Matrices and Gravity

So I have a confession to make. I started working on random matrix models (the large $latex N$, 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 $latex N$ 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.

Let me tell you a little more. […] Click to continue reading this post

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 […] Click to continue reading this post

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


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.) -cvj


[caption id="attachment_19762" align="aligncenter" width="499"]Jupiter and Saturn 21st December 2020 Jupiter (with some moons) and Saturn, 21st December 2020 (click for larger view) [/caption]

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 […] Click to continue reading this post

Winds of Change!

[caption id="attachment_19735" align="aligncenter" width="499"]Montage of broken telescope parts Broken Telescope![/caption]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 […] Click to continue reading this post