know some of you don’t directly on social media, so I apologise for the neglect.

The fact is that I’ve been rather swamped with several things, including various duties that were time consuming. Many of them I can’t talk about, since they are not for public consumption (this ranges from being a science advisor on various things – some of which will be coming at you later in the year, to research projects that I’d rather not talk about yet, to sitting on various committees doing the service work that most academics do that helps the whole enterprise keep afloat). The most time-consuming of the ones I can talk about is probably being on the search committee for an astrophysics job for which we have an opening here at USC. This is exciting since it means that we’ll have a new colleague soon, doing exciting things in one of a variety of exciting areas in astrophysics. Which area still is to be determined, since we’ve to finish the search yet. But it did involve reading through a very large number of applications (CVs, cover letters, statements of research plans, teaching philosophies, letters of recommendation, etc), and meeting several times with colleagues to narrow things down to a (remarkable) short list… then hosting visitors/interviewees, arrangement meetings, and so forth. It is rather draining, while at the same time being very exciting since it marks a new beginning! It has been a while since we hired in this area in the department, and there’s optimism that this marks a beginning of a re-invigoration for certain research areas here.

Physics research projects have been on my mind a lot, of course. I remain very excited abut the results that I reported on in a post back in June, and I’ve been working on new ways of building on them. (Actually, I did already do a followup paper that I did not write about here. For those who are interested, it is a whole new way of defining a new generalisation of something called the Rényi entropy, that may be of interest to people in many fields, from quantum information to string theory. I ought to do a post, since it is a rather nice construction that could be useful in ways I’ve not thought of!) I’ve been doing some new explorations of how to exploit the central results in useful ways: Finding a direct link between the Second Law of Thermodynamics and properties of RG flow in quantum field theory ought to have several consequences beyond the key one I spelled out in the paper with Rosso (that Zamolodchikov’s C-theorem follows). Im particular, I want to sharpen it even further in terms of something following from heat engine constraints, as I’ve been aiming to do for a while. (See the post for links to earlier posts about the ‘holographic heat engines” and their role.)

You might be wondering how the garden is doing, since that’s something I post about here from time to time. Well, right now there is an on-going deluge of rain (third day in a row) that is a pleasure to see. The photo at the top of the page is one I took a few days ago when the sky was threatening the downpours we’re seeing now. The rain and the low temperatures for a while will certainly help to renew and refresh things out there for the (early) Spring planting I’ll do soon. There’ll be fewer bugs and bug eggs that will […] Click to continue reading this post →