Longest day of the year? It sure felt like it. I spent about 6 hours of it standing high above the city in the sun talking about physics and astronomy to camera… Super tiring.
It is for a new show I’ll say more about later.
Well, I sort of disappeared there for about a week. I got lost in some really interesting physics and had a lot of fun doing it.
I kept walking away, and it kept bringing me back. There’s that fun groove one can get into that other theorists will recognise: You hit an interesting vein where you can calculate interesting results in a particular model, and you just can’t help yourself computing more and more […] Click to continue reading this post
As you know from my writings and sketches, I like to carry a notebook. People often ask me what types I use, or assume that I use the (increasingly fashionable) Moleskine books. I like Moleskine books (the little 3inx5in ones for example), and have used them a lot in the past, but actually I prefer the books by HandBook Journal Co., (made by Global Art Materials). The surface of the paper is more flexible, in my opinion. It has a little more tooth than standard Moleskine, which makes mark-making with pencil much surer, and it also takes wetting better,
so you can work with a little wetness as well, such as lots of ink, or watercolour (paint- or pencil-based). That allows for crisp drawings like the one on the right (click for larger view – more about these sketches here), right alongside physics research musings and computations in pen and ink line on the pages shown below on the left (those notes pertain to the paper I discussed here.)
I tend to carry one of the 8.25inx5.5in landscape ones (although I love the 5.5in square ones too). (See more chat about them here.) They allow a good […] Click to continue reading this post
On Tuesday I hung out with some of the Screen Junkies folks who you may know from the hilarious “Honest Movie Trailers” web series (seriously, if you’ve not seen any of them, please go right now and have a look). We had a fun chat about time travel in movies, and presenter Hal Rudnick and I bonded over various movies old and new. The final version of the show is up on YouTube (embed below), and I’m bummed that I did not get to meet the other guest, Christina Heinlein (JPL), who seems fun – and is a descendant of, yes, that Heinlein. I love the idea that she works at JPL, helping make possible the space exploration that Robert Heinlein helped inspire us all about in his writing. Anyway, enjoy the short piece (I wish you could see a bunch of the other material too… we really had a great chat about the ins and outs of time travel, but a lot of it inevitably ended up not making the cut…)
I could not resist talking about my view of this (perhaps growing) trend of using time travel as a means of resetting movie franchises (see Star Trek, X-Men…). It’s a great way of repairing writing and other filmmaking wrong turns. Feel free to imagine your own version of this – Star Wars anyone? Another pass at […] Click to continue reading this post
In fact, the last several days have felt like this, with regards big decisions about various administrative roles I’ve been asked to consider taking on. It never seems to end, and I am terrible at saying no to as many things as I should. And I have a bad habit of doing things to the best of my ability and hence I get a reputation as the guy to ask to do a task since I did a good job last time, and so it gets me sucked in deeper into the administrative quagmire, and so on and so forth.
Rather like the “entrapment events” that happened in the La Brea Tar Pits so long ago (have a read of what I wrote about those on a field trip to the Page Museum a while back). I was wandering around the LACMA and Tar Pits grounds yesterday evening after a shoot for a show (a fun thing coming that I’ll let you know about shortly) and made a phone call to say, after ten days of […] Click to continue reading this post
So it happened again. I got musing to myself about something and decided to do a quick computation to check it out, and it took me down an interesting rabbit hole, which resulted in me writing a nice little paper at the end of last week that appeared today on the arxiv. I think the physics is really really nice. Let me tell you a bit about it. It is in the same area of ideas that I mentioned last time, concerning that paper I wrote last month. So let me pick up the story there, since I did not really touch on the core of the story. [Note: for non-experts, the following will get somewhat technical and full of terms and ideas that I will not explain. Sorry.]
One of the things that might have struck you (if you’re an expert in the area) from my proposal to make heat engines out of black holes that do real mechanical work like the engines you read about in physics textbooks is that there ought to be no actual mechanical work since there’s no pistons – no pistons changing volumes and so forth. That is (or rather, was) a missing ingredient in the standard thermodynamics of black holes in quantum gravity. Well, that all changed a short few years ago with the work of a number of authors, particularly with the clear suggestion of David Kastor, Sourya Ray, and Jennie Traschen, and work by Brian Dolan, with a fair bit of followup investigations by various other authors including some I’ll mention below. (Update: Two reviews, with different foci, can be found in here and here.) The general idea is that if you allow the cosmological constant [tex]\Lambda[/tex] to be a thermodynamical variable as well (and there is a long history of authors considering this in various contexts), where it naturally acts like a pressure [tex]p = -\Lambda/8\pi G[/tex], (G is Newton’s constant, and I’m setting various other constants to unity in the usual way) then you naturally include a conjugate to that variable that should be the pressure.
For a simple static black hole like Schwarzschild, the volume turns out to the the naive volume you get by taking the radius of the black hole and forming […] Click to continue reading this post
Been a while since I got to do some sketching. It is good practice to try to do something every day, but that fell by the wayside a little as far as proper sketches went. It has been busy the last week and a bit, and my subway time has been during very busy times when there’s not enough space to get out pen and paper and sketch a person without becoming a spectacle… and during the moments where I might have caught something, I’ve actually been calculating – working out questions for the final exam in the General Relativity class, and (more recently) doing some computations for a paper I’ll tell you about shortly.
Anyway, when time is short, I sometimes like doing quick sketches with a thicker pen. Stops me from digging into the details too much. In fact, I’m really liking that as a sketch mode these days… You make your lines boldly and you’re stuck with your choices, and so it gets you thinking about what’s globally important carefully before jumping in.
