A lot of us have been waiting for a long time to hear this news! The NANOGrav collaboration has announced strong evidence of a background of low frequency gravitational waves emitted from supermassive black hole mergers. Their detection methods are pulsar timing arrays (still one of those fantastically simple, cool … 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
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
Between 3 and 4 pm Eastern time today (very shortly, as I type!) I’ll be answering questions about Hawking’s “A Brief History of Time” as part of a Live twitter event for Science Friday’s Book Club. See below. Come join in! Hey SciFri Book Clubbers! Do you have had any … Click to continue reading this post
Friday will see me busy in the Radio world! Two things: (1) On the WNPR Connecticut morning show “Where We Live” they’ll be doing Summer reading recommendations. I’ll be on there live talking about my graphic non-fiction book The Dialogues: Conversations about the Nature of the Universe. Tune in either … Click to continue reading this post
Turns out that Frank Buckley, the news anchor at KTLA 5, is not just a really great guy (evident from his manner on TV), but also a really excellent interviewer with a sharp curiosity that gives me hope that great journalism is still alive, well, and in good hands. I showed up at the station expecting to just have a pleasant chat around the book and be done with it, but I walked into the room and he’d done all his research and was sitting with extensive notes and so forth about lots of physics ideas he’d read in the book that he wanted to talk about! So we have a blast talking about the physics of our universe and the world around us in some in-depth detail. It was fantastic, and just the kind f conversation I hope that the book celebrates and inspires people to have!
Check out our interview here (embed below), and be sure to tune in to his […] Click to continue reading this post
(Process from the book.)
The book is appearing on bookshelves in the UK this week! Warehouses filling up for UK online shipping too.
Dear colleagues far and wide. I’m delighted to share the news that we are having a job search in Astrophysics! Please note the link’s contents, and share it to those who might be interested. Thanks! https://usccareers.usc.edu/job/los-angeles/assistant-professor-of-physics-and-astronomy/1209/5668638 -cvj
Since the early Summer I’ve been working (with the help of several people at USC*) toward a big event next Friday: A celebration of 100 years since Einstein formulated the field equations of General Relativity, a theory which is one of the top one or few (depending upon who you argue with over beers about this) scientific achievements in the history of human thought. The event is a collaboration between the USC Harman Academy of Polymathic Study and the LAIH, which I co-direct. I chose the title of this post since (putting aside the obvious desire to resonate with a certain great work of literature) this remarkable scientific framework has proven to be a remarkably robust and accurate model of how our universe’s gravity actually works in every area it has been tested with experiment and observation**. Despite being all about bizarre things like warped spacetime, slowing down time, and so forth, which most people think is to do only with science fiction. (And yes, you probably test it every day through your […] Click to continue reading this post
Here, as promised yesterday, is the fun conversation at Screen Junkies. I don’t need to say much, since much of what I wanted to talk about (extra dimensions, other laws of physics, parallel universes, etc) made it to the (awesomely cut, btw!) episode! Embed of video below.
Enjoy! […] Click to continue reading this post
Here’s some interesting Sunday reading: Frank Close wrote a very nice article for Prospect Magazine on the business of testing scientific theories in Physics. Ideas about multiverses and also string theory are the main subjects under consideration. I recommend it. My own thoughts on the matter? Well, I think most … Click to continue reading this post
…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 to
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
Here’s Robbert Dijkgraaf, Director of the Institute for Advanced Study (Princeton), giving a lecture on aspects of the nature of Light and its role in the universe at the kick off of the International Year of Light in Amsterdam. He’s always an excellent speaker, so sit back and enjoy this 15 minutes.
Found in the box for a ball I bought. Wondering if perhaps our Universe was made by the same company…
-cvj
P.S. Concerned now, because this was a replacement ball. The first one developed a mysterious rift in its fabric and rapidly deflated.
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