Freak observers and the measure of the multiverse

TL;DR

The work tackles the measure problem in eternal inflation by separating equilibrium de Sitter fluctuations from non-equilibrium observer production. It reframes the pocket-based measure as $P_j=p_j f_j$, with $p_j$ enforcing equilibrium bubble abundances and $f_j$ weighting observers produced by non-equilibrium processes; crucially, it withdraws the contribution of freak observers by subtracting the equilibrium production rate $n_j^{(eq)}$ to form $\tilde{n}_j(\tau)$, ensuring a finite, well-defined measure. This yields vanishing weight for freaks (Boltzmann brains) even in an infinite, eternally inflating spacetime, while preserving the dominance of bio-friendly bubbles. The approach clarifies how to regulate infinities in the presence of both regular and freak observers, though it leaves open issues like bubble collisions and diffusion-based pocket formation for future work.

Abstract

I suggest that the factor $p_j$ in the pocket-based measure of the multiverse, $P_j=p_j f_j$, should be interpreted as accounting for equilibrium de Sitter vacuum fluctuations, while the selection factor $f_j$ accounts for the number of observers that were formed due to non-equilibrium processes resulting from such fluctuations. I show that this formulation does not suffer from the problem of freak observers (also known as Boltzmann brains).