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

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

aplavin

Comments (67)

  • Waterluvian
    It’s fascinating how things that were inverted seem to become corrected when I point this at the pre-existing black hole in my room.
  • runtime_lens
    I wonder how much of that is scale rather than danger. Really large objects can feel unsettling even when you know they're harmless. VR seems especially good at triggering that response.
  • dluan
    I remember like 10 years ago when Occulus first came out there was that space simulation demo where you could go around the solar system in VR. You could also "fast travel" by zooming in towards a planet, moon, blackhole.Yeah, that was the day I learned I have a deep, crippling phobia of large objects. And Melanoheliophobia, which is fear of black holes. The only other time I've felt that way was snorkeling once near a giant 3 story tall bait ball of swirling fish, which was so disorienting and panic inducing that I vomited.
  • antonvs
    I tried this, and now my cat is missing!
  • 20k
    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 limitationsI wouldn't mind at all if it didn't say that this was a *physically accurate* black hole specifically, but this now falls under misleading science communication in a way that often gets hand waved away as if it doesn't matter, so we've got to clear some things up!1. The accretion disk shouldn't be red, people just expect it because it looks cool. Black hole accretion disks are near universally hot enough to be blue. Interstellar did this too, and tried to handwave it away very unconvincingly2. This is a non/low (?) spin black hole, which isn't super duper realistic3. It ignores the position of the camera (which affects the lorentz shifting)4. The doppler shifting isn't terribly accurate5. It doesn't model the accretion disk temperature distribution or colour with any kind of accuracy. Usually you model accretion disks as a blackbody radiator, shift it by the doppler, and to display this convolve this against the human eye response (LMS), go to XYZ, then RGB, do a physical tonemapping step, before an sRGB conversion. This instead does none of that - no step of this is done with any physical accuracy. Its not even illustratively correct as we'll get into6. The actual radiative transfer is very simplified compared to what you'd use for realsies, and isn't based on any real numbers, with very simplified equations. The opacity and emissivity of the disk is arbitrary, as is the size, and it does not correctly incorporate brightness or extinction, eg here https://github.com/aplavin/blackhole.plav.in/blob/2f004bfeca... is super simplified7. The wrong equation is used for the doppler calculation. They use the I^3 variant, whereas the data you get out of a disk sample is *radiant flux* which is actually F_obs = F_emit / (z+1)^4. This is a very common mistake in image processing, which means that the doppler shift and observer brightness isn't correct. Surface brightness over here https://github.com/aplavin/blackhole.plav.in/blob/2f004bfeca... is *not* a spectral radiance but instead a radiant fluxStuff like the brightness -> colouring conversion is particularly inaccurate. Eg if you check out the source:https://github.com/aplavin/blackhole.plav.in/blob/2f004bfeca...It maps the pseudo brightness completely arbitrarily to colour. The resulting colour/brightness here then doesn't correspond to anything remotely physical. It also performs a *linear* mapping of a linear quantity (brightness) to sRGB (which is a nonlinear process!!), which means that it doesn't even retain any of the underlying physical characteristics of the brightness simulation, which itself is quite inaccurate. Its vibes all the way downThis is all fine if you're doing visualisation, but this isn't an accurate simulation. I wish this was just called a visualisation of a black hole, but its being communicated as if this is super hard science with credentials and all
  • nomilk
    From a certain angle it looks like an eyeball https://imgur.com/a/Dam3XT0
  • csmoak
    Please correct me if I'm wrong, but it feels like the leading edge of the accretion disk (coming towards the viewer) should be significantly brighter than it is shown here, and the trailing edge (going away from) should be significantly dimmer?Or could the brightness shown be a result of it being Kerr vs Schwarzschild?
  • aizk
    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. 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.
  • hahahaa
    First time I have AR'd. That was cool. How does it keep the hole in the same point in space as I walk about?
  • drivingmenuts
    Good work! Gimmer two, chief!Two black holes at once?!?!?? Yeah, I'm crazy like that.
  • rgovostes
    See also: Black Hole Vision for iOS from Vanderbilt University. https://apps.apple.com/us/app/black-hole-vision/id6737292448
  • anon
    undefined
  • ninjahawk1
    Them: you can’t see what’s on the inside of a black holeMe: zooms in
  • anon
    undefined
  • charcircuit
    Wouldn't physically accurate turn your entire screen black? I would expect it to suck in way way more light than the example shows.
  • api
    The singularity is near.
  • ButlerianJihad
    "It really brings the room together" https://m.xkcd.com/1680/