tag:blogger.com,1999:blog-5880610.post4182605604062881580..comments2020-06-16T02:04:06.312-04:00Comments on Information Processing: Instability of Quantum de Sitter SpacetimeSteve Hsuhttp://www.blogger.com/profile/02428333897272913660noreply@blogger.comBlogger3125tag:blogger.com,1999:blog-5880610.post-32907058334470131722015-01-06T20:47:58.210-05:002015-01-06T20:47:58.210-05:00In semiclassical QFT, the energy-momentum tensor i...In semiclassical QFT, the energy-momentum tensor is dS invariant, full stop. But the real world is certainly tricky, because gravitational backreaction is the whole point, so semiclassical QFT isn't necessarily up to the task. You would have to convince me that quantum gravity somehow breaks dS invariance -- which is always possible, I suppose, though I don't see why it would happen. Sean Carrollnoreply@blogger.comtag:blogger.com,1999:blog-5880610.post-25295620860571229482015-01-06T20:31:43.704-05:002015-01-06T20:31:43.704-05:00Looks like we are in for a long conversation :-) ...Looks like we are in for a long conversation :-) I think I know where we disagree, but it will take some time to write it up in comprehensible form -- I'll send you an email. I don't think you need "out of equilibrium detectors" for the system to evolve away from the stationary state you consider. The state of the universe we describe (QFT modes thermalized; gravitational back steve hsuhttp://plus.google.com/u/0/+StephenHsu/aboutnoreply@blogger.comtag:blogger.com,1999:blog-5880610.post-41789229491946145422015-01-06T17:33:29.136-05:002015-01-06T17:33:29.136-05:00Sorry Steve, I don't buy it. :) It's true ...Sorry Steve, I don't buy it. :) It's true that particle detectors in dS detect a thermal bath of particles. But such particle detectors are, by construction, out-of-equilibrium systems. In the actual dS vacuum, there are no such detectors hanging around, and correspondingly there is no thermal bath violating the symmetries of dS. There is just the vacuum state itself, whose Sean Carrollnoreply@blogger.com