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String theory has a landscape of possible universes. Brane cosmology is related to string theory because it needs extra dimensions, but are the possible different universes of brane cosmology embedded in string theory landscape? Are they part of it?

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

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

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These are two different things.

The string theory landscape is the collection of all possible vacua. Polchinski in String Theory, Vol I, writes:

The main problem is that whilst there is a unique theory there are an enormous number of classical soultions ... upon quantisation each of these is a possible ground state, ie vacuum, for the theory and the physics is different in each.

DBranes are extended objects on which open strings can end. They range from D(-1), an instanton, D0 a D-particle to D25 a space filling brane. A stack of branes induces a gauge theory and these are then used to build the standard model of particle physics.

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  • $\begingroup$ So the brane cosmology model "landscape" has infinitely many possible universes with even different fundamental laws of physics I suppose. If they have different landscapes how is it that brane cosmology "comes" from string theory? @MoziburUllah $\endgroup$ – user179736 Jan 24 '18 at 23:44
  • $\begingroup$ @NieinOfinfo: good question - the honest answer is that I don't know. I do know that this is what is called string phenomenology where they try to get contact with the standard model. They've been able to construct the gross structure but not the fine detail. $\endgroup$ – Mozibur Ullah Jan 24 '18 at 23:52
  • $\begingroup$ Ok. So infinitely many brane universes (each one with fundamental different physica laws) could exist isn't it? (Like Max Tegmark mathematical universe hypothesis where all these universes have different fundamental physical laws and structure en.wikipedia.org/wiki/Mathematical_universe_hypothesis). But if this is right, would all brane universes have strings? (If laws change, there could be universes where strings could not exist) @MoziburUllah $\endgroup$ – user179736 Jan 25 '18 at 11:38
  • $\begingroup$ @nieinOfinfo: I think so. But surely the point of physical modelling is to build a model that looks like ours? It seems a little odd to say that simply because a model can be built in string theory then must model must exist. $\endgroup$ – Mozibur Ullah Jan 25 '18 at 13:03
  • $\begingroup$ of course this is all speculation. So with "i think so" do you mean that these universes would all have strings on them? If yes, then If laws of physics changed, wouldn't that mean that in some brane universe there would be laws of physics inconsistent with string theory? Or is string theory a fundamental requirement for brane cosmology? (despite fundamental laws could change, there couldn't be any universe without strings, because without them brane universes could not exist?) @MoziburUllah $\endgroup$ – user179736 Jan 26 '18 at 12:29

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