lupsasca

Hi, I'm an author on the paper. It was definitely a human-AI collaboration, but it is also true that the final simplified formula, Eq. 39 in the paper (which is what we had been seeking, without success), was conjectured and proved by GPT. So it derived a new result in theoretical physics. I'm genuinely puzzled by your complaint.

Correct, on both counts!

My pleasure---thank you for your interest!

There are closely related "MHV amplitudes" which naively obey a really complicated formula, but for which there famously also exists a much simpler "Parke-Taylor formula". Alfredo had derived a complicated expression for these new "single-minus amplitudes" and we were hoping we could find an analogue of the simpler "Parke-Taylor formula" for them.

That paper from the 80s (which is cited in the new one) is about "MHV amplitudes" with two negative-helicity gluons, so "double-minus amplitudes". The main significance of this new paper is to point out that "single-minus amplitudes" which had previously been thought to vanish are actually nontrivial. Moreover, GPT-5.2 Pro computed a simple formula for the single-minus amplitudes that is the analogue of the Parke-Taylor formula for the double-minus "MHV" amplitudes.

Hi I am an author of the paper. We believed that a simple formula should exist but had not been able to find it despite significant effort. It was a collaborative effort but GPT definitely solved the problem for us.

By "grabbing references" I meant queries of the type "add paper [bla] to the bibliography" -- that seems useful to me!

I am very sympathetic to your point of view, but let me offer another perspective. First off, you can already vibe-write slop papers with AI, even in LaTeX format--tools like Prism are not needed for that. On the other hand, it can really help researchers improve the quality of their papers. I'm someone who collaborates with many students and postdocs. My time is limited and I spend a lot of it on LaTeX drudgery that can and should be automated away, so I'm excited for Prism to save time on writing, proofreading, making TikZ diagrams, grabbing references, etc.

About ~5x improvement. Recall that the resolution of an interferometric array is set by the distance between telescopes measured in units of the observation wavelength. BHEX will get a ~3x resolution improvement from the increased distance between the space satellite and our ground telescopes (for the EHT, the max telescope separation is limited by the diameter of the Earth) and another ~50% from the increased frequency of observations (going up from 230 to 320 GHz).

5x is actually a lot: we'll be able to resolve the "photon ring" of orbiting light around M87* and Sgr A* (the two black holes previously imaged by EHT at lower resolution) and likely see the "shadows" of another 6-8 black holes, with the possibility of estimating the mass of another ~20-30 sources.

We're thinking about it! Likely 2025 though.

If you put the source infinitely far away (as we are doing here) and at zero velocity relative to the camera, then there is no redshift effect at all, so you could say that this is the choice of redshift that we made :)

If you want the details, they're too long to put in this comment but essentially what I mean is that the r->infty limit of the redshift factor in Eq. (B22) of this paper is unity: https://arxiv.org/abs/2211.07469

Not currently. As I mentioned elsewhere, the rotating black hole version that we implemented requires GPU code, and porting that to Android is nontrivial---though we'd love it if someone took our open-source code and ported it!

In the meantime, check out this code developed by Dominic Chang (grad student at Harvard) that implements lensing by a non-rotating (Schwarzschild) black hole in your browser: https://dominic-chang.com/bhi-filter/

Excellent! Hope it looked cool.

Hahaha, I half-expected a plasma physicist to complain that GRRMHD is not self-consistent and we need to include non-ideal fluid effects :D

That would be cool, but then you wouldn't be seeing the world around you anymore. In other words, at that point it becomes a GRMHD simulation, and there is no point in using cameras since the user's environment is obscured, no? Or did you have something else in mind?

I haven't looked into the equations but I expect the effect of varying the electric charge would be similar to (but less dramatic than) changing the spin of the black hole, which as you can see in our app is not that big of a change.

The rotating black hole version that we implemented requires GPU code, and porting that to Android is nontrivial---though we'd love it if someone took our open-source code and ported it!

In the meantime, check out this code developed by Dominic Chang (grad student at Harvard) that implements lensing by a non-rotating (Schwarzschild) black hole in your browser: https://dominic-chang.com/bhi-filter/

What the black hole looks like depends on how you define your field of view. And if the black hole is spinning, then you don't expect a circular shadow at all. But in our app, if you pick the "Static black hole" (the non-rotating, Schwarzschild case) and select the "Full FOV" option, then you will see the circular shadow that you expect.

Yes, this is one of the wonderful crazy properties of black holes: they get hotter as they evaporate! (More precisely, the Hawking temperature is inversely proportional to the mass!)

Glad to hear that! You'll probably also enjoy reading about the Black Hole Explorer (BHEX): a proposed space mission that will take the sharpest images in the history of astronomy and resolve the "photon ring" of orbiting light around a black hole. https://www.blackholeexplorer.org/

I think what he showed you was likely a version of this that was coded up by Harvard graduate student Dominic Chang: https://dominic-chang.com/bhi-filter/

It works very well (and in a browser!) but is limited to a non-rotating (Schwarzschild) black hole---we really wanted to include black hole spin (the Kerr case). As we write on the github, talking with Dominic about his implementation was very useful and we are hoping to get a paper explaining both codes out before the end of the year.

Yes, Andy has been very involved in the story of the photon ring and was one of the lead authors on the original paper that started it all: https://www.science.org/doi/10.1126/sciadv.aaz1310

(And he was also my PhD advisor.)

There are other apps out there for this kind of black hole vision...

Yes, but one issue is that the amount of redshift depends on the motion of the emitter, so we would have to artificially assign some four-velocity to your surroundings in order to give them some redshift. There doesn't seem to be a "natural" choice for how to do this.

TLDR: redshift depends not only on the position of the source, but also its velocity.

As Project Scientist for BHEX, I am of course excited about the project and eager to spread the word about it! But as I wrote in my other comment, what this is really trying to "sell" is gravitational physics to students interested in black holes, and this effort is supported in part by the National Science Foundation.

Adding options to drop the multi-camera view and to capture a screenshot is relatively straightforward, and I think we can implement that in the next update. Pinning the black hole to a specific place is a whole other undertaking...

Yes, such a great game---it's a fantastic visualization of special relativity and also fun to play!

I think we're still a ways off from real time GRMHD sims, but CK Chan from UArizona had a working VR simulation (on the Oculus iirc, but now deprecated) that allowed you to explore a pre-existing GRMHD simulation in real time and in 3D. I think he might be working on a new version of this.

Glad it worked on second boot! We used to have some bugs in the elliptic integral implementation that led to the app crashing, but we think we've eliminated those, so hopefully this is just a fluke... Anyone else with this issue?

Glad to hear you're excited about BHEX---we are too!

If you want to read more about what it's going to do, I wrote a blog post about it on the mission website: https://www.blackholeexplorer.org/bhex-blog/lupsasca-stateme...

The black hole simulation that was shown in the movie Interstellar is explained in detail in this paper, freely available on the arXiv: https://arxiv.org/abs/1502.03808

As a physicist with a modest background in computing, I was also surprised by how powerful the iPhone GPU is. It can indeed lens the input from the camera at high resolution and in real time with high FPS.