Quantum Cyclic Cosmology with Sean Carroll

The loophole is if you have integers rather than irrational numbers , you can avoid Boltzman brains by making everything happen much more quickly . The consequence of that is you have to live with an exact repeat of the universe an infinite number of times in the past and future . The philosopher Friedri Nature imagined that time and everything within it might repeat eternally into both the future and the past . It's an idea we explored in our book battle of the big bang . But now there's a new paper that suggests that exact cosmic repetition could be realized within quantum mechanics and might offer a way around one of cosmology's strangest problems, the threat of boltsman brains . So to help us unpack this, I'm super excited by the fact I'm joined by the papers lead author Sha Carol . Welcome Shan. How are you doing ? Great. Thanks very much for having me here, Phil . Yeah, I'm super excited about this . Let's begin with the mystery of the the big bang's low entropy condition . If if entropy has been increasing like for the past 14 billion years , wouldn't we ? What precisely is so surprising about this low entropy of the early universe ? Sure, that's a great question . You know, entropy is this idea we all have disorderly randomness, disorganization . It increases with time . It seems very natural . You're completely correct that if entropy has been increasing then it must have been lower in the past . The problem is we usually think about cosmology in terms of setting up initial conditions right you know you know there was it's all very vague a little bit illdefined but there's this feeling from our everyday experience that the way we think about physics is we set something up in a certain state everything you're used to except for time. Time is fundamental in this picture