On Wednesday, May 2, 2018 at 10:01:38 PM UTC, Brent wrote: > > > > On 5/2/2018 2:44 PM, [email protected] <javascript:> wrote: > > > > On Wednesday, May 2, 2018 at 6:01:28 PM UTC, Brent wrote: >> >> >> >> On 5/2/2018 4:48 AM, [email protected] wrote: >> >> >> >> On Monday, April 30, 2018 at 3:33:23 AM UTC, [email protected] wrote: >>> >>> Implied by standard QM insofar as the theory is inherently irreversible, >>> that is, irreversible in principle at the quantum level since the wf cannot >>> be recovered by time reversal. AG >>> >> >> I argued this conclusion on the Entanglement thread. Here I will add some >> additional considerations. When you think of time reversibility, say for an >> electron being measured by SG device, you naturally think of passing the >> measured electron backward along the same path, trying to recover the >> original wf by running time backward. Of course you can't run time backward >> during or even after a measurement because QM doesn't provide any time >> dependent equations for the measurement process. But even if you could do >> the thought experiment, according to QM, if the measurement was, say, spin >> UP, it remains spin UP by virtue of the measurement postulates of QM. >> Further, This MUST be the backward in time measurement result if you simply >> accept time symmetry, and not appeal to the measurement postulates of QM. >> Thus, it seems highly plausible that the original wf, a superposition, >> cannot be recovered after the measurement, and that QM is a time >> IRREVERSIBLE theory. AG >> >> >> In MWI the is both a spin UP and a spin DOWN, as projections on >> orthogonal subspaces. The theory is mathematically reversible in the sense >> that if you reversed the evolution of the state vector it would reverse the >> projection in both subspaces. >> > >> Brent >> > > In MWI and CI we have projection operators, aka in CI as collapse. Aren't > they all non unitary regardless of the interpretation, implying IIUC, that > they can't be time-reversed. AG > > > Yes, a projection operator is non-unitary. Maybe I didn't phrase it well, > but that's why I avoided invoking projection operators. The subspaces > become orthogonal in the approximation that we can average out the cross > terms, but that approximation is only a good one when decoherence has taken > place. > > Brent >
To avoid confusion, please distinguish between the MWI and CI when making claims. I have been limiting my remarks to CI. Does decoherence occur in both interpretations? I see decoherence as a unitary process. Is this correct? I don't understand your comments about averaging out the cross terms. AG > > > -- > 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] <javascript:>. > To post to this group, send email to [email protected] > <javascript:>. > Visit this group at https://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 https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
