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Show HN: Physically accurate black hole simulation using your iPhone camera

(apps.apple.com)
313 points yunyu | 5 comments | 19 Nov 24 17:06 UTC | HN request time: 0.001s | source
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bryant ◴[19 Nov 24 17:22 UTC] No.42185902[source]▶
Neat. I'll probably use it for five minutes, appreciate the math that went into it, and move on. But nevertheless, pretty neat.

I say that because there's an idea to play with for a v1.1 that would give it staying power for me:

Do you have enough processing power on an iPhone to combine this with Augmented Reality? That is to say: can you explore "pinning" a singularity in a fixed region of space so I can essentially walk around it using the phone?

Assuming that's possible, you could continue evolving this into a very modest revenue generating app (like 2 bucks per year, see where it goes?) by allowing for people to pin singularities, neutron stars, etc. around their world and selectively sharing those with others who pass by. I'd have fun seeing someone else's pinned singularity next to the Washington monument, for instance. Or generally being able to play with gravity effects on light via AR.

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1. isoprophlex ◴[19 Nov 24 17:41 UTC] No.42186124[source]▶
Commenting to reinforce this idea: I'd love an AR approach where I can pin a black hole with a given radius into my living room, and walk around it!

The geosharing augmented reality thing mentioned by the parent comment is very very cool too, I'd pay a few bucks for that! Maybe make it social by letting black holes that people drop somewhere IRL merge, etc...

Reach out to me if you eventually would like to spin up a cheap bit of infrastructure to host the data of where people dropped their black holes, and need some help with that!

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2. mjrpes ◴[19 Nov 24 19:27 UTC] No.42187150[source]▶
It would be neat to also get stats about the black hole depending on where you are in relation to it (obviously this breaks physics as a micro black hole would immediately fall into the earth). Everything is based on the hawking radiation calculator: https://www.vttoth.com/CMS/physics-notes/311-hawking-radiati...

Example: Set mass of black hole to 1e12 metric tons, or about 100,000 great pyramids.

This has a schwarzschild radius of 1485 femtometers (1 femtometer is around size of a proton).

Nominal luminosity is 356 watts. You could power your computer! Lifetime is 1e12 gigayears.

An interesting thing comes with gravity. Gravity at the schwarzschild radius for this mass is 3e28 m/s^2, but this is at a smaller-than-an-atom radius.

If you put your hand within a foot of it, gravity would be 700,000 m/s^2.

You would need to be at a distance of 270ft to experience gravity from it that compares to earth (9.8 m/s^2).

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3. isoprophlex ◴[19 Nov 24 19:56 UTC] No.42187436[source]▶
That is 356 watts of luminosity from something so small?! Whoa! It says the peak of the radiation has an energy of 41 keV though, so better not look at it directly (:

I tried plugging in some other numbers and, at first confusingly, found that the luminosity goes up at lower masses?! But of course it radiates from it's outer shell, not the entire volume.

Wonderful tool, imagine playing with those parameters in AR

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4. lupsasca ◴[19 Nov 24 20:05 UTC] No.42187539{3}[source]▶
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!)
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5. mjrpes ◴[19 Nov 24 21:18 UTC] No.42188182{4}[source]▶
It's crazy how hot and luminous they get. At 45 seconds left in a black hole's life, it has the luminosity of 85,000 megatons of TNT, and only gets exponentially hotter as those 45 seconds count down. In the last fraction of a second of it's life, with one metric ton of mass left, its luminosity is greater than the sun.