On 4/28/2018 4:06 PM, [email protected] wrote:
On Saturday, April 28, 2018 at 10:55:13 PM UTC, [email protected] wrote:On Saturday, April 28, 2018 at 9:33:58 PM UTC, Brent wrote: On 4/28/2018 9:39 AM, [email protected] wrote: > Is it a settled issue whether measurements in QM are strictly > irreversible, There are interactions that, if you did not arrange that they be erased, would constitute measurements. Whether you say they were measurements and then got erased or they are not measurments because they didn't produce an irreversible record is a phlosophical or semantic question. > that is irreversible in principle, or just statistically irreversible, > that is, reversible but with infinitesimal probability? TIA, The equations are all reversible so you might say they are reversible with infinitesimal probability...but in most cases that reversal would mean catching and reversing photons that are already on their way outbound beyond the orbit of the Moon. Brent Are there any measurements that can't be reversed regardless of the fact that the equations of physics are time reversible? I could swear, and I DO, that Bruce demonstrated such a case for spin 1/2 particles measured by SG device. AG You can always take a movie of the measurement and play it backward. Does this say anything about reversal in principle; that every measurement is in principle reversible? AG
If you can look at the movie played in reverse and recognize that what it depicts is nomologically impossible, that means things aren't reversible. If it looks nomologically possible, then that means it's approximately reversible and that you're probably missing stuff that can't be seen (e.g. IR photons).
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