Thread

1. anigbrowl · 1790380260 · focus · HN ↗

   Pause for a moment to reflect on how outrageous this assertion is. You can’t see into the box at all. Nevertheless, holography says that you can learn exactly what’s happening everywhere in the box without any access to the interior. Observing the surface alone is enough. In this sense, the amount of stuff that fills a box is the same as the amount of paint that covers it. That’s a violation of logic and geometry.

   The breathless tone of this article obscures rather than illuminates its subject. It sounds as if the author describes a box with some particles bouncing around inside, and every time a particle bounces off the wall of the box the outside glows briefly indicating the location and intensity of the collision. The author is amazed that by repeatedly measuring this, you can draw inferences about what's going on in the box.

   I can't see what's 'outrageous' about this. You need a lower surface which registers information about activity inside a higher-dimensional volume, some way to accurately read that information, and the time/patience to repeat the measurement many times. Isn't this how radar works, or feeling your way around a pitch-dark room using only the 2-dimensional surface of your hands (or shins)? We know from computer science that you can mathematically encode any structure of arbitrary dimension into a binary tree. One might as well ask how it's possible that our complex 3 dimensional world can be contained in the flat surface of a mirror, film strip, or camera sensor.

   1. pimlottc · 1790381917 · focus · HN ↗

      It’s not just drawing inferences, though; it’s saying you can determine exactly what’s happening in the box. But the pigeonhole principle would suggest there’s far more possible states in the 3-dimension volume than can be unique expressed on the 2-dimensional surface. That’s the part that defies common sense.

      1. ReflectedImage · 1790383246 · focus · HN ↗

         A 3d volume can contain a number of states equal to it's 2d dimensional surface.

         All the extra states you would assume the 3d volume can contain are actually a single state called Black Hole.

         There is a limit to how much you can fill a 3d volume before it's a Black Hole basically.

         1. thaumasiotes · 1790435538 · focus · HN ↗

            > All the extra states you would assume the 3d volume can contain are actually a single state called Black Hole.

            How can that be? Don't different black holes have different masses?

            1. ReflectedImage · 1790456351 · focus · HN ↗

               Well the density goes down the larger the black hole so the extra states are still missing.

               For exactly how that works, I'm a Comp Sci not a Physicist.

               1. thaumasiotes · 1790551292 · focus · HN ↗

                  > Well the density goes down the larger the black hole so the extra states are still missing.

                  Huh? If the correlation between density and mass is perfect, that means two things:

                  1. There is an upper limit on the mass of the black hole, set by the volume of the box containing it.

                  2. The black hole's possible mass and density occupy a one-dimensional space and not a two-dimensional space.

                  Now, it appears to be true that the (possibly nonlinear) correlation between mass and density is perfect; for any mass a black hole can have only one density. But that doesn't make the space of possibilities finite. It certainly won't make it into a single point. And in fact black holes appear to have three independent physical dimensions: their mass, their electric charge, and their spin.

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