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As it is, what is currently and seemingly incomplete in M-theory? One example I can give is explaining dark matter proportions and.. how do we perceive the world as 4-dimensional.

Thanks everyone.

user27515
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2 Answers2

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A major list of incomplete things in M-theory (I will ignore those that are not M-theory specific, which you can find in generic string theory questions):

  • 2-brane constructions--- if you make a 2-brane stack, this is described by Schwarz Chern-Simons theory, under certain conditions. Making the general AdS/CFT correspondence for the 2-brane case is important, and I believe still unsolved.
  • 5-brane constructions--- what is the AdS/CFT for five-branes? We don't know as far as I know.
  • What are the complete orbifold types for M-theory--- for strings, the orbifolding was understood from wordsheet considerations, but in M-theory, the Horava-Witten domain wall was understood from anomaly cancellation and needing to incorporate heterotic strings. Are these constructions fully consistent in M-theory (beyond string theory) (I am certain that yes)? What other orbifolded theories have we missed?
  • What is the relation between orbifolds and branes? Can one resolve orbifolds into combinations of matter branes?
  • What are orbifold dynamics--- they don't jiggle like normal gravitational things.
  • At what dimension does maximal supergravity stop being renormalizable?
  • Is there a complete intrinsic description of M-theory which is not based on a IIA theory compactification (Matrix theory), or on a near-2brane or near-5brane description?

I don't know if all of these are still active, or still unsolved, but these are the things that worry me when I think about M-theory personally. There is another thing that is not M-theory specific, but where I think M-theory methods are most promising:

  • What are black hole emissions--- unitarity demands that what information goes in to a black hole comes out. What comes out of black holes? Is it always thermal? I believe not, and the issue will be resolved soon.
Ron Maimon
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One basic thing that's incomplete about M-Theory is that the theory isn't even completely defined. One can talk about M-Theory in certain limits where it reduces to string theory, or one can talk about the low energy (non-quantum) supergravity theory which M-Theory reduces to, but there is no definition of what M-Theory actually is as a quantum theory in 11 non-compact dimensions. In particular, the full quantum mechanical lagrangian for M2 branes is not known, although classical limits may be deduced.

user8260
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