Thread

Gravity seems holographic. What does that mean for reality?

300 points · 234 comments · ibobev

VyseofArcadia · 1790359458 · focus · HN ↗
Mathematician, not physicist, but it seems reasonable to me that you could encode a sufficiently constrained 3D space on a 2D boundary. And if you have such an encoding, it also doesn't seem insane that some things might be more easily modeled on the 2D boundary than the 3D space.
If you can convert back and forth between a 2D representation and a 3D representation, and different phenomena are more easily modeled in each, does it matter which is "real"? Unless of course you can come up with a specific prediction and experiment to test it.
1. wormius · 1790362243 · focus · HN ↗
  Yeah, there's a great talk about the physics of the holographic information encoded on the surface by Raphael Bousso (if you have an hour):
  <a href="https://www.youtube.com/watch?v=GHgi6E1ECgo" rel="nofollow">https://www.youtube.com/watch?v=GHgi6E1ECgo
  HIGHLY recommend it for lay folks interested in this stuff. Which reminds me, I should yt-dl this so it's not lost, and I have a copy...
  1. LargoLasskhyfv · 1790374172 · focus · HN ↗
    In 240p only? :-(
    einsteinx2 · 1790374868 · focus · HN ↗
    The YouTube video was uploaded 18 years ago, and looks like it was filmed on a VHS camcorder. I guess it could have been 480p as the original would have been 480i, but it wouldn’t look all that much better.
    ronsor · 1790377485 · focus · HN ↗
    VHS has an effective resolution of ~240p anyway.
    rightnutwingjob · 1790377145 · focus · HN ↗
    How much more knowledge are you hoping to extract from a 4K version?
    gigatexal · 1790381469 · focus · HN ↗
    There’s some physics-y Shannon entropy data or black hole joke in there somewhere I just am not mart enough to find it.
    LargoLasskhyfv · 1790381844 · focus · HN ↗
    I haven't watched it so far, but I'd expect some diagrams on a chalk-, or whiteboard, maybe some 'overhead' projection. These will all be almost unrecognizable at that resolution, on current screens. Would have to try to upscale with AI. Which I won't.
    rkagerer · 1790386398 · focus · HN ↗
    I watched the whole thing, I didn't notice anything substantial lost.
  2. mito88 · 1790378708 · focus · HN ↗
    what app do you use for yt-dl?
    jacobolus · 1790382466 · focus · HN ↗
    <a href="https://github.com/yt-dlp/yt-dlp" rel="nofollow">https://github.com/yt-dlp/yt-dlp seems to be a more currently maintained fork of the original <a href="https://github.com/ytdl-org/youtube-dl/" rel="nofollow">https://github.com/ytdl-org/youtube-dl/
    analog8374 · 1790438970 · focus · HN ↗
    can concur
    int_19h · 1790382599 · focus · HN ↗
    <a href="https://github.com/yt-dlp/yt-dlp" rel="nofollow">https://github.com/yt-dlp/yt-dlp is generally where the most up-to-date workarounds for Google's attempts to block downloads are.
  3. rkagerer · 1790385379 · focus · HN ↗
    This is a great video, thanks for sharing.
    My favorite quote and a point where something really clicked was when he said "If you tried smaller you would instead be making a Planck-size black hole".
2. senderista · 1790382997 · focus · HN ↗
  Is the physical nonlocality of the relationship between the bulk and boundary somehow related to the noncontinuity of any bijection between manifolds of different dimension?
3. GoblinSlayer · 1790411310 · focus · HN ↗
  It's Cauchy problem.
4. bmacho · 1790413501 · focus · HN ↗
  > Mathematician, not physicist, but it seems reasonable to me that you could encode a sufficiently constrained 3D space on a 2D boundary. And if you have such an encoding, it also doesn't seem insane that some things might be more easily modeled on the 2D boundary than the 3D space.
  Yes, you are missing the point entirely. Merely saying "you could encode a sufficiently constrained 3D space on a 2D boundary" as you correctly noticed, would be meaningless.
  The observation is that the 3D space has properties that are weird in 3D but natural in its 2D representation.
  > does it matter which is "real"?
  No.
  Also if you have different representations of something and your job/goal is to think and gain instinct then you should keep in mind all the representations, they very likely will be useful. (An observed property of mathematics is that if a mathematician pours 40 hours per week of work in an area for years in a topic other mathematicians haven't exhausted yet, she will find something there.)

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