On Mon, May 29, 2017 at 3:06 PM, Bruce Kellett <bhkell...@optusnet.com.au> wrote: > On 29/05/2017 10:42 pm, Telmo Menezes wrote: >> >> On Mon, May 29, 2017 at 2:26 PM, Bruce Kellett >> <bhkell...@optusnet.com.au> wrote: >>> >>> On 29/05/2017 6:26 pm, Telmo Menezes wrote: >>>> >>>> On Mon, May 29, 2017 at 3:26 AM, Bruce Kellett >>>> <bhkell...@optusnet.com.au> wrote: >>>>> >>>>> I would say that there is only one history leading to our present >>>>> state. >>>>> Whether you take an MWI view or a collapse view, the wave function >>>>> branches >>>>> deterministically at every point, so if you follow your current twig >>>>> back >>>>> down to the main trunk etc, there will be a unique path. >>>> >>>> I don't think we can say we are in a specific twig. Many things about >>>> out present state are unknown/undefined. I can imagine that there are >>>> many well-defined present states that are compatible with my current >>>> subjective state. >>> >>> >>> Sure, but we are talking about wave functions, not subjective states. >> >> Replace "subjective" with "incomplete knowledge". > > > Doesn't help. Of course our knowledge is incomplete, the wave function isn't > completely known either -- but the result of specific measurements are what > is at stake here, and they are known quantum states.
In my view, what's at stake here is the possibility of latent variables having some degree of freedom leading to the same macro states (provided that there is incomplete information about these macro states, as is the case for humans). >>>> In fact you can perform a quantum erasure experiment, and be sure that >>>> your current state goes through at least two different shortest paths >>>> to the root, and it becomes nonsensical to say that one is the >>>> "correct" one. I don't think anyone knows how far this can go into the >>>> macroscopic world, but I don't see any reason to believe that it >>>> doesn't. >>> >>> >>> I don't understand what you think you are getting in a quantum erasure >>> experiment. If the "which way" information that was gathered is erased, >>> normal interference patterns are seen in the double slit situation. The >>> two >>> paths (through the separate slits) are in unresolved superposition until >>> they hit the detector, when decoherence takes over. There are not two >>> separate worlds, and your state is the result of the superposed paths, >>> not >>> of either path separately. There is no ambiguity about which the the >>> "correct" path -- neither is, both contribute equally. >> >> I would say that the delayed choice version of the experiment makes it >> clear that there are two possible pasts that lead to the same present >> state -- they differ by one bit of information. > > > That is not what is implied by delayed choice quantum erasure. Whether an > interference pattern is seen or not is determined by whether the "which way" > information is erased or not. But whether it is or not, the interference is > only seen when coincidence measurements tell one which photons to count. And > the timing information necessary for coincidence determination is available > only *after* all decisions about erasure or not have been made, whether that > decision is made before or after the other photon of the entangled pair has > reached its detector. > > "Delayed choice" is perhaps a misleading phrase in this context, and it does > not lead to an ambiguity of path -- it merely tells whether there was an > intact superposition or not. I know, this is not what I am trying to say. I'll choose something much simpler: Suppose there is a computer running in an empty room. This computer is connected to a random number generator. At some point it uses the random value to decide if it's going to show a screen that is all green or all red. Nobody witnesses it. > > 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 everything-list+unsubscr...@googlegroups.com. > To post to this group, send email to everything-list@googlegroups.com. > 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 everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
