Matrices and Gravity

[A somewhat more technical post follows.]

So I have a confession to make. I started working on random matrix models (the large N, double-scaled variety) in 1990 or 1991, so about 30 years ago, give or take. I’ve written many papers on the topic, some of which people have even read. A subset of those have even been cited from time to time. So I’m supposed to be some kind of expert. I’ve written extensively about them here (search for matrix models and see what comes up), including posts on how exciting they are for understanding aspects of quantum gravity and black holes. So you’d think that I’d actually done the obvious thing right? Actually taken a bunch of random matrices and played with them directly. I don’t mean the fancy path integral formulation we all learn, where you take N large, find saddle points, solve for the Wigner semi-circle law that the Dyson gas of eigenvalues forms, and so forth. I don’t mean the Feynman expansion of that same path integral, and identify (following ‘t Hooft) their topology with a tessellation of random 2D surfaces. I don’t mean the decomposition into orthogonal polynomials, the rewriting of the whole problem at large N as a theory of quantum mechanics, and so forth. No, those things I know well. I just mean do what it says on the packet: close your eyes, grab a matrix out of the bag at random, compute its eigenvalues. Then do it again. Repeat a few thousand times and see that all those things in the data that we compute those fancy ways really are true. I realized the other day that in 30 years I’d never actually done that, and (motivated by the desire to make a simple visual illustration of a point) I decided to do it, and it opened up some wonderful vistas.

Click to continue reading this post

Some Media!

photo of microphone and headphonesAll of a sudden several bits of media I’ve been involved with are appearing at once. Two of them are as follows:

* I had a lovely chat with Brianna Barbu of Symmetry Magazine about science, art, and science communication (particularly science advising for movies). She wrote a piece on our conversation here.

* There’s another piece, focusing on science advising for movies, written by Molly Glick for Discover Magazine. Some of my work is mentioned. One aspect I like about this piece (compared to many about science advising for `Hollywood’) is that it emphasizes that there are many scientists (and sciences) involved in the process, as opposed to having one of those “this is the guy Hollywood calls!” headlines that I am not a huge fan of. It is here.

(I think there are some more coming up very soon, including some great podcast conversations. Check back here and/or follow on social media for updates. Links in sidebar.)



A Dialogue about Art and Science!

On Saturday (tomorrow), I’ll be talking with science writer Philip Ball at the Malvern Festival of Ideas! The topic will be Science and Art, and I think it will be an interesting and fun exchange. It is free, online, and starts at 5:15 pm UK time. You can click here for the details.

I’ll talk a little bit about how I came to create the non-fiction science book The Dialogues, using graphic narrative art to help frame and drive the ideas forward, and how I really wanted to re-shape what is the norm for a popular science book, where somehow using just prose to talk about serious scientific ideas has become regarded as the pinnacle of achievement – this runs counter to so many things, not the least being the fact that scientists themselves don’t just use prose to communicate with each other!

But anyway, that’s just the beginning of it all. Philip and I will talk about the intersection of science and art in several different spheres, I imagine. Art is a powerful tool for helping communicating science, for engaging people with science… but it is (in my view) a big mistake to think of it (as most scientists do) as mere decoration – it can be a major component of the tools we use to drive scientific discovery too! Maybe more recognition of that will help enhance scientific discovery, since the toolbox is enhanced, *and* through broader kinds of skillsets people have that are useful for science. I hope we get to talk about that too!

Go ahead and register for (free) access to the event, and I’ll see you there! Philip and I will be signing books after, I think. We’ll sign bookplates that will be attached to books that you order, and then it get sent to you. Details on the festival site.


Full Circle

snapshot of paper

Yesterday I submitted (with collaborators Felipe Rosso and Andrew Svesko) a new paper to the arXiv that I’m very excited about! It came from one of those lovely moments when a warm flash of realisation splashed through my mind, and several fragments of (seemingly separate things) that had been floating around in my head for some time suddenly all fit together. The fit was so tight and compelling that I had a feeling of certainty that it just “had to be right”. It is a great feeling, when that happens. Of course, the details had to be worked out, and everything checked and properly developed, new tools made and some very nice computations done to unpack the consequences of the idea… and that’s what resulted in this paper! It is a very natural companion to the cluster of papers I wrote last year, particularly the ones in May and June.

What’s the story? It’s all about Jackiw-Teitelboim (JT) gravity, a kind of 2D gravity theory that shows up rather generically as controlling the low temperature physics of a wide class of black holes, including 4D ones in our universe. Understanding the quantum gravity of JT is a very nice step in understanding quantum properties of black holes. This is exciting stuff!

