[HN Gopher] Show HN: Physically accurate black hole simulation u...
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Show HN: Physically accurate black hole simulation using your
iPhone camera
Author : yunyu
Score : 193 points
Date : 2024-11-19 17:06 UTC (5 hours ago)
(HTM) web link (apps.apple.com)
(TXT) w3m dump (apps.apple.com)
| lupsasca wrote:
| 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.
| lupsasca wrote:
| There are several additional options you can select when using
| the app. The first lensing option you can select is "Static
| black hole". In this mode, we simulate a non-rotating
| (Schwarzschild) black hole. There are two submodes that change
| the simulated field-of-view (FOV): "Realistic FOV" and "Full
| FOV". The realistic FOV mode takes into account the finite FOV
| of the iPhone cameras, leading to a multi-lobed dark patch in
| the center of the screen. This patch includes both the "black
| hole shadow" (light rays that end up falling into the black
| hole) and "blind spots" (directions that lie outside the FOV of
| both the front-and-rear-facing cameras). The full FOV mode acts
| as if the cameras have an infinite FOV such that they cover all
| angles. The result is a single, circular black hole shadow at
| the center of the screen.
|
| Next, you can select the "Kerr black hole" mode, which adds
| rotation (spin) to the black hole. Additionally, you can
| augment the rotational speed of the black hole (its spin,
| labeled "a" and given as a percentage of the maximal spin).
| lupsasca wrote:
| In a nutshell, the app computes a map from texture coordinate
| to texture coordinate. This map is itself stored as a texture
| --- to obtain the value of the map on texture coordinates
| (x,y), one samples the texture at (x,y) and the resulting
| float4 contains the outputs (x',y') as well as a status code.
|
| When the user selects the "Static black hole" mode, this
| texture is computed on the GPU and cached. The "Kerr black
| hole" textures, however, have been precomputed in
| Mathematica, due to the need for double precision floating
| point math, which is not natively available in Apple's Metal
| shading language.
|
| The source code, including the Mathematica notebook, can be
| found here https://github.com/graveltr/BlackHoleVision.
| lupsasca wrote:
| We hope you enjoy watching the world with Black Hole Vision
| and welcome any questions or feedback. If you like the app,
| please share it with your friends!
|
| The code was written at Vanderbilt University by Trevor
| Gravely with input from Dr. Roman Berens and Prof. Alex
| Lupsasca. This project was supported by CAREER award
| PHY-2340457 and grant AST-2307888 from the National Science
| Foundation.
|
| License: This app includes a port of the GNU Scientific
| Library's (GSL) implementation of Jacobi elliptic functions
| and the elliptic integrals to Metal. It is licensed under
| the GNU General Public License v3.0 (GPL-3.0). You can view
| the full license and obtain a copy of the source code at:
| https://github.com/graveltr/BlackHoleVision.
| timthorn wrote:
| By any chance, was Andrew Strominger involved in this at
| all? He gave the Andrew Chamblin Memorial Lecture in
| Cambridge last month and demoed something that looked
| similar.
| lupsasca wrote:
| 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.)
| lupsasca wrote:
| 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.
| jtbayly wrote:
| 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.
| useless_foghorn wrote:
| 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.
| jtbayly wrote:
| 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?
| bmurphy1976 wrote:
| 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.
| ayakang31415 wrote:
| Here's Veritasium video on Gravitational Lensing effect:
| https://www.youtube.com/watch?v=zUyH3XhpLTo
| cft wrote:
| 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.
| judge2020 wrote:
| I feel like this app could also be an app clip to make it so
| that you don't have to outright install the app to use it:
| https://developer.apple.com/app-clips/
| 20k wrote:
| As far as I can tell, the black hole's you're generating don't
| look especially correct in the preview: they should have a
| circular shadow like this https://i.imgur.com/zeShgrx.jpeg
| cybenko wrote:
| What happens with the rotating one and a realistic POV?
| graveltr wrote:
| It looks needlessly complicated and messy because the visually
| interesting region when rotation is turned on is blocked out by
| the FOV cutouts. We felt it was best to only allow the user to
| select the full FOV in this mode.
|
| Thanks for the question!
