On Mon, May 29, 2017 at 2:26 PM, Bruce Kellett <[email protected]> wrote: > On 29/05/2017 6:26 pm, Telmo Menezes wrote: >> >> On Mon, May 29, 2017 at 3:26 AM, Bruce Kellett >> <[email protected]> wrote: >>> >>> On 29/05/2017 9:45 am, Pierz wrote: >>> >>> WRT to this whole multi-coloured T-Rex business, there is a simpler point >>> to >>> be made. My original argument was in favour of MWI. Now whether, in MWI, >>> macroscopic histories can merge is surely an interesting puzzle. But >>> without >>> MWI, there cannot be any ambiguity about the colour of T-Rexes. In a >>> single >>> universe interpretation of QM, T-Rexes were blue or they were red and >>> they >>> can't exist in a superposition of both. The past can't turn back into a >>> mush >>> of probabilities, because that would imply either that there is some "3p" >>> significance to the concept of "now", or that the past consists of many >>> worlds. In other words I am asserting that, sans MWI, any ambiguity about >>> the past is a matter of ignorance, not of quantum uncertainty. Otherwise >>> you >>> are saying that past moments which once were well defined are somehow >>> dissolved back into ambiguity by the passage of time. But that would be >>> privileging the now with some kind of absolute significance, which is >>> untenable. All nows are equal. >>> >>> Another way of stating my argument is that the following three >>> propositions >>> are mutually incompatible: >>> >>> There is a single history >>> There is no objective significance to the concept of the current moment >>> ("now") >>> The future is objectively uncertain >>> >>> You can take your pick which of those propositions you reject, but it's >>> logically impossible to support all three. >>> >>> >>> 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". >> 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. > 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. -- 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.
