Has any of these hypothetical theories a "higher" number of possible universes or has string theory landscape the same type of possible universes than brane cosmology?

  • $\begingroup$ from the armchair: i've always thought that "brane cosmology" is another title to Susskind's String Landscape cosmology. something like $10^{500}$ universes is what the say. $\endgroup$ – robert bristow-johnson Aug 16 '18 at 0:51
  • $\begingroup$ thank you for your answer. I asked this because in this question: physics.stackexchange.com/q/382035 (in the comments) it is said that they are not the sam (or that's what i interpreted). So I guess that this user was wrong, right? @robertbristow-johnson $\endgroup$ – user199226 Aug 16 '18 at 1:22
  • $\begingroup$ i dunno. i am an electrical engineer. my understanding is that "branes" come from membrane which is a generalization of string in string theory. many strings combine to become a membrane or a "brane". and M-theory is where branes come from or go to (even though the "M" was not specifically defined, many physicists think it stands for "membrane"). $\endgroup$ – robert bristow-johnson Aug 16 '18 at 1:55

Not all possible string vacua have branes in them. For example, heterotic string theories actually do not contain any D-branes at all. They do contain the NS5-brane, but that is not a brane on which open strings can end. Hence, not all string vacua can be brane cosmologies to begin with.

The set of brane cosmologies is the subset of the possible string vacua (so of the string landscape) in which there are large or even non-compact extra dimensions, while the four-dimensional universe familiar to us is attached to a D-brane. This is a funny scenario that could imply that there are other D-branes floating around, containing other universes that may or may not resemble our universe. I think it is somewhat more common for string model builders to assume that all the extra dimensions are small and that the universe is not confined to a D-brane, but the brane cosmology idea is (at present) certainly realistic enough to warrant serious attention.

  • $\begingroup$ And could brane universes change so much in nature that there could be brane universes behaving to other types of logic or even inconsistent universes? @StijnB. $\endgroup$ – user199226 Nov 17 '18 at 0:06
  • $\begingroup$ Conventionally, the other universes would be assumed to obey all the laws of string theory. You are free to invent some other theory about these other universes, but then it would be unclear what that theory should be, and it would be quite impossible to prove or disprove that theory, even more so than for string theory. It might be the case that the other universes have different matter content than ours, since the low-energy physics of string theory depends on many details that could easily vary. $\endgroup$ – Stijn B. Nov 17 '18 at 12:14

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