| lambdadelirium wrote:
| >physically accurate >event horizon doesn't appear in my room :(
| lupsasca wrote:
| Something to rejoice about, no? ;)
| bryant wrote:
| 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.
| lupsasca wrote:
| That's an excellent idea! And indeed, part of the reason we
| started with the iPhone is because we've been thinking from the
| get-go about an eventual extension to Apple Vision Pro. As I
| wrote in my other comment, this is part of an outreach effort
| to get the public (and students) excited about black hole
| physics, so we will always keep the code free and open source.
| isoprophlex wrote:
| 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!
| mjrpes wrote:
| 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).
| isoprophlex wrote:
| 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
| lupsasca wrote:
| 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!)
| mjrpes wrote:
| 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.
| deadbabe wrote:
| That's exactly what I thought this would be, imagine my
| disappointment.
| jerf wrote:
| You need a full 3D scan of the environment of everything the
| black hole can "see" from the position you want to put it in,
| not just the traditional "augmented reality" that sits on top
| of a current camera feed, because black holes are also
| essentially 360 degree cameras that from some angle will let
| you see anything around them. Not impossible, but harder than
| "just" taking an augmented reality feed.
| grahamj wrote:
| It could be done in VR instead, where the entire environment
| is available.
| dartos wrote:
| Not everything needs to generate cash :)
| ripped_britches wrote:
| Generating cash is a proxy for generating long term human
| value
| tjohns wrote:
| Not everything needs to generate long term human value.
| It's okay to just have fun, too.
| syndicatedjelly wrote:
| What a warped thing to believe in
| robocat wrote:
| Under what assumptions?
|
| Just trying to guess at what they could be is costing me
| random time...
| 01HNNWZ0MV43FF wrote:
| Does it use iPhone-specific features or could it work on, e.g., a
| desktop
| lupsasca wrote:
| We wanted the app to work on an iPhone and that required the
| use of Apple Metal code. This could of course be ported to a
| desktop but we're not sure there would be much interest in
| that?
| lagrange77 wrote:
| Maybe WebGPU would be a good porting target.
|
| Really cool app btw!
|
| I have once seen a video of Kip Thorne, explaining that the
| black hole visual effects of Interstellar were an actual
| physical simulation. I wouldn't have thought, that it was
| feasible to run on an iPhone.
| lupsasca wrote:
| 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.
| lagrange77 wrote:
| Cool, thanks for the reference!
| jtbayly wrote:
| I was able to install it on my M1 Mac, fwiw.
| Y_Y wrote:
| This is not a simulation of a black hole, but rather an image
| filter that emulates one particular effect.
| lupsasca wrote:
| Yes, agreed. We thought it would be fair to call it a
| "simulation" of what your surroundings would look like if a
| black hole were within your FOV, but as you say we do not take
| into account all effects (time delays in particular would
| require a lot of buffering and we decided this would be
| impractical to implement, and not that illuminating).
| hnuser123456 wrote:
| This is still nice when there are so many artistic images of
| black holes that do not take such care to use known physics
| to create an accurate image. Well done all. Looking forward
| to seeing what BHEX sees.
| lupsasca wrote:
| 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...
| hnuser123456 wrote:
| Read all of it, only question I have is... napkin math,
| how much more resolution over EHT alone?
| Y_Y wrote:
| You're right that the time delays and redshifting wouldn't
| add much to a toy app, but some of us are here for the
| physics.
|
| Honestly it's not so far-fetched (to me) that in a few years
| someone will have GRRMHD simulations running in real time on
| a portable device.
|
| Are you familiar with A Slower Speed of Light? It's a game
| which has some nice special-relativistic effects.
|
| http://gamelab.mit.edu/games/a-slower-speed-of-light/
| lupsasca wrote:
| 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.
| Y_Y wrote:
| That's awesome. It's extra crucial to have engaging
| outreach when your research is so far from application.
| There's so much scope for wowing people with astro and if
| you can enrich our culture and justify funding at the
| same time that's a win-win.
|
| (Just for clarity the second R in GRRMHD is for
| radiation. I know it's typical to just push some photons
| through the GRMHD results to produce renders, bit since
| I'm dreaming let's treat the radiation self-
| consistently.)
