Thanks. I couldn't find the exact references. Is this the popular one? http://arxiv.org/abs/1205.2675
On 19 March 2014 13:57, meekerdb <[email protected]> wrote: > On 3/18/2014 5:07 PM, LizR wrote: > > On 19 March 2014 12:47, meekerdb <[email protected]> wrote: > >> But in general that would mean knowing the state of everything the >> system had interacted with in the past, since it is now entangled with >> them. So even if you suppose there is no collapse of the wavefunction, >> decoherence has the same effect. >> > > I was only asking about the theoretical possibility, given > unrealistically perfect information about the state of the system. > > > The universe (assuming unitary QM) is reversible. In fact from the > standpoint of QM there is no arrow of time - it's deterministic, just like > Laplace's universe. So, as always, when the word "possibility" is used > there has to be some context. To *calculate* a history of the universe > from it's present state would require knowing its *complete* present state, > including your mental state. Is that "theoretically possible"? I think it > involves a paradox of self-reference. > > > To put it another way, in the Game of Life, even with perfect > information, you can't trace the state of the system backwards because it > loses information. So even the laws of physics couldn't work backwards in a > universe based on the GOL. QM, I'm informed, doesn't lose information, so > (very much in theory) you could work backwards - or (less in theory) the > laws of physics could. > > > Yes the universe doesn't lose information like the GoL. But relative to > any point it loses information across spacetime horizons. So there's no > way to gather that information up into a calculation unless you have some > God's eye view from outside the universe, in which case you could see the > past anyway. > > There's a couple of nice papers about this by Yasunori Nomura: > arXiv:1205.267v2 is a popular exposition and arXiv:1205.5550v2 is a more > technical paper. > > Brent > > > I wasn't asking whether I could build a chronoscope and watch the past > happening on TV. > > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/d/optout. > > > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
