On Wednesday, May 23, 2018 at 9:15:47 AM UTC, [email protected] wrote: > > > > On Wednesday, May 23, 2018 at 8:53:07 AM UTC, [email protected] wrote: >> >> >> >> On Wednesday, May 23, 2018 at 8:16:07 AM UTC, Bruce wrote: >>> >>> From: <[email protected] >>> >>> On Wednesday, May 23, 2018 at 7:09:31 AM UTC, Bruce wrote: >>>> >>>> From: <[email protected]> >>>> >>>> >>>> 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 >>> >>> >>> You describe the evolution of a quantum state to a different state -- >>> you are not describing a measurement operation. If you measure a different >>> state, you can expect different results. >>> >> >> Doesn't the SWE evolve an initial quantum state into another, and >> another, and so on, and the probability amplitude of each state in the >> original superposition changes? If so, I was just describing how the >> probabilities of each eigenstate changes, keeping the sum of probabilities >> equal to unity. So far, no measurement, and all information in this world. >> When a measurement occurs, the probability density of all eigenstates >> (except for the eigenstate of the measured value) goes to zero, and all >> probability is concentrated around the measurement value, with the result >> being a delta function in probability density. Throughout, all information >> remains in this world. How information associated with the other branches >> becomes inaccessible under decoherence I don't understand. I'll read up on >> this issue. AG >> > > Let's assume that the other branches are inaccessible, meaning, IIUC, that > their entanglements are inaccessible and therefore that the measurement in > this world can't be reversed in principle. How do you go from this > conclusion, to the conclusion that all these inaccessible subspaces have > MEASURED values corresponding to each of the eigenstates corresponding to > each branch? AG >
This must be the answer; the inaccessible entanglements in each branch ARE the respective measurements; a somewhat elegant result. No copies of observers or entire worlds. I think I like it. 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 > > > That is a measurement on a different state, where one would expect > different results. > > 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 > > > Initially yes. But decoherence diagonalizes the density matrix FAPP, so > the other branches become unreachable. That is what one means by separate > worlds. > > 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.
