Replenishing critical supplies of cinnamon-raisin bread for the household, a couple of days ago. Not a bad result, given that it is so long since I’ve made this kind of loaf. The recipe turned out a little raisin-poor for my tastes, and it was a little dry (possibly my fault), so I will be improvising some variations on the recipe and baking method to improve these aspects.
-cvj
My big task this afternoon was not baking but making a hexahexaflexagon! I can’t tell you why right now, but as far as I know it has nothing to do with my recent paper on JT gravity in case you were trying to see a connection.
-cvj
What’s that now? You want more physics teases? Ok. That dotted line is a (known) JT gravity Schwarzian spectral density. That red line? It’s the fully quantum corrected result! To all orders in topology and beyond! See my paper that appeared today on the arXiv.
(For experts: The red line is made up of about 2000 points for each of which I know the energy, and the full wave function for an associated problem. Using those I can compute lots of things, to good accuracy. One example is the full non-perturbative spectral form factor, that I showed last post.)
-cvj
Ok here goes. Been bursting to tell you this for many weeks. Ever wondered what the fully non-perturbative spectral form factor for a JT gravity model looks like? For real? Not in some special limit or simplified model? Here you go*.
Paper out on Monday! (I plan on doing a post or two about what this all means.)
–cvj
*For the experts, note that this shows both non-perturbative and strong coupling effects, which are usually hard to get at. I show how in the paper.
Can’t resist some Friday wind-down deep-dive physics humour…
-cvj
To end the week, a remarkable coincidence. This morning, I was listening to one of Wynton Marsalis’ greatest recordings, his 1983 album with the Haydn trumpet concerto in E flat major. Just found it on by accident on the radio, and found myself wondering what he’s up to these days as I have not listened to his music in a long while. Then went on a long ramble to my wife about jazz trumpeters, and classical ones, and the wonderful film score work of Terence Blanchard on all those Spike Lee films that I love, and so on. I suspect she stopped listening 20% of the way in…. Then tonight, browsing the Guardian’s website, I found – again by accident – an opinion piece from the very same Wynton Marsalis, on race and America. And it is so very well written indeed. So I thought I’d share it, before I put this all down for this evening’s big event: watching Spike Lee’s Da 5 Bloods, just out… with music by Terence Blanchard…
Enjoy.
–cvj
This Wednesday (10th June), in support of #BlackLivesMatter and the demonstrations taking part worldwide, there will be a day of action in various parts of academia to simply stop doing “business as usual” while the horrors of what is routinely done to black people at all levels of society continue.
What people choose to do on that day is up to them, but there are suggestions as a number of websites. I encourage you to go there and read what they have to say, and make up your own mind. A good start is the ShutDownStem site, and search under #ShutDownAcademia, #ShutDownSTEM and #Strike4BlackLives on social media for chatter, activity, and more resources. The Particles For Justice group, led by people in or close to my field, have also joined in to lead and encourage, and their site is here, again with lots of suggestions for types of action to get involved in.
Frankly, having seen and heard (over many cycles) a lot of rhetoric and symbolic action go nowhere on this issue, I’m not sure how I feel about this (which is partly why I’ve not posted about this for a few days since it was announced). …And I could go on at length about all the “turning points” people tell me that they can see “this time”, and how familiar it all is to me, but I won’t. I just hope that I’m wrong and that something will come of everything people are doing in their own ways. Hope is a powerful thing, and I won’t let cynicism (mine, or anyone else’s) get in the way of people trying to make a difference.
I will say that it is striking and an excellent development that people in academia, and as far removed from the everyday as particle physics, have at least recognised (this time around) that the issue is connected to them, recognized that “business as usual” is part of the problem. It’s usually easy for them to just ignore the concerns, since there are so few black people around in the corridors of academia -and especially in my field- that there’s usually nothing or nobody to remind them to stop and think about it. But of course, it’s not an accident that so few of their colleagues are black – it’s connected to the very same issue. So, great, something’s getting through, and several people are showing that they care – enough to stop what they’re doing, if just for a day, and not do “business as usual”. I respect that, and respect the people organizing this.
So have a look, and make up your own mind how/if you want to participate. Consider signing up at the Particles for Justice google page to show your support, and good luck to you.
Good luck to us all.
–cvj
(Clickable montage of some recent posts on my instagram account that might interest you. See also the twitter and Facebook accounts. Links in sidebar.)
The desire to have glitch-free online teaching and business meetings at home has driven me to do some infrastructure improvements I should have done years ago: extending the Ethernet backbone of the home network. Connecting the jacks (ethernet connectors) is a tad fiddly (but trivial), but the results are worthwhile!