It is great and satisfyingly distracting fun. Anyway, between this and that over the last day or two I did a few quick faces based on some photos I found in a […] Click to continue reading this post
The Road goes ever on and on
Down from the door where it began.
Now far ahead the Road has gone,
And I must follow, if I can,
Pursuing it with eager feet,
Until it joins some larger way,
Where many paths and errands meet.
And whither then? I cannot say.
– J.R.R. Tolkien.
It is Commencement day today at USC! In celebration of that I thought I’d post a picture of my colleague Krzysztof Pilch and I, being a bit silly. We each have one of those excellently practical Brompton bikes (splendidly finished in British racing green, of course) you sometimes have read about here, and Krzysztof suggested that we take a picture or two of us in academic robes riding our bikes. Krzysztof had his academic full gear ready because […] Click to continue reading this post
It is Commencement on Friday, here at USC. Thousands of students will be dressing up in gowns and taking part of the ceremonies marking the ending of their time here at USC and the beginning of the rest of their lives. It’s an exciting time.
Merrill Balassone and a team from USC Media Relations came by my office a few weeks ago to take 15-20 minutes of time to do a prototype of a project on this very subject of commencement. The result was fun, and apparently they used it to build onto in order to make the final short video you can see below. 
They did a great job! It is a group of USC professors and staff** giving brief thoughts to graduating students upon their graduation. You’ll maybe guess what I say in my segment. It is a theme I mention here a lot, as part of my personal war on people being shut out of (or shutting themselves out of) participation in aspects of our society.
The summary of the piece is here and the YouTube video is embedded below: […] Click to continue reading this post
…Yeah. Somehow sending proposals and samples of manuscripts around by email does not really feel super-exciting to me. But it is the way things are done now, it seems. But this afternoon, I found myself doing something very old-school, which I rather enjoyed, perhaps because it connected me with writers through the ages: Printing up some special packages (proposal, samples, etc, of the book project), putting them into envelopes and schlepping them down to the post office, getting in line, and […] Click to continue reading this post
Well, it is that time of year. The Jacarandas peaking is one of the many LA markers of the seasons for me. It means that classes will soon be over (in fact they are now) and I’ll be saying goodbye to a group of students, either because a class is over, or because students I’ve taught in earlier classes are graduating and leaving USC. Either way, it is always a time of mixed feelings, and a sense of being in transition in a number of ways. The Spring is already beginning to feel like it is rolling into Summer, and I’m clearing my desk of one set of things and making way for other things.
(Oh, and of course, the other thing that happens this year is that I seem to end up doing a post like this at around this time, right down to within a few days. It usually involves a picture of a Jacaranda tree. See here and look at the list of related posts below.)
I had an extraordinarily good group of students in my Spring class this year. As you may recall it was an undergraduate General Relativity class (see earlier posts on this by searching on that topic). We ended up having a lot of fun with the topic itself, and things were extra good because the students were very […] Click to continue reading this post
This diagram is the cycle for another heat engine (using a black hole as the working substance) that I studied in the recent paper. It is a path made of two constant pressure legs (isobars) and two constant volume legs (isochores) that happen (due to the properties of static black holes) to also be adiabats. See the post.
It got included in the paper as another example where one could compactly write down something useful about the efficiency, since, as it turns out, you can write closed form expressions […] Click to continue reading this post
On Monday 28th April at 8 PM Eastern time (5 PM Pacific) I’ll take part in a live radio interview that you might want to listen to, on a show called Alpha Centauri and Beyond. I guess I’m in the “Beyond” bit? I don’t really know anything about the show except that they like to bring people on to discuss ideas, and when I get a call to come and help sprinkle a bit of science, you know I’m likely to say yes if I can spare the time.
You can see a link to the details here, and you can listen online. As you can see it is advertised as being about me explaining string theory. Well of course that billing is nothing to do with me – I can’t hope to explain any complicated subject like that in the time available – but if asked I will do my best to try and motivate some of the ideas behind the subject. I hope it will be a fun interview and that […] Click to continue reading this post
Yes, you heard me right. Holographic Heat Engines. I was thinking recently about black holes in universes with a cosmological constant and their thermodynamics. I had an idea, it led to another, then another, then some calculations, and then a couple of days of writing, calculating, and thinking… then a day to cool off and think about other things. Then I came back to it, decided it was still exciting as an idea and so tidied it all up as a paper, made some diagrams, tidied some more, and voila! A paper submitted to the arxiv.
I’m sort of pleased with all of it since it allowed me to combine a subject I think is really fun (although often so bleakly dull when presented at undergraduate level) – heat engines – with contemporary research ideas in quantum gravity and high energy physics. So I get to draw some of the cycles in the p-V plane (graph of pressure vs volume) representing the inner workings of engines of particular designs (just like you might have seen long ago in a physics class yourself) and compute their efficiency for doing mechanical work in exchange for some heat you supply. It is fundamental that you can’t 
do that with 100% efficiency otherwise you’d violate the second law of thermodynamics – that’s why all engines have to have some exhaust in the form of heat, giving an efficiency represented by a quantity [tex]\eta[/tex] that is less than one, where one is 100% efficient. The diagram on the left illustrates the key pieces all engines must have, no matter what working substance you’re using. The details of the design of the engine are what kind of cycle you taking it through and what the properties (“equation of state”) your working substance has. In the case of a car, for example, the working substance is cleverly mixed up with the source of heat – the air/gasoline mix forms a “working substance” that gets expanded and compressed in various ways (in the green bit of the diagram), but the fact that it also burns releasing heat means it is also the source of the heat that comes into the engine (the flow from the red bit) to be (in part) turned to work, and the remainder flowing out to the blue (exhaust). Very clever.
The cool thing here is that I’m using black holes as the working substance for […] Click to continue reading this post
