My top 10 string theory questions
Here are what I consider the top 10 questions in string theory*
(not necessarily in order of importance).
They are not the obvious questions, like,
"What is the value of this constant, and why?"
but questions so hard that they are usually ignored,
or even assumed to be already answered
(e.g., by adding "How.." to the beginning).
*For an alternative view, see
- Is spacetime four dimensional?
It sure looks that way. Also, 4 is the "critical" dimension of
quantum field theory.
- If not, does compactification work?
What forces the extra dimensions to hide, and
prevents them from reappearing?
Do the extra dimensions really do anything we
couldn't reproduce without them?
Does compactification destroy predictability?
- Does string theory work?
Perturbative finiteness seems to be the only reason for it,
but even in quantum field theory problems fixed at the
perturbative level are known to return nonperturbatively.
Is this what happens with the nonperturbative eleventh
dimension, which is described by nonrenormalizable
- If so, is a 10-dimensional perturbation expansion reasonable for
an 11-dimensional theory?
I'd like to see a 3-dimensional approach to 4-dimensional particle physics.
- Are there any other strings than the D=10(11) and 26 ones?
Dual theories only count once.
- Is supersymmetry useful?
Is fine tuning really that much worse than any other kind of tuning?
Are nonminimal Higgs's any worse than superpartners?
(Where are those Higgs anyway?)
- Is the graviton fundamental?
Oddly enough, it doesn't look that way in open string theory.
But if not there, maybe elsewhere...
- Do black holes exist?
We have evidence of gravitational fields strong enough to be
associated with black holes theoretically, but not of the event
horizons that define black holes.
- If so, what do you do with the singularities?
People worry about information loss from event horizons, but
doesn't a singularity signify breakdown of the theory?
- Does confinement work?
This is really a string theory question, since strings were originally
proposed to describe hadrons. By "work", I mean I want to actually
calculate the observed linear Regge trajectories that define the string,
not just some constants characterizing low-energy behavior (chiral
symmetry breaking, etc.), and see what happens to the bound states
as their excitation energy increases.