# Unitarity and quantum cosmology

+ 1 like - 0 dislike
21 views

By studying quantum cosmology I was asking myself if the fact that the universe is expanding, so space is expanding and with it I would say that phase space is also expanding, so it's a non-unitary evolution, am I right? If yes, can unitarity be restored in a multiverse picture? Because I am always troubled when I hear that as we have experimentally verified the unitarity of low energy QM, by pushing further we arrive at the concluse that the multiverse can be extended from $t= - \infty$ to $t= + \infty$, sounds a bit dogmatic to me.

This post imported from StackExchange Physics at 2014-05-01 12:19 (UCT), posted by SE-user toot
asked Jun 11, 2012
See physics.stackexchange.com/questions/15571/… and physics.stackexchange.com/questions/26883/…

This post imported from StackExchange Physics at 2014-05-01 12:19 (UCT), posted by SE-user genneth
Short answer: no. More complicatedly, it's hard to define what time evolution is cosmologically. For observable consequences, usually "cosmological" really means "only the largest scale degrees of freedom", which is not special as a quantum system, and as long as one has a clock somehow (which need not be tied to this very coarse spacetime structure), evolution will be unitary. Once you include everything, however, the issue of "what's a clock" rears its ugly head.

This post imported from StackExchange Physics at 2014-05-01 12:19 (UCT), posted by SE-user genneth

 Please use answers only to (at least partly) answer questions. To comment, discuss, or ask for clarification, leave a comment instead. To mask links under text, please type your text, highlight it, and click the "link" button. You can then enter your link URL. Please consult the FAQ for as to how to format your post. This is the answer box; if you want to write a comment instead, please use the 'add comment' button. Live preview (may slow down editor)   Preview Your name to display (optional): Email me at this address if my answer is selected or commented on: Privacy: Your email address will only be used for sending these notifications. Anti-spam verification: If you are a human please identify the position of the character covered by the symbol $\varnothing$ in the following word:p$\hbar$ysicsOver$\varnothing$lowThen drag the red bullet below over the corresponding character of our banner. When you drop it there, the bullet changes to green (on slow internet connections after a few seconds). To avoid this verification in future, please log in or register.