Does string theory predict an open universe?

TL;DR

This paper critically examines the claim that string theory predicts an open universe, finding that due to unknown landscape properties, the universe's curvature could be open or closed with similar likelihoods.

Contribution

It analyzes the robustness of the string landscape's prediction of an open universe, highlighting the impact of subleading tunneling processes and landscape uncertainties.

Findings

Prediction is sensitive to unknown landscape properties

Universes like ours could be closed or open with similar probability

Subleading tunneling processes affect curvature predictions

Abstract

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 one of string theory's few claims 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.