In particular, it is far better (than being connected to WiFi) to have the computer connected via ethernet (had to get the appropriate dongle for my mac) when teaching via Zoom. It gives a more robust setup than you can get WiFi (unless you’re right on top of one of your WiFi transponders). Since I’ve switched to ethernet for such sessions I’ve never had even the hint of a loss of quality in my zoom session, which is important when trying to focus on the teaching subject matter, and not technology issues. I even did a radio/podcast interview the other day (online), reasonably confident that the quality was strong throughout.
There’s an ethernet connected repeater station far from the main base station, so that when it now broadcasts the network wirelessly, I there is stronger network coverage all over the house than when it was just connected over WiFi. Should have done this years ago.
-cvj
Sharing my live virtual chalkboard while online teaching using Zoom.
But the big test was this morning. Giving a two hour lecture to my General Relativity class where we were really not all in the same room, but scattered over the campus and city (and maybe beyond), while being able to maintain a live play-by-play working environment on the board, as opposed to just showing slides. Showing slides (by doing screen-sharing) is great, but for the kind of physics techniques I’m teaching, you need to be able to show how to calculate, and bring the material to life – the old “chalk and talk” that people in other fields tend to frown upon, but which is so essential to learning how to actually *think* and navigate the language of physics, which is in large part the diagrams and equations. This is the big challenge lots of people are worried about with regards going online – how do I do that? (Besides, making a full set of slides for every single lecture you might want to do For the next month or more seems to me like a mammoth task – I’d not want to do that.)
So I’ve arrived at a system that works for me, and I thought I’d share it with those of you who might not yet have found your own solution. Many of the things I will say may well be specific to me and my institution (USC) at some level of detail, but aspects of it will generalize to other situations. Adapt as applies to you.
Do share the link to this page with others if you wish to – I may well update it from time to time with more information.
Here goes:
How do I prepare my research talks? I usually just sit down with a pencil, some paper and a cup of something warm, and I just draw/map out the story. Each box is a beat of the narrative, and ends up corresponding to one or two slides (if I’m doing slides). Then I’m more or less done.
(The facility of this old school approach is that drawing it out keeps it visual, less heavy with equations. Too many (if any) slides or long periods laden with equations (at least in physics) just aren’t so great. Also, it allows me to move these thumbnails/pages/sketches around if I need to, to sculpt the narrative. I can sit back and see if it’s all there at the end.)
(For this Harvard/MIT seminar, scheduled for Wednesday, I don’t yet know if I am going to get to give it. Wisdom about travel and gatherings is a bit uncertain right now, and things are changing as I type. Decisions on Monday. Update:- we changed it to a remote talk.)
–cvj
When looking for an excuse to have some custard, simply whip up an upside down cake built on a bit of fruit, spices, and whatnot you might have (here: apples cooked in butter, basking on caramel, with toasted walnuts, cinnamon…etc).
–cvj
Updated with lots of new results! For your reading pleasure as 1912.03637 on the arXiv. (And still a swift read at 14 pages.)
New results include a fascinating differential equation for spectral densities, and some lovely E=0 results.
#physics #blackholes #gravity
–cvj
Here’s a striking coincidence. Last Friday I was preparing to deliver a lecture on special relativity to my undergrad General Relativity class with this Hobbity thought experiment (that helps one discover Lorentz-Fitzgerald contraction), when I heard that Christopher Tolkien (the boy the Hobbit was originally written for) had died. (RIP. And thanks for the maps, the Silmarillion and so much more.)
I took the opportunity in class to pay brief tribute to him and to encourage a new generation to delve into the books, the world, and more, as expanded and illuminated for us by Tolkien the younger.
-cvj
(A somewhat more technical post follows.)
Continuing from part I: Well, I set the scene there, and so after that, a number of different ideas come together nicely. Let me list them:
What “nearly” AdS_2 looks like via JT gravity. The boundary wiggles, but has fixed length 1/T.
, by solving the Schwarzian dynamics for the wiggling boundary that I mentioned earlier. (The interior has a model of gravity on 
, as I mentioned before, but as we’re in 2D, there’s no local dynamics associated with that part. But we’ll see in a moment that there’s very interesting stuff to take into account there too.) Anyway, the result for the Schwarzian dynamics can be written (see Stanford and Witten) in a way familiar from standard, say, statistical mechanics: 
, where 
is the spectral density of the model. I now need to explain why everything has a subscript 0 in it in the last sentence.
, where 
are the number of handles, boundaries, and crosscaps the surface has, characterising its topology. Forget about crosscaps for now (that has to do with unorientable surfaces like a möbius strip 
– we’ll stick with orientable surfaces here). The full JT gravity action therefore has just the thing one needs to keep track of the dynamics of the quantum theory, and the partition function (or other quantities that you might wish to compute) can be written as a sum of contributions from every possible topology. So one can write the JT partition function as 
where the parameter 
weights different genus surfaces. In that sum the weight of a surface is 
and 
since there’s a boundary of length 
, you may recall.
The basic Schwarzian computation mentioned above therefore gives the leading piece of the partition function, i.e., 
