The dangerous irrelevance of string theory
  We comment on the relation between string theory and empirical science,
grounding our discussion in cosmology, a subject with increasingly precise data
in which this connection operates at several levels. It is important to take
into account the phenomenon of dangerous irrelevance: over long times or large
field ranges, physics can become sensitive to higher scales than the input
energies. This pertains in inflationary cosmology (and possibly other aspects
of horizon physics). String theory also contributes to our understanding of
observational constraints and search strategies at the level of low energy
field theory. We illustrate this with a current example concerning a new form
of non-Gaussianity generated by very massive degrees of freedom coupling to the
inflaton. New constraints on such fields and couplings can be obtained from
existing data, increasing our empirical knowledge of the universe. This builds
in part from the development of the string landscape, which is neither random
nor an abdication of science as has sometimes been suggested. {\it Invited
contribution to the proceedings of the conference `Why trust a theory'.}
