It has been two weeks since it began, but I’m still pleased with the arrival of relatively chilly weather here in LA, because the heat, dust, grime, and smoke of the Summer and into the Fall (from fires, endless hot days, etc.,) was seemingly relentless, and really getting me down. … Click to continue reading this post
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Avengers cosplayers in the audience of my Friday panel.[/caption]It might surprise you to know just how much science gets into the mix at Comic-Con. This never makes it to the news of course – instead its all stories about people dressing up in costumes, and of course features about big movie and TV announcements. Somewhere inside this legendary pop culture maelstrom there’s something for nearly everyone, and that includes science. Which is as it should be. Here’s a look at two days I spent there. [I took some photos! (All except two here – You can click on any photo to enlarge it.]
Day 1 – Friday
I finalized my schedule rather late, and so wasn’t sure of my hotel needs until it was far too late to find two nights in a decent hotel within walking distance of the San Diego Convention Center — well, not for prices that would fit with a typical scientist’s budget. So, I’m staying in a motel that’s about 20 minutes away from the venue if I jump into a Lyft.
My first meeting is over brunch at the Broken Yolk at 10:30am, with my fellow panellists for the panel at noon, “Entertaining Science: The Real, Fake, and Sometimes Ridiculous Ways Science Is Used in Film and TV”. They are Donna J. Nelson, chemist and science advisor for the TV show Breaking Bad (she has a book about it), Rebecca Thompson, Physicist and author of a new book about the science of Game of Thrones, and our moderator Rick Loverd, the director of the Science and Entertainment Exchange, an organization set up by the National Academy of Sciences. I’m on the panel also as an author (I wrote and drew a non-fiction graphic novel about science called The Dialogues). My book isn’t connected to a TV show, but I’ve worked on many TV shows and movies as a science advisor, and so this rounds out the panel. All our books are from […] Click to continue reading this post
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Diamond maser. Image from Jonathan Breeze, Imperial College[/caption]This is part 2 of a chat about some recent thoughts and results I had about de Sitter black holes, reported in this arxiv preprint. Part 1 is here, so maybe best to read that first.
Now let us turn to de Sitter black holes. I mean here any black hole for which the asymptotic spacetime is de Sitter spacetime, which is to say it has positive cosmological constant. This is of course also interesting since one of the most natural (to some minds) possible explanations for the accelerating expansion of our universe is a cosmological constant, so maybe all black holes in our universe are de Sitter black holes in some sense. This is also interesting because you often read here about explorations of physics involving negative cosmological constant, so this is a big change!
One of the things people find puzzling about applying the standard black hole thermodynamics is that there are two places where the standard techniques tell you there should be a temperature associated with them. There’s the black hole horizon itself, and there’s also the cosmological horizon. These each have temperature, and they are not necessarily the same. For the Schwarzschild-de Sitter black hole, for example, (so, no spins or charges… just a mass with an horizon associated with it, like in flat space), the black hole’s temperature is always larger than that of the cosmological horizon. In fact, it runs from very large (where the black hole is small) all the way (as the black hole grows) to zero, where the two horizons coincide.
You might wonder, as many have, how to make sense of the two temperatures. This cannot, for a start, be an equilibrium thermodynamics system. Should there be dynamics where the two temperatures try to equalise? Is there heat flow from one horizon to another, perhaps? Maybe there’s some missing ingredient needed to make sense of this – do we have any right to be writing down temperatures (an equilibrium thermodynamics concept, really) when the system is not in equilibrium? (Actually, you could ask that about Schwarzschild in flat space – you compute the temperature and then discover that it depends upon the mass in such a way that the system wants to move to a different temperature. But I digress.)