Ok, now I’ll get a bit more technical. Some background on all this (JT gravity, matrix models, etc), can be found in an earlier pair of posts. You might recall that in May last year I put out a paper where I showed how to define, fully non-perturbatively, a class of Jackiw-Teitelbiom (JT) supergravity theories that had been defined in 2019 in a massive paper by Stanford and Witten (SW). In effect, I showed how to build them as a particular combination of an infinite number of special “minimal string” models called type 0A strings. Those in turn are made using a special class of random matrix model based on Click to continue reading this post


Work in progress on a drawing of a character from a book you may know…

Revisiting an old friend you might recognize. (And discovering that my old inking/shading workflow was just fine. – I’d been experimenting with other approaches and also just getting back into the saddle, as it were. I’ve found that I’d already landed on this approach for good time-cost/benefit reasons.)



Jupiter and Saturn 21st December 2020

Jupiter (with some moons) and Saturn, 21st December 2020 (click for larger view)

But… while the viewing on the 21st (the peak of the conjunction) was perfect, seeing three of the Galilean moons, and the glorious rings of Saturn, very clearly, getting a decent through-the-lens photo was not so trouble-free. I was dissatisfied with the roughs of the photos I got that night, with lots of blurring and aberrations that I felt I should have been able to overcome. So I spent the next day taking the telescope entirely apart, checking everything, and trying to colimate it properly, and testing schemes for better vibration stabilisation of the camera. I was ready for another session of photographing the next night, but it was cloudy, with only about ten minutes where there was a view of the planets, and only then through a thick layer of cloud. The next two nights were even more cloudy. But Christmas day had lovely clear evening skies for a good long while, and so I took lots of photos. But they were all still not really very good – I expected that as I’d not solved the colimation problem properly, perhaps because of the damage from the fall – and while I reduced vibration a lot, my exposure times were poorly chosen, and I ended up with motion blurring on top of everything else.

So today I went back to the ones I took on Monday at the height of the conjunction and found that they were not as terrible as I’d thought originally, if I did a bit of rough selective filtering help in photoshop to adjust colour and exposure for the three main elements (the two planets, and the moons). I had to bring down the exposure on Jupiter as compared to Saturn, and then of course the moons disappeared, so I had to bring those up a bit. Then I had to remove (a little bit) some colour problems on Jupiter and the moons due to chromatic aberration.

So, subject to focusing and colimation difficulties with the telescope, this (at the top of the post) is my best offering of the conjunction on the night. I’m glad to have some kind of personal record of the lovely event.


Repaired and Ready!

Well, I did what I said I’d try in the previous post. And it worked! I had a great time viewing the conjunction. I hope you did too if you found a moment and clear skies My photography was hampered by either poor stabilisation of the camera or a misalignment of the telescope (due to the fall?) so my photos were not very good. I will do some daytime experiments and then try again this evening. The fact is that if you missed it last night it will probably be just as good again tonight, and for some nights to comes, just as is it was on the nights leading up to the closest approach. Just because it is not in the news any more does not mean it is not still spectacular!


Winds of Change!

Montage of broken telescope parts

Broken Telescope!

There’s an exciting astronomical conjunction tonight! Jupiter and Saturn (that you may have noticed have been approaching each other in the sky steadily over the course of the year) will be at their closest approach! It has already been a lovely sight in the evening sky over the last many days. Since I’d been doing a bit of observation and photography of each planet in July (click on the two below for some blurry (but exciting to me) offerings…see more photos I shared on social media – I don’t think I posted them directly here), I’ve been wondering what sort of views I might be able to photograph at this closest approach.

Saturn and rings photo from July Jupiter and four moons in July

Well, there was a bit of a disaster a month ago that I neglected to tell you about. A day or few after the US election, there was a major freak windstorm, just for a short while. I remember joking that it was the winds of change coming through. But then I heard an almighty crash from above that shook the house. I went to the roof and the entire telescope and tripod had (despite being weighted down) blown over and had crashed to the ground! There was considerable damage. See photo montage above – click for larger view.

So I currently have no means to look at the conjunction close up! I’ve been testing the optics (miraculously the mirrors seem intact, but the main tube is quite dented, with the finder scope almost broken off) and it seems ok, but the legs have been torn/broken off the tripod, so I cannot support and point the instrument.

There may be hope though! Out of desperation I ordered a tripod two days ago that looks like it has legs that I can cannibalise to use on to the old assembly, and they are set to arrive soon, so we will see if I am lucky. Maybe I will be able to photograph the conjunction after all – if it is not too low in the sky to be seen from my vantage point.