Show HN: Physically accurate black hole you can put in your room • Hacker News Board

Re: Show HN: Physically accurate black hole you can put in your room

#201

Post by aplavin » Sat, Aug 01, 2026, 8:50 PM UTC

KaiserPro wrote: post #83

20k wrote: post #34

If anyone's interested in the accuracy, this is very 'visualisation grade' software. Its a bit of a pet peeve of mine that people present these sims as being very physically accurate, when they contain major inaccuracies, some of which are very obvious and/or deliberate. This one has some serious physical limitations I wouldn't mind at all if it didn't say that this was a *physically accurate* black hole specifically…

I clicked on this because I worked on the infra that simulated the famous blackhole sim in interstella. I thought "oooh this is interesting I wonder how they are going to do physically accurate on an end device" Recalling how the original particle sim was something like 100TB, took 2 weeks to generate and seemed to write in a way that killed disks. but that was >10 years ago, so what clever stuff has been done to mod…

> I thought "oooh this is interesting I wonder how they are going to do physically accurate on an end device" Recalling how the original particle sim was something like 100TB, took 2 weeks to generate and seemed to write in a way that killed disks. but that was >10 years ago, so what clever stuff has been done to model it locally.

Yes, totally reasonable question! Those terabytes surely were things like fluid/matter motion around the black hole, stuff like this.

Here, I definitely don't simulate matter motion around the black hole as a particle/fluid sim does – instead, I focus on simulating the effects of the black hole itself. Matter distribution and motion (where it is used at all, ie not in camera mode) is described by simple functions phenomenologically.

The single most notable effect of a black hole is strong light bending (+ time delays), and it is properly simulated in all modes in this app. Next, relativistic beaming (Doppler boosting) and gravitational redshift are simulated for the accretion disk emission as well. If you zoom out, the jet is visible as well – it's relatively far away, so it is rendered with special relativity only; ie, no GR, but full volumetric rendering taking all SR effects into account. Admittedly, the GR-SR seam implementation can be improved somewhat.

Re: Show HN: Physically accurate black hole you can put in your room

#202

Post by nnevatie » Mon, Aug 03, 2026, 5:44 AM UTC

aplavin wrote: post #200

nnevatie wrote: post #194

Earlier quoted context omitted.

This is on Chrome/Win11: https://snipboard.io/W8SXYm.jpg

Hmmm I think I see what's happening here. Basically, all devices I tested (laptops/phones/tablets) seem to have small pixel size, and to save on compute power for weaker devices I decided to render with half as many pixels as the screen has, letting the browser upscale the result. In your case, pixels are probably quite a bit larger, and half-res rendering has these prominent artifacts. Can you try if increasing "ren…

Setting render scale to 1 definitely helped - the aliasing from the lines is gone.

The rest of the circular aliasing could likely be fixed by requesting MSAA, so e.g.:

renderer = new THREE.WebGLRenderer({ alpha: true, antialias: true, powerPreference: 'high-performance', })

Re: Show HN: Physically accurate black hole you can put in your room

#203

Post by aplavin » Tue, Aug 04, 2026, 1:09 AM UTC

nnevatie wrote: post #202

aplavin wrote: post #200

Earlier quoted context omitted.

Hmmm I think I see what's happening here. Basically, all devices I tested (laptops/phones/tablets) seem to have small pixel size, and to save on compute power for weaker devices I decided to render with half as many pixels as the screen has, letting the browser upscale the result. In your case, pixels are probably quite a bit larger, and half-res rendering has these prominent artifacts. Can you try if increasing "ren…

Setting render scale to 1 definitely helped - the aliasing from the lines is gone. The rest of the circular aliasing could likely be fixed by requesting MSAA, so e.g.: renderer = new THREE.WebGLRenderer({ alpha: true, antialias: true, powerPreference: 'high-performance', })

Would MSAA compute more samples, effectively multiplying shader computation? Ideally, it should be something adaptive, to the number of pixels/device compute power, eg compute 2x smaller resolution on phones/retina, compute 1x resolution on larger-pixel screens, and maybe even 1x + MSAA beyond some pixel sizes... Just wanted to avoid reinventing these heuristics.

Re: Show HN: Physically accurate black hole you can put in your room

#204

Post by aplavin » Tue, Aug 04, 2026, 1:14 AM UTC

aizk wrote: post #9

Very cool, and very mind bending. Very faithful to the Event Horizon Telescope rendering. A decade ago I got really into black holes for like a few months, and I read Kip Thorne's book called "The Science of Interstellar", talking all about black hole simulations. Have you read it? I wonder how the simulation tech has evolved, as 10 years is a lot. I do wonder if you do like, size estimates of a black hole in my room…

> I do wonder if you do like, size estimates of a black hole in my room. Suppose I have a black hole in my room, I'd be curious to know what the mass of that is, like a fun fact, tidbit somewhere.

Forgot to answer this first!

Basically, ~1 cm radius black hole has the mass of the Earth – really, Earth would need to get this small to become a black hole. I've made a very simple demo for a kids lecture I gave recently, https://plav.in/outreach_demos/squeeze-earth-v2.html. Also see https://xkcd.com/1680/ of course :)