TAPIR Seminar

The quantum state of a universe dominated by vacuum energy has a nonzero temperature, much like that of a black hole. Under the right conditions, thermal fluctuations can lead to the appearance of freak, random observers, known as "Boltzmann Brains." The total number of observers in such a universe can easily be dominated by such fluctuations, rather than "ordinary observers" living in the warm aftermath of a Big Bang. I will discuss why such a situation should be considered as a severe problem for cosmological models, including standard LCDM, and also how it can be avoided, depending on details of the full quantum theory describing cosmological evolution.