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On the dimensionality of spacetime (1997) [pdf]

by niklasbuschmann on 1/21/24, 4:59 PM with 52 comments

• by Jun8 on 1/21/24, 11:01 PM

  Some points you may find interesting:

  * If you're like me and are clueless about the terms "hyperbolic", "too simple" etc. used in the plot, take a lot at this SE answer that explains it (relatively) simply (https://physics.stackexchange.com/a/110880)

  * In his books the hard-SF writer Greg Egan has explored worlds with more than one timelike dimensions, see the discussion on HN ( https://news.ycombinator.com/item?id=36431620) and this comment on SE (https://physics.stackexchange.com/a/14106)

  * For very short distances space-time dimensions get reduced from four to two, see this post by Sabine Hossenfelder(http://backreaction.blogspot.com/2013/05/dimensional-reducti...)

• by dvh on 1/21/24, 6:00 PM

  Imagine what kind of computers could you make if you could radiate heat into more than one dimension. Or maybe you would get greedy and use up all available dimensions for interconnects and use one remaining dimension for heat dissipation anyway.

• by lopsotronic on 1/22/24, 1:29 AM

  My "cognitive white noise generator" has been locked on emergent spacetime for a decade now. The idea here, and I'm very loosely summarizing, is that the dimensions themselves are emergent properties of large scale entanglement - the mathematical "dimensions" resolve quite well into flesh and blood, "this is a chair" dimensions.

  The paper that sort of kicked it off

  https://arxiv.org/abs/1005.3035

  Quite evocative, but would require spectacularly sensitive testing apparatus to falsify . . and even then, other explanations aplenty.

  It is the fabric of space, after all, no shortage of theories.

• by emchammer on 1/21/24, 6:31 PM

  The chart on the second page of the article used to be located on a Wikipedia page called "Privileged character of 3+1 spacetime". I think it's curious that it seems to be mirrored over a diagonal axis.

• by anonymousiam on 1/21/24, 8:28 PM

  It seems that this paper assumes all the dimensions are flat. I believe that most current theories assume the higher dimensions are folded.

  https://en.wikipedia.org/wiki/Extra_dimensions

• by Sparkyte on 1/22/24, 6:17 AM

  I feel like we are over simplifying. This all rides on the existence of tachyon particles.

  Math used in certain ways can validate or simulate anything, but it doesn't mean a scenario of a dimension greater or smaller than ours exists except by theoretical representation. I am fine with that it is fun to think about.

  Dimensions beyond what we can perceive even if it is less than or greater than our own is pure nightmare fuel. I will simply leave it to math.

• by LASR on 1/21/24, 10:18 PM

  Nice analysis. But the point about stability - in other configurations of the universe, the subset of those that do evolve intelligence in some fashion is going to have different physics from our own.

  Stable intelligences might be another condition to explore in such an analysis.

• by bawana on 1/22/24, 12:52 PM

  As increasing dimensions adds to the possible arrangements of particles in a universe, then entropy has to be renormalized lower with every added dimension- more dimensions = more ways to achieve disorder.

• by balaise-rustine on 1/21/24, 7:06 PM

  Isn't 2+1 dimensions gravity a thing ? https://arxiv.org/abs/hep-th/9204099v3

• by qwerty456127 on 1/21/24, 6:18 PM

  I didn't read the paper yet, but the title reminds me of Robert Bartini who had a theory of time being 3-dimensional as well as space is.

• by epistasis on 1/22/24, 3:26 AM

  I am glad that I only encountered this after reading the book series that starts with the Three Body Problem.

• by KierPrev on 1/21/24, 7:21 PM

  Couldn't be other than Max Tegmark

• by thechao on 1/21/24, 9:00 PM

  My personal take is that 3+1 is not privileged; but that the physics that takes place in the other combinations is either so uninteresting it doesn't meaningfully interact, or that the number of Feynman paths through the non-3+1 cases all (mostly?) cancel out.

• by beefield on 1/22/24, 6:51 AM

  I have never quite understood why there can't be stable stallites in dimensions above 3.

  I mean, I know the argument that gravity inverse square law becomes inverse cube law in 4d, but what I do not understand is that what/why enforces that. Why in a hypothetical 4d world there just can not be a gravity-like force that is inverse square? Would that cause some kind of contradiction?