On Wednesday, May 23, 2018 at 5:54:29 PM UTC, Brent wrote: > > > > On 5/22/2018 11:53 PM, [email protected] <javascript:> wrote: > > > > 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. Why would information be lost to > some other world simply because one value of the pair of probabilities > equals 0? > > > It wouldn't if the SE caused it to evolve to 0. But in the cases of > interest the SE causes the reduced density matrix to evolve to non-zero > diagonal elements and the cross terms to be zero FAPP (but not exactly) so > that it approximates a mixed state density matrix. Then we say each > diagonal element is the probability amplitude of a "world" as if the off > diagonal terms were exactly zero. >
Do you have some good links which explains this? Also, I think these other "worlds" are just inaccessible, disjointed subspaces corresponding to the values which are NOT measured in this world, and this concept has been distorted for (and by) the hoi polloi to mean actual, full blown, copies of this world, including copies of the original observer, his/her memories, and so forth. Is this your understanding as well; that these full blown copies of this world and its observer do NOT exist? Furthermore, I find the disjointedness of these subspaces hard to grasp intuitively, since they all originated with decoherence using this world's environment. 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? > > > No. The information that is in the environment due to decoherence is > different for different measurement results (i.e. "worlds"). According to > Zurek this is what makes "worlds" classical, i.e. within one "world" the > result of a quantum measurement is copied in many places in the environment > so that all different observers (in that "world") agree on the result. > > Isn't decoherence therefore in conflict with the MWI? AG > > > No. Decoherence is a partial explanation for how the different "worlds" > branch off. > > Brent > > >> Brent >> > -- > 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] <javascript:>. > To post to this group, send email to [email protected] > <javascript:>. > Visit this group at https://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/d/optout. > > > -- 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.
