4 ms·

I'm familiar with the idea of coordinate transforms and projections, so I get the idea that you could project our 3D universe onto a 2D surface, and I kind of s

by PaulAJ 10y ago

I'm familiar with the idea of coordinate transforms and projections, so I get the idea that you could project our 3D universe onto a 2D surface, and I kind of see how a hologram encodes 3D information, but I don't see how that is a useful idea. Or are there only certain kinds of 4D information that can be encoded in the 2D surface, so our 4D model of space and time gets reduced to a theory of only 2 dimensions? Are there conceivable arrangements of a 4D universe that can't be represented in this way?

marcosdumay 10y ago
Laymen "easy" language makes everything harder to understand. The holographic principle means that if you take a sphere somewhere, the amount of entropy you can push there grows with r^2, and not with r^3 like you'd expect.
- bsaul 10y ago
  Thanks a lot. I've just watched susskind talk on the universe as a hologram ( https://youtu.be/2DIl3Hfh9tY https://youtu.be/2DIl3Hfh9tY ), and it didn't occured to me until i read what you just said simply that the holographic principle meant you could actually push less stuff / bits in a black hole by growing it, than you first thought if you compared it to a volume growing. So that meant information was stored on its surface (r^2), and not inside it (r^3). Am i correct ?
  - marcosdumay 10y ago
    Keep in mind that IANAP. The information stored is proportional to the surface, not volume. But also, the holographic principle applies to more than black holes. At any volume, the maximum information you can put there is proportional to r^2. That applies to all the volumes inside the volume you just measured... what means that a volume can not be completely full (a weird case of apparent non-locality). An hologram is a better analogue to it than information being stored on the surface because, outside of black holes it apparently isn't all on the surface. (I guess for the black hole information loss problem, information being in the surface or in a hologram don't make much difference.)
VLM 10y ago
Having only read the abstract (so I might have it totally wrong) we have the 2D holographic picture from the cosmic microwave background already and we're trying to fit that data to various theories. The cool kid theory used to revolve around dark matter in some way I'm a little unclear on. If you run a bunch of simulations on imaginary 4D universes playing games with the usual cosmological parameters, sometimes with some parameter settings processing the results as a holographic projection gives better match to the pix we already have, than stuff done that relies on dark matter and things. Quantum field theory mixes into this which is interesting because that usually applies to little things not the shape of the universe size stuff. I'm working on an automobile analogy but its not easy.

by PaulAJ 10y ago

marcosdumay 10y ago

Laymen "easy" language makes everything harder to understand. The holographic principle means that if you take a sphere somewhere, the amount of entropy you can push there grows with r^2, and not with r^3 like you'd expect.

bsaul 10y ago
Thanks a lot. I've just watched susskind talk on the universe as a hologram ( https://youtu.be/2DIl3Hfh9tY https://youtu.be/2DIl3Hfh9tY ), and it didn't occured to me until i read what you just said simply that the holographic principle meant you could actually push less stuff / bits in a black hole by growing it, than you first thought if you compared it to a volume growing. So that meant information was stored on its surface (r^2), and not inside it (r^3). Am i correct ?
- marcosdumay 10y ago
  Keep in mind that IANAP. The information stored is proportional to the surface, not volume. But also, the holographic principle applies to more than black holes. At any volume, the maximum information you can put there is proportional to r^2. That applies to all the volumes inside the volume you just measured... what means that a volume can not be completely full (a weird case of apparent non-locality). An hologram is a better analogue to it than information being stored on the surface because, outside of black holes it apparently isn't all on the surface. (I guess for the black hole information loss problem, information being in the surface or in a hologram don't make much difference.)

VLM 10y ago

Having only read the abstract (so I might have it totally wrong) we have the 2D holographic picture from the cosmic microwave background already and we're trying to fit that data to various theories. The cool kid theory used to revolve around dark matter in some way I'm a little unclear on. If you run a bunch of simulations on imaginary 4D universes playing games with the usual cosmological parameters, sometimes with some parameter settings processing the results as a holographic projection gives better match to the pix we already have, than stuff done that relies on dark matter and things. Quantum field theory mixes into this which is interesting because that usually applies to little things not the shape of the universe size stuff. I'm working on an automobile analogy but its not easy.