From: <[email protected] <mailto:[email protected]>>
On Wednesday, May 23, 2018 at 1:45:39 AM UTC, Brent wrote: On 5/22/2018 5:59 PM, [email protected] wrote:On Wednesday, May 23, 2018 at 12:44:06 AM UTC, Brent wrote: On 5/22/2018 3:46 PM, [email protected] wrote:On Tuesday, May 22, 2018 at 10:41:11 PM UTC, [email protected] wrote: I did, but you're avoiding the key point; if the theory is on the right track, and I think it is, quantum measurements are irreversible FAPP. The superposition is converted into mixed states, no interference, and no need for the MWI.You're still not paying attention to the problem. First, the superposition is never converted into mixed states. It /approximates/, FAPP, a mixed state/in some pointer/ basis (and not in others). Second, even when you trace over the environmental terms to make the cross terms practically zero (a mathematical, not physical, process) you are left with different outcomes with different probabilities. CI then just says one of them happens. But when did it happen?...when you did the trace operation on the density matrix? I think the main takeaway from decoherence is that information isn't lost to other worlds, but to the environment in THIS world.But that ignores part of the story. The information that is lostto the environment is different depending on what the result is. So if by some magic you could reverse your world after seeing theresult you couldn't get back to the initial state because you could not also reverse the "other worlds".What "other worlds"? If they don't exist, why should I be concerned about them? AG
I think you are ignoring the facts of the mathematics of unitary evolution of the wave function. Under unitary evolution the wave function branches, one branch or each element of the superposition, which is, one branch for each possible experimental result. These branches are in the mathematics. Now you can take all branches as really existing every much as the observed result exists -- that is the MWI position. Or you can throw them away as not representing your experimental result -- which is the collapse position. But in both cases, the evolution of the wave function shows that there is information in each mathematical branch. If you discard the branches (collapse) you throw this information away: if you retain the branches as other worlds, the information becomes inaccessible by decoherence and partial tracing.
The situation is the same in either approach. Brent and I are not being inconsistent, devious, or otherwise tricky by referring to both MWI and CI approaches -- we are just recognizing the actual mathematics of quantum mechanics. The mathematics has to be interpreted, and different interpretations are available for the way in which the information in other branches is treated.
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