The point of my recent work is that it is entirely within the realm of physics we have to hand to make sense of this. The simple system described in the previous post – the three level maser – has certain key interconnected features that seem relevant:
My point is that these features are all present for de Sitter black holes too, starting with the two temperatures. But you won’t see the rest by staring at just the Schwarzschild case, you need to add rotation, or charge (or both). As we shall see, the ability to reduce angular momentum, or to reduce charge, will be the work channel. I’ll come back to the maximum […] Click to continue reading this post
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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
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
(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
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
Yes, it’s a black hole all right. Following on from my reflections from last night, I can report that the press conference revelations were remarkable indeed. Above you see the image they revealed! It is the behemoth at the centre of the galaxy M87! This truly groundbreaking image is the … Click to continue reading this post
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
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. 🙂
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Abstract: […] Click to continue reading this post
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
And then two come along at once… Following on yesterday, another of the longer interviews I’ve done recently has appeared. This one was for Sean Carroll’s excellent Mindscape podcast. This interview/chat is all about string theory, including some of the core ideas, its history, what that “quantum gravity” thing is anyway, and why it isn’t actually a theory of (just) strings. Here’s a direct link to the audio, and here’s a link to the page about it on Sean’s blog.
The whole Mindscape podcast has had some fantastic conversations, by the way, so do check it out on iTunes or your favourite podcast supplier!
I hope you enjoy it!!
For your listening pleasure: I’ve been asked to do a number of longer interviews recently. One of these was for the “Futuristic Podcast of Mark Gerlach”, who interviews all sorts of people from the arts (normally) over to the sciences (well, he hopes to do more of that starting with me). Go and check out his show on iTunes. The particular episode with me can be found as episode 31. We talk about a lot of things, from how people get into science (including my take on the nature vs nurture discussion), through the changes in how people get information about science to the development of string theory, to black holes and quantum entanglement – and a host of things in between. We even talked about The Dialogues, you’ll be happy to hear. I hope you enjoy listening!
(The picture? Not immediately relevant, except for the fact that I did cycle to the place the recording took place. I mostly put it there because I was fixing my bike not long ago and it is good to have a photo in a post. That is all.)
I was asked by editors of the magazine Physics World’s 30th anniversary edition to do a drawing that somehow captures changes in physics over the last 30 years, and looks forward to 30 years from now. This was an interesting challenge. There was not anything like the freedom to use space that I had in other works I’ve done, like my graphic book about science “The Dialogues”, or my glimpse of the near future in my SF story “Resolution” in the Twelve Tomorrows anthology. I had over 230 pages for the former, and 20 pages for the latter. Here, I had one page. Well, actually a little over 2/3 of a page (once you take into account the introductory text, etc).
So I thought about it a lot. The editors wanted to show an active working environment, and so I thought about the interiors of labs for some time, looked up lots of physics breakthroughs over the years, and reflected on what might come. I eventually realized that the most important single change in the science that can be visually depicted (and arguably the single most important change of any kind) is the change that’s happened to the scientists. Most importantly, we’ve become more diverse in various ways (not uniformly across all fields though), much more collaborative, and the means by which we communicate in order to do science have expanded greatly. All of this has benefited the science greatly, and I think that if you were to get a time machine and visit a lab 30 years ago, or 30 years from now, it will be the changes in the people that will most strike you, if you’re paying attention. So I decided to focus on the break/discussion area of the lab, and imagined that someone stood in the same spot each year and took a snapshot. What we’re seeing is those photos tacked to a noticeboard somewhere, and that’s our time machine. Have a look, and keep an eye out for various details I put in to reflect the different periods. Enjoy! (Direct link here, and below I’ve embedded the image itself that’s from the magazine. I recommend reading the whole issue, as it is a great survey of the last 30 years.)
Don’t forget, today live on Science Friday we (that’s SciFri presenter Ira Flatow, producer Christie Taylor, Astrophysicist Priyamvada Natarajan, and myself) will be talking about Hawking’s “A Brief History of Time” once more, and also discussing some of the physics discoveries that have happened since he wrote that book. We’ll be taking (I think) caller’s questions too! Also we’ve made recommendations for further reading to learn more about the topics discussed in Hawking’s book.
Join us!
-cvj
(P.S. The picture above was one I took when we recorded for the launch of the book club, back in July. I used the studios at Aspen Public Radio.) Click to continue reading this post
