  The standard $\Lambda$CDM model provides an excellent fit to current
cosmological observations but suffers from a potentially serious Boltzmann
Brain problem. If the universe enters a de Sitter vacuum phase that is truly
eternal, there will be a finite temperature in empty space and corresponding
thermal fluctuations. Among these fluctuations will be intelligent observers,
as well as configurations that reproduce any local region of the current
universe to arbitrary precision. We discuss the possibility that the escape
from this unacceptable situation may be found in known physics: vacuum
instability induced by the Higgs field. Avoiding Boltzmann Brains in a
measure-independent way requires a decay timescale of order the current age of
the universe, which can be achieved if the top quark pole mass is approximately
178 GeV. Otherwise we must invoke new physics or a particular cosmological
measure before we can consider $\Lambda$CDM to be an empirical success.
