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Gravity seems holographic. What does that mean for reality?

300 points · 234 comments · ibobev

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. peter_d_sherman · 1790408570 · focus · HN ↗
  >"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."
  Space filling curves with three dimensions could potentially provide us with some clues:
  <a href="https://en.wikipedia.org/wiki/Z-order_curve" rel="nofollow">https://en.wikipedia.org/wiki/Z-order_curve
  "In mathematical analysis and computer science, functions which are Z-order, Lebesgue curve, Morton space-filling curve,[1] Morton order or Morton code map multidimensional data to one dimension while preserving locality of the data points (two points close together in multidimensions with high probability lie also close together in Morton order)."
  Also, to answer the question, potentially Octrees might be interesting to research:
  <a href="https://mathworld.wolfram.com/Octree.html" rel="nofollow">https://mathworld.wolfram.com/Octree.html
  "An octree is a rooted tree that represents a three-dimensional region by recursively subdividing it into eight congruent, axis-aligned cuboids, usually cubes (Meagher 1982, Samet 1990). Each internal node represents a spatial cell and has eight children, one for each octant of the cell. A tree leaf represents a cell that is not subdivided further."
  But, since "a picture is worth one thousand words":
  <a href="https://www.google.com/search?q=octree&udm=2" rel="nofollow">https://www.google.com/search?q=octree&udm=2
  Another thing to consider is that according to the Knuth Transform (aka Left-Child Right-Sibling (LCRS) representation), apparently any k-ary tree (Octree = 8-ary tree) can apparently be converted into a Binary Tree without losing information:
  <a href="https://en.wikipedia.org/wiki/Left-child_right-sibling_binary_tree" rel="nofollow">https://en.wikipedia.org/wiki/Left-child_right-sibling_binar...
  So, is there a 1D (or 2D) representation for 3D reality?
  Well, I personally don't know!
  What I do know is that a certain popular rock group sang the following lyric in one of their popular rock songs, back in 1999:
  "Space may be the final frontier -- but it's made in a Hollywood basement..."
  -The Red Hot Chili Peppers, "Californication"
  So, you decide! :-)

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