| mock-possum wrote:
| Does anyone else find it jarring to unexpectedly be shown the
| selfie camera view? Showing both camera feed thumbnails
| constantly while using this app is a little odd.
|
| Still, kinda fun, reminds me of playing around with different
| blur / liquidify filters in photoshop back in the day.
| graveltr wrote:
| Good point. In a future update, we can add a button to show /
| hide the camera views.
| spaceisballer wrote:
| Just tried to check it out. First boot it crashed, killed app and
| tried again and now it won't open. I'll try and reinstall and do
| over. iPhone 16 Pro, iOS 18.1
|
| Quick edit- I did exactly that and now it works fine. First boot
| up before seemed like it got stuck when asking for permission to
| use the camera.
| lupsasca wrote:
| 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?
| blululu wrote:
| This is awesome. I see that this is GPL and open on GitHub. Thank
| you for sharing. If you are open to feature requests that I am
| too lazy and stupid to accomplish on my own, I would appreciate
| the option to drop the multi camera view and the option to
| capture a photo. Also plus one to the idea of being able to pin
| the black hold to a specific orientation so you can see what it
| looks like to pan around an object adjacent to the black hole.
| lupsasca wrote:
| 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...
| xqcgrek2 wrote:
| As always, wonder what a particular "free" thing is selling and
| to whom. In this case it's something called BHEX, to NASA.
| lupsasca wrote:
| 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.
| consumer451 wrote:
| First thing I wondered is what would happen if I pointed it
| another screen, with an image like this loaded. I realize that
| it's not realistic due to the z-axis, and field of view, but it's
| pretty fun.
|
| https://esahubble.org/images/heic0609a/
| insamniac wrote:
| As above so below. I love how it looks so similar to a
| colonoscopy.
| lupsasca wrote:
| There are other apps out there for this kind of black hole
| vision...
| beretguy wrote:
| Dude, I like your comments.
| floxy wrote:
| Would a person notice red-shifts from the black hole as well?
| lupsasca wrote:
| 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.
| floxy wrote:
| Since you don't notice any red-shift with your eyes in daily
| life, why is zero velocity relative to the camera not a
| natural choice? Or maybe I'm not following you?
| bossyTeacher wrote:
| Pendatic but can I ask why does this app require 17.5 or later?
| For reference, the latest iOs version is 18. What specific API is
| being used to require that version?
| graveltr wrote:
| Good point, the minimum version should be an earlier version of
| iOS, we don't use any APIs that are only available in 17.5 or
| later.
|
| Thanks for pointing that out.
| CuriousSkeptic wrote:
| Glad to hear, blocked install for me, so a bit more than
| pedantic :)
| gigatexal wrote:
| Instant download for me. I'm a sucker for anything black hole
| related.
| lupsasca wrote:
| 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/
| gigatexal wrote:
| I had no idea! Thank you!!
| majgr wrote:
| Is in the middle of black hole zero gravity? Then, is there
| another event horizon somewhere inside black hole?
| alex_suzuki wrote:
| I don't think anybody really knows what's inside a black hole.
| That's kind of their defining property.
| grahamj wrote:
| Of course we do - everything that fell in but wasn't radiated
| out ;)
| seanw444 wrote:
| Well technically it approaches infinite gravity. It's a
| gravitational asymptote. But like the other commenter said, no
| way to know what it actually is in reality, as we only have
| mathematical concepts that may or may not match reality.
| codethief wrote:
| Very nice - if only I could try it! :'-) Any chance this could be
| ported to Android, at least for high-end devices with a decent
| GPU?
| neallindsay wrote:
| Another nice feature would be if it could simulate an accretion
| disk.
| aljgz wrote:
| No plans for an Android version?
| elashri wrote:
| That seems cool. It would be interested to see a simulation for
| Kerr-Newman BH. Although I have no idea what would be the best
| way to see the effects without some sort of perturbation. Not
| that this is astrophysical BH of course. Just a thought
| experiment.
| ilrwbwrkhv wrote:
| Oh man this so reminds me of the old iPhone apps which were so
| epic and so cool
| ale42 wrote:
| Did anybody else first think --before seeing the app images--
| that it was somehow using the camera of the iPhone to simulate
| the physics of the black hole?
| pokstad wrote:
| It does
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