A burning question in theoretical physics these days is that of whether Boltzmann Brains dominate the string theory anthropic landscape. It seems that to answer this question one must study the details of how BBs nucleate and how string vacua decay. String vacua can do pretty much anything, so attention is focused on the detailed study of how to make the Brains and ad hoc choices of “measure” on the multiverse, with these issues occupying the attention of many leading figures in cosmology. While the question of BB domination of the multiverse remains open, it is becoming increasingly clear that BBs may soon dominate hep-th. Their nucleation rate is increasing, while the decay rate of the rest of the field also appears to be increasing. Doing phenomenology and extrapolating data a few years into the future, Boltzmann Brain domination of hep-th appears inevitable.
The latest hep-th arXiv postings include two new contributions to BB studies. One is from a group of three physicists at Berkeley, the second is from a large collaboration of six cosmologists on both coasts, including three of the major figures in the subject. For a third, more intellectually substantive, contribution of similar length, there’s a new posting on the subject from Lubos.