Does string theory predict an open universe?

New paper! See here for related discussion.

The first two pragraphs:

If, as suggested by recent results [1], string theory exhibits a landscape of over 10^500 distinct, metastable vacua, its status as a conventional scientific theory is in jeopardy. Scientific theories must make predictions which are falsifiable by experiment. Such a large diversity of vacua means that essentially any low-energy physics might be realizable from string theory. Even ultra high-energy physics experiments may not yield additional information, since scattering at trans-Planckian energies leads to black holes [2] of ever increasing size, whose subsequent behavior (evaporation) is controlled by the low-energy physics of the ambient vacuum state. If recent results are any guide, string theory will be extremely difficult to falsify.

It is therefore important to carefully consider any robust implications of the string landscape. One of these, recently elaborated in [3], is the testable prediction that our universe must be open, with negative curvature. A recent analysis combining WMAP and Sloan Digital Sky Survey data gives Omega =1.003 +- 0.010 [4], but improved future observations could yield a statistically significant central value larger than unity, implying positive curvature. Would this rule out string theory?


hep-th/0610231
Authors: R. Buniy, S. Hsu, A. Zee

It has been claimed that the string landscape predicts an open universe, with negative curvature. The prediction is a consequence of a large number of metastable string vacua, and the properties of the Coleman--De Luccia instanton which describes vacuum tunneling. We examine the robustness of this claim, which is of particular importance since it seems to be string theory's sole claim to falsifiability. We find that, due to subleading tunneling processes, the prediction is sensitive to unknown properties of the landscape. Under plausible assumptions, universes like ours are as likely to be closed as open.