Big questions in M-theory

Recently there has been a lot of discussion about questions in physics and mathematics that we should confront in the new millenium; see The top 10 physics problems for the next millenium and The Clay Mathematics Institute millenium prize problems. In this spirit, and to stimulate discussion, I've begun collecting outstanding questions in M-theory.  Please submit your favorite question to; questions added will be credited.


Fundamental principles

What are the fundamental degrees of freedom of M-theory?
(Does this question apply, or is it time to abandon the reductionist paradigm?)
What are the dynamical laws governing their interaction?

What are the observables of M-theory? (R. Bousso)

Is M-theory holographic?
Does this explain the smallness of the cosmological constant?
How does one understand the emergence and breakdown of (semi-)classical spacetime (and in particular, its causal structure) from M-theory (or, if appropriate, from a more fundamental theory of quantum gravity)? (V. Hubeny)

Can we recover approximately local M/string theory from the AdS/CFT correspondence?

What is the role of supersymmetry in M theory:  it seems intrinsic at high energies; especially at low energies is it a theoretical crutch or a fundamental principle or something in between? (E. Silverstein)

Vacua, backgrounds, and phenomenology

Why are there three light generations and four astronomically large dimensions; are these just accidents? (E. Silverstein)

Should we expect low-energy particle physics to arise from a generic compactification, or is the very constraining data on the cosmological term pointing us toward some very specific backgrounds of M theory? (E. Silverstein)

Can we obtain de Sitter space as a solution to M-theory?

Is the Hilbert space of spacetimes with positive cosmological constant finite-dimensional? (R. Bousso)

Can string theory be discretized in the following sense:  Is there a sequence of theories with finite-dimensional Hilbert spaces, such that string theory emerges in the infinite-dimensional limit? (R. Bousso)
How can we calculate the quantum mechanical effects of heavy objects like black holes and their effects if any on long-distance quantities like the cosmological constant?  (E. Silverstein)
To what extent are different M theory backgrounds connected, whether on or off the moduli space, and what does this imply for attempts at background-independent formulations of the theory? (E. Silverstein)
What is the role of noncritical string theory backgrounds:  are such backgrounds generically connected to critical string theory backgrounds via tachyon condensation? (E. Silverstein)
Is it possible to find M-theory vacua generating hierarchies in novel ways (e.g. through large redshifts)?
Are there realistic scenarios for phenomenology with the true string scale far below the apparent Planck scale?
Would such scenarios enable one to experimentally study black hole dynamics?
How do we treat RR backgrounds in string theory?


Black holes

If M-theory is holographic,  is that the resolution of the black hole information paradox?
Where does Hawking's calculation fail?
Can we reconcile the observations of observers inside and outside a black hole horizon?
Can we compute the entropy of all black holes (including Schwarzschild)  exactly? (G. Horowitz)
How can we understand the universality of black hole entropy (the fact that it is always A/4 for all types of charges)?  (G. Horowitz)
Are the singularities of gravitational collapse and cosmology resolved in M-theory? (G. Horowitz)

Other issues

Is QCD proper (without extra degrees of freedom, i.e. not "MQCD" or SQCD) a string theory?  If so how is this consistent with Kutasov/Seiberg? (E. Silverstein)