You mean, without a camera and a screen, out of pure physical objects? You can actually reproduce gravitational light bending quite accurately with a properly-shaped lens (some wine glasses are surprisingly close!), see eg https://www.youtube.com/watch?v=PviYbX7cUUg for a classical wine glass experiment, or https://sites.google.com/view/jeansurdej/gravitational-lense... for purpose-made lenses. It only reproduces the so-called "weak field" bending, not light that makes half a turn (coming from behind you) or more.
> why the stars surrounding the black hole are just points, and more over why the lines are straight to the centre of the hole
Sorry for confusion! Points + lines are just other users looking at the black hole right now, their camera locations and lines of sight. Nothing more! In the first hours of HN frontpage, there were a lot – and I can see how one can understand them as parts of actual scene :)
I decided not to change their style, not to make them more subtle – half a day later, there are already way fewer users online, and these points/lines don't look as crowded as they did.
Hmm, interesting! I saw that it's a draft, and didn't investigate further. Maybe it does work indeed on some browsers.
Generally, the compatibility story turned out more fragmented than I expected. Eg, on my phone, Chrome can do AR – but cannot do two camera feeds at once; while Firefox is the exact opposite – no AR but can do both cameras at once, so that you see both front and rear lensed around the black hole properly (in the camera mode).
If this app turns the entire screen black, this probably means WebGL is not supported :)
Black holes don't really "suck in" light. Whatever falls onto the black hole itself gets deleted, of course – but otherwise, it bends light rays towards its center. That's why the app shows distortion + black circle in the in middle in the camera mode.
The event horizon for even the smallest black hole is in the scale of kilometers. If the user is a meter away from the black hole light isn't going to move away from the center of it to your camera.
Now I think I see what you meant.
There actually are no upper/lower limits on the black hole size (in classical physics – ignoring quantum effects). Compressing the Earth to ~1 cm in size would give you a black hole, and its event horizon size would be ~1 cm, not kilometers.
And even black holes this small are stable, according to our physics knowledge.
I grew up with micro black holes being a possibility, with conjectures such as primordial black hole evaporating down to Planck dimension stability, etc.
Yes, linked in the readme! They simulate light bending, but ignore time delay effects.
I think the earliest of these black-hole-camera renderings is https://dominic-chang.com/bhi-filter/ though (also linked in readme) – a direct inspiration for the camera mode in my app!
The technology has come a long way indeed! The first simulations of how a black hole would look like are from 1979, by Jean-Pierre Luminet – take some time to find and look at them, it's super impressive what they achieved using that era tech!
Now, we can get much higher-resolution ones in real time on any smartphone.
I work in the Event Horizon Telescope, studying jets accelerated by black holes, and immediate black hole surroundings as well. I do ray tracing / radiative transfer simulations, and this app is an adaptation of those simulations – with the primary focus on being physically accurate under reasonable assumptions.
And totally, I enjoyed listening to Kip Thorne's lectures and talking to him, he gives them in a very approachable style while remaining honest!
In my experience, on Android, it definitely relies on camera: AR doesn't work in dark room, and barely works in slightly-lit room. So it must be fusing camera + accelerometer + ...
