Sinks in the Landscape and the Invasion of Boltzmann Brains

This paper extends the recent investigation of the string theory landscape [1], where it was found that the decay rate of dS vacua to a collapsing space with a negative vacuum energy can be quite large. The parts of space that experience a decay to a collapsing space, or to a Minkowski vacuum, never return back to dS space. The channels of irreversible vacuum decay serve as sinks for the probability flow. The existence of such sinks is a distinguishing feature of the string theory landscape. We describe relations between several different probability measures for eternal inflation taking into account the existence of the sinks. The local (comoving) description of the inflationary multiverse suffers from the so-called “Boltzmann brain” problem unless the probability of the decay to the sinks is sufficiently large. We show that some versions of the global (volume-weighted) description do not have this problem even if one ignores the existence of the sinks. Finally, we describe a simplified approach to the calculations of anthropic probabilities in the landscape, which is less powerful but also less ambiguous than other methods. To the memory of Eugine Feinberg, who was trying to make a bridge between science, philosophy and art.