OMG I actually just submitted an actual paper, with me as first author. I submitted to the AAS Journals, with a preference for The Astronomical Journal. I don't write all that many first-author papers, so I am stoked about this. If you want to read it: It should come out on arXiv within days, or if you want to type pdflatex a few times, it is available at this GitHub repo. It is about how to combine many shifted images into one combined, mean image.


IAIFI Symposium, day two

Today was day two of a meeting on generative AI in physics, hosted by MIT. My favorite talks today were by Song Han (MIT) and Thea Aarestad (ETH), both of whom are working on making ML systems run ultra-fast on extremely limited hardware. Themes were: Work at low precision. Even 4-bit number representations! Radical. And bandwidth is way more expensive than compute: Never move data, latents, or weights to new hardware; work as locally as you can. They both showed amazing performance on terrible, tiny hardware. In addition, Han makes really cute 3d-printed devices! A conversation at the end that didn't quite happen is about how Aarestad's work might benefit from equivariant methods: Her application area is triggers in the CMS device at the LHC; her symmetry group is the Lorentz group (and permutations and etc). The day started with me on a panel in which my co-panelists said absolutely unhhinged things about the future of physics and artificial intelligence. I learned that many people think we are only years away from having independently operating, fully functional aritificial physicists that are more capable than we are.


IAIFI Symposium, day one

Today was the first day of a two-day symposium on the impact of Generative AI in physics. It is hosted by IAIFI and A3D3, two interdisciplinary and inter-institutional entities working on things related to machine learning. I really enjoyed the content today. One example was Anna Scaife (Manchester) telling us that all the different methods they have used for uncertainty quantification in astronomy-meets-ML contexts give different and inconsistent answers. It is very hard to know your uncertainty when you are doing ML. Another example was Simon Batzner (DeepMind) explaining that equivariant methods were absolutely required for the materials-design projects at DeepMind, and that introducing the equivariance absolutely did not bork optimization (as many believe it will). Those materials-design projects have been ridiculously successful. He said the amusing thing “Machine learning is IID, science is OOD”. I couldn't agree more. In a panel at the end of the day I learned that learned ML controllers now beat hand-built controllers in some robotics applications. That's interesting and surprising.


The Cannon and El Cañon

At the end of the day I got a bit of quality time in with Danny Horta (Flatiron) and Adrian Price-Whelan (Flatiron), who have just (actually just before I met with them) created a new implementation of The Cannon (the data-driven model of stellar photospheres originally created by Melissa Ness and me back in 2014/2015). Why!? Not because the world needs another implementation. We are building a new implementation because we plan to extend out to El Cañon, which will extend the probabilistic model into the label domain: It will properly generate or treat noisy and missing labels. That will permit us to learn latent labels, and de-noise noisy labels.


black holes as the dark matter

Today Cameron Norton (NYU) gave a great brown-bag talk on the possibility that the dark matter might be asteroid-mass-scale black holes. This is allowed by all constraints at present: If the masses are much smaller, the black holes evaporate or emit observably. If the black holes are much smaller, they would create observable microlensing or dynamical signatures.

She and Kleban (NYU) are working on methods for creating such black holes primordially, by modifying hte potential at inflation, creating opportunities for bubble nucleations in inflation that would subsequently collapse into small black holes after the Universe exits inflation. It's speculative obviously, but not ruled out at present!

An argument broke out during and after the talk whether you would be injured if you were intersected by a 1020 g black hole! My position is that you would be totally fine! Everyone else in the room disagreed with me, for many different reasons. Time to get calculating.

Another great idea: Could we find stars that have captured low-mass black holes by looking for the radial-velocity signal? I got really interested in this one at the end.


APOGEE spectra as a training set

I spent a lot of the day building a training set for a machine-learning problem set. I am building the training set out of the SDSS-V APOGEE spectra, which are like one-dimensional images for training CNNs and other kinds of deep learning tasks. I wanted relatively raw data, so I spent a lot of time going deep in the SDSS-V data model and data directories, which are beautiful. I learned a lot, and I created a public data set. I chose stars in a temperature and log-gravity range in which I think the APOGEE pipelines work well and the learning problem should work. I didn't clean the data, because I am hoping that contemporary deep learning methods should be able to find and deal with outliers and data issues. If you want to look at my training set (or do my problem set), start here.


getting the absolutely rawest APOGEE data

I spent time today (at the bar!) understanding the data model and directory structure for the raw, uncalibrated APOGEE data. The idea is that I want to do a real-data example for my paper with Casey (Monash) on combining spectra, and I want to get back to the raw inputs. I also might use these spectra for a problem set in my machine-learning class. The code I wrote is all urllib and request and re, because I think it is necessary to read directories to understand the data dependencies in the survey. Is that bad?

Putting aside my concerns: The coolest thing about this project is that the SDSS family of projects (currently SDSS-V) puts absolutely every bit of its data on the web, in raw and reduced form, for re-analysis at any level or stage. That's truly, really, open science. If you don't believe me, check out this this code that spelunks the raw data. It's all just URL requests with no authentication!


combining spectral exposures

I wrote words! I got back to actually doing research this week, in part inspired by a conversation with my very good friend Greg McDonald (Rum & Code). I worked on the words in the paper I am finishing with Andy Casey (Monash) about how to combine individual-visit exposures into a mean spectrum. The biggest writing job I did today was the part of the paper called “implementation notes”, which talks about how to actually implement the math on a finite computer.