On 2/6/2017 9:12 AM, Stathis Papaioannou wrote:
On Mon., 6 Feb. 2017 at 11:06 pm, Ronald Held <ronaldh...@gmail.com <mailto:ronaldh...@gmail.com>> wrote:Why Boltzmann Brains Are Bad Authors: Sean M. Carroll Comments: 27 pages. Invited submission to a volume on Current Controversies in Philosophy of Science, eds. Shamik Dasgupta and Brad Weslake Subjects: High Energy Physics - Theory (hep-th); Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); History and Philosophy of Physics (physics.hist-ph) Some modern cosmological models predict the appearance of Boltzmann Brains: observers who randomly fluctuate out of a thermal bath rather than naturally evolving from a low-entropy Big Bang. A theory in which most observers are of the Boltzmann Brain type is generally thought to be unacceptable, although opinions differ. I argue that such theories are indeed unacceptable: the real problem is with fluctuations into observers who are locally identical to ordinary observers, and their existence cannot be swept under the rug by a choice of probability distributions over observers. The issue is not that the existence of such observers is ruled out by data, but that the theories that predict them are cognitively unstable: they cannot simultaneously be true and justifiably believed. -- Here is the link: https://arxiv.org/pdf/1702.00850.pdfEverything I've ever seen written about Boltzmann Brains takes the position that they are obviously absurd. But here's another view: Boltzmann Brains would give rise to every possible thought - every possible observer moment. This is equivalent to the situation whereby every possible observer moment exists necessarily as a Platonic entity, without the need for a separate physical universe. The appearance of a stable physical universe then emerges from the ensemble of these observer moments.
Which means that appearance of a stable physical universe cannot be taken as evidence for anything at all - including our thoughts about Boltzmann brains.
Carroll argues that there are no fluctuations of the vacuum and hence no Boltzmann brain problem:
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