On Wednesday, February 12, 2020 at 3:49:53 AM UTC-7, Bruce wrote: > > On Wed, Feb 12, 2020 at 9:32 PM Alan Grayson <[email protected] > <javascript:>> wrote: > >> On Tuesday, February 11, 2020 at 12:44:38 PM UTC-7, Brent wrote: >>> >>> >>> >>> I think decoherence theory is a big step forward in describing the >>> quantum->classical emergence. It was also a step forward in solving the >>> measurment problem. But it has still left gaps. It shows how the density >>> matrix becomes diagonalized in a measurement process. BUT only FAPP. And >>> it doesn't explain why only one diagonal value is realized (MWI wants to >>> keep them all) or the Born rule. I'm presently reading Ruth Kastner's book >>> on the "Possibilist Transactional Interpretation" which is her version of >>> Cramer's TI. Her basic idea, which could be applied to MW as well as TI, >>> is that all the mathematical evolution takes place in possibility space, >>> which is just as real as Hilbert space or wave-functions...but not as real >>> as spacetime, and then one result, at random (and she justifies the Born >>> rule) is actualized (which is a step better than realized). Metaphysically >>> it is like MWI in practice, you calculate what happens in the many worlds >>> and then you throw all but one away. The main difference is PTI depends on >>> the idea of absorbers to define when a measurement is completed. The >>> absorbers in a measurement are like the environment in decoherence, but >>> there are also particle level absorbers...which I haven't finished reading >>> about yet. >>> >>> Brent >>> >> >> You (and Bruce) are on the same page wrt unitary time evolution for the >> measurement process; namely, that it's violated. OTOH, you (and Bruce) like >> decoherence theory. According to Wiki, when the environment is included in >> the measurement process, the total process satisfies unitary time >> evolution, whereas the total process excluding the environment creates just >> the appearance of violating unitary time evolution. Is this your >> assessment; that unitary time evolution in the measurement process is >> satisfied when the environment is taken into account? TIA, AG >> > > Decoherence is unitary interaction with the environment. That is not the > problem. The thing is that that isn't a complete solution of the > measurement problem. >
Right. Decoherence theory doesn't tell us what will be measured, which I assume is the complete solution of the measurement problem. AG > > The difficulty I am pointing to is somewhat different. It is clear that > unitary evolution based on the Schrodinger equation cannot account for > scientific observations. Unitarity is not really the problem. The problem > is that unitary evolution can give only one brach or world for each basis > state in the superposition. This rules out any application of the Born rule. > ISTM, that the only way we know that Born's rule is valid, is to take an ensemble of outcomes and compare them with the predictions of the rule. Why can't we do this in the context of many branches; just create an ensemble of measurements in this world, and see that the result is what Born's rule predicts? I mean just ignore the hypothetical measurements in the other branches, which we cannot in principle observe anyway. AG > > Bruce > -- 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 view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/365dac8b-23cd-4971-bd6d-bf7782585694%40googlegroups.com.
