On Wednesday, May 23, 2018 at 7:09:31 AM UTC, Bruce wrote: > > From: <[email protected] <javascript:>> > > > On Wednesday, May 23, 2018 at 4:44:30 AM UTC, Brent wrote: >> >> >> On 5/22/2018 9:41 PM, [email protected] wrote: >> >> >> On Wednesday, May 23, 2018 at 4:05:58 AM UTC, Brent wrote: >>> >>> >>> >>> On 5/22/2018 8:29 PM, [email protected] wrote: >>> >>> >>> >>> On Wednesday, May 23, 2018 at 2:24:07 AM UTC, Bruce wrote: >>>> >>>> From: <[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 lost to >>>>> the environment is different depending on what the result is. So if by >>>>> some magic you could reverse your world after seeing the result 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. >>>> >>>> Bruce >>>> >>> >>> Consider this interpretation of the wf, which for simplicity I consider >>> as a superposition of two eigenfunctions, and based on the probability >>> amplitudes represents a 50% probability of each outcome at some point in >>> time. Since the measurement hasn't occurred, where does this information >>> reside? Presumably it all resides in THIS world. As time evolves the >>> probability distribution changes, say to 75-25, and later to 90-10, and so >>> on. All of this information resides in this world since without a >>> measurement occurring, there are no other worlds, and no collapse. Suppose >>> at some point in time, the values changed to 100-0, Isn't 100-0 as good as >>> other pair if they sum to zero? And why would anyone think another world >>> comes into existence because one of the values evolved to 0? I will now >>> define, in answer to one of Brent's questions, when the measurement occurs. >>> I assert it occurs when one of the pair of values equals 0, All throughout >>> all information was in this world. Why would another world come into >>> existence if one of the values happened to be 0? AG >>> >>> >>> First, in the cases of interest there is no mechanism for going from >>> 50/50 to 100/0 because it goes 0/100 as well, and it's random. You may >>> hypothesize there is such process, but that's equivalent to assuming a >>> hidden variable. And then Aspect's experiments show such a hidden variable >>> transmits influence faster than light...which then cascades into problems >>> with special and general relativity and quantum field theory and so on... >>> >>> Brent >>> >> >> I was assuming the wf evolves to different probabilities via the SWE. >> Nothing wrong with going to 0/100 because that just means the other >> eigenvalue became the final state. AG >> >> >> That's why I wrote "in cases of interest". If it evolves to 0/100 via >> the SWE no problem...no interest either. >> > > Why no interest? Haven't I described the case of a system evolving > according to the SWE, then a measurement occurring, and throughout all the > information is residing in THIS world. > > > Your thought experiment does not correspond to unitary quantum evolution. >
Why not? Would different intermediate values correspond to unitary quantum evolution? AG > > Why would information be lost to some other world simply because one value > of the pair of probabilities equals 0? > > > If one of the probabilities is zero, it means that the wave function has > no corresponding component. If the only other part of the wave function has > probability 100%, then the outcome is certain, and no information can > reside anywhere else. > I was trying to describe a situation where the wf collapses, in terms of probability, to a delta function, where a single outcome is achieved with 100% probability, and the other does not, so it has probability of 0. AG > > IOW, the example is meant to illustrate the fallacy of claiming some > information is lost when the measurement occurs, and now resides in some > inaccessible other world. In decoherence, isn't all the lost information > lost in THIS world, to the environment, like a heat bath? Isn't decoherence > therefore in conflict with the MWI? AG > > > No. Decoherence occurs independently for each branch of the wave function, > so information is disseminated into the environment in all branches of the > wave function independently. > OK, but how does one jump to the assumption of other worlds? Doesn't each "branch" exist in this world? 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 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.
