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

(apps.apple.com)
313 points yunyu | 8 comments | 19 Nov 24 17:06 UTC | HN request time: 2.212s | source | bottom
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lupsasca ◴[19 Nov 24 17:07 UTC] No.42185680[source]▶
Hello! We are Dr. Roman Berens, Prof. Alex Lupsasca, and Trevor Gravely (PhD Candidate) and we are physicists working at Vanderbilt University. We are excited to share Black Hole Vision: https://apps.apple.com/us/app/black-hole-vision/id6737292448.

Black Hole Vision simulates the gravitational lensing effects of a black hole and applies these effects to the video feeds from an iPhone's cameras. The application implements the lensing equations derived from general relativity (see https://arxiv.org/abs/1910.12881 if you are interested in the details) to create a physically accurate effect.

The app can either put a black hole in front of the main camera to show your environment as lensed by a black hole, or it can be used in "selfie" mode with the black hole in front of the front-facing camera to show you a lensed version of yourself.

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1. jtbayly ◴[19 Nov 24 19:20 UTC] No.42187085[source]▶
I’m confused by what I see.

It looks like nothing actually disappears. I expected a black hole to not just affect what an area looked like, but also to “disappear” some part of what was there.

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2. useless_foghorn ◴[19 Nov 24 19:27 UTC] No.42187142[source]▶
I think that’s why this demonstration is interesting. It’s showing how the light can be bent around the black hole. Anything that crosses the event horizon won’t be coming back, but because of the lensing of the light you can “see” behind a black hole.
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3. jtbayly ◴[19 Nov 24 19:33 UTC] No.42187224[source]▶
So if I’m understanding correctly, the black hole is supposed to be between me and what I’m looking at, not in what I’m looking at?

If so, then my question is wouldn’t some light be lost to the black hole? Shouldn’t a substantial portion of the light coming at me from the other side of the black hole disappear into the black hole, making what does lens around dimmer?

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4. cft ◴[19 Nov 24 20:02 UTC] No.42187493[source]▶
Because, for an external observer, time infinitely slows down near the event horizon. In other words, during one hour by the clock of the far-away observer, the time that passes by the clock of the falling observer approaches zero as he approaches the event horizon. So, when you look from the outside, objects get 'frozen' as they approach the event horizon. For the falling observer, nothing special happens at the event horizon, and he just falls through.

If you happen to approach the event horizon closely and come back again far away to where you started, you will see that a lot of time passed at your origin, while by your clock, the trip might have been short.

5. bmurphy1976 ◴[19 Nov 24 20:47 UTC] No.42187922{3}[source]▶
Yes some light would be lost the black hole, but also some light you would not have normally seen is now coming your way due to space time warping.
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6. ayakang31415 ◴[19 Nov 24 21:29 UTC] No.42188284{3}[source]▶
Here's Veritasium video on Gravitational Lensing effect: https://www.youtube.com/watch?v=zUyH3XhpLTo
7. hunter2_ ◴[20 Nov 24 14:40 UTC] No.42194270{4}[source]▶
When you say "normally," do you mean all else being equal except no black hole? Or substitute an opaque mass for the black hole?
8. useless_foghorn ◴[20 Nov 24 19:47 UTC] No.42197423{3}[source]▶
A lot of light would be absorbed by the black hole. A lot of light paths would be bent and miss or nearly miss the black hole, making edges of the black hole quite bright. The dimming effect would be much larger than the (brighter) immediate periphery.