On Friday, May 4, 2018 at 4:07:26 AM UTC, [email protected] wrote: > > > > On Thursday, May 3, 2018 at 11:52:00 PM UTC, Bruce wrote: > > From: *Brent Meeker* <[email protected]> > > > On 5/3/2018 4:03 PM, Bruce Kellett wrote: > > The problem, of course, is that this unitary operator is formed in the > multiverse, so to form its inverse we have to have access to the other > worlds of the multiverse. And this is impossible because of the linearity > of the SE. So although the mathematics of unitary transformations is > perfectly reversible, measurements are not reversible in principle in the > one world we find ourselves to inhabit. > > > I think we need a more precise term than "in principle" which could > confuesed with "mathematically". You really mean reversal is > *nomologically* impossible even though it's *mathematically* reversible. > It's more impossible that *FAPP* or *statistically* but not *logically* > impossible. :-) > > > Not doable "in principle" just means that there is no conceivable way in > which it could be done. It is not just a matter of difficulty, or that it > would take longer than the lifetime of the universe. It is actually > impossible. Quantum mechanics does not imply that all things that are > logically possible are nomologically possible, or could be achieved in > practice. That is why Saibal's claim that there exists a unitary operator > that does what he wants is rather empty -- there are an infinite number of > unitary operators that are not realizable in practice. And this limitation > is a limitation "in principle". > > Bruce > > > *If you take the view that quantum reality is irreducibly random, it MEANS > that there is no process in nature that can explain how a random event > could occur, for if such a process existed, it would contradict > "irreducibly random". Bruce seems to take the view that all measurements > are irreversible in principle. That might not be true. For example, suppose > the temperature of a system decreases. Isn't it hypothetically possible to > imagine a time reversal of all the IR photons which caused the cooling, to > reunite with the original system and restore the previous higher > temperature? If so, the cooling process in this example is reversible > albeit hugely improbable -- which I refer to as statistically reversible, > or irreversible FAPP. I think Bruce can give an example of a measurement > which is time irreversible in principle, that is, impossible to time > reverse. AG* >
*CORRECTION:Since Maxwell's equations are Lorentz invariant, I don't think Einstein had to modify them. The situation with mechanics was different; those laws were NOT Lorentz invariant and Einstein did in fact modify them. E&M allows for action at a distance, as does GR, at the SoL I don't think the issue is relevant to mechanics where all actions occur at points of contact. 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]. 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.
