On Tue, Jul 31, 2018 at 4:52 PM Brent Meeker <meeke...@verizon.net> wrote:
> > > On 7/31/2018 2:38 PM, Jason Resch wrote: > > > > On Tuesday, July 31, 2018, Brent Meeker <meeke...@verizon.net> wrote: > >> >> >> On 7/31/2018 9:46 AM, Jason Resch wrote: >> >> >> >> On Tue, Jul 31, 2018 at 1:11 AM Brent Meeker <meeke...@verizon.net> >> wrote: >> >>> >>> >>> On 7/30/2018 9:21 PM, agrayson2...@gmail.com wrote: >>> >>> >>> >>> On Tuesday, July 31, 2018 at 1:34:58 AM UTC, Brent wrote: >>>> >>>> >>>> >>>> On 7/30/2018 4:40 PM, agrays...@gmail.com wrote: >>>> >>>> >>>> >>>> On Monday, July 30, 2018 at 7:50:47 PM UTC, Brent wrote: >>>>> >>>>> >>>>> >>>>> On 7/30/2018 8:02 AM, Bruno Marchal wrote: >>>>> >>>>> *and claims the system being measured is physically in all eigenstates >>>>> simultaneously before measurement.* >>>>> >>>>> >>>>> >>>>> Nobody claims that this is true. But most of us would I think agree >>>>> that this is what happens if you describe the couple “observer particle” >>>>> by >>>>> QM, i.e by the quantum wave. It is a consequence of elementary quantum >>>>> mechanics (unless of course you add the unintelligible collapse of the >>>>> wave, which for me just means that QM is false). >>>>> >>>>> >>>>> This talk of "being in eigenstates" is confused. An eigenstate is >>>>> relative to some operator. The system can be in an eigenstate of an >>>>> operator. Ideal measurements are projection operators that leave the >>>>> system in an eigenstate of that operator. But ideal measurements are rare >>>>> in QM. All the measurements you're discussing in Young's slit examples >>>>> are >>>>> destructive measurements. You can consider, as a mathematical >>>>> convenience, >>>>> using a complete set of commuting operators to define a set of eigenstates >>>>> that will provide a basis...but remember that it's just mathematics, a >>>>> certain choice of basis. The system is always in just one state and the >>>>> mathematics says there is some operator for which that is the eigenstate. >>>>> But in general we don't know what that operator is and we have no way of >>>>> physically implementing it. >>>>> >>>>> Brent >>>>> >>>> >>>> *I can only speak for myself, but when I write that a system in a >>>> superposition of states is in all component states simultaneously, I am >>>> assuming the existence of an operator with eigenstates that form a complete >>>> set and basis, that the wf is written as a sum using this basis, and that >>>> this representation corresponds to the state of the system before >>>> measurement. * >>>> >>>> >>>> In general you need a set of operators to have the eigenstates form a >>>> complete basis...but OK. >>>> >>>> *I am also assuming that the interpretation of a quantum superposition >>>> is that before measurement, the system is in all eigenstates >>>> simultaneously, one of which represents the system after measurement. I do >>>> allow for situations where we write a superposition as a sum of eigenstates >>>> even if we don't know what the operator is, such as the Up + Dn state of a >>>> spin particle. In the case of the cat, using the hypothesis of >>>> superposition I argue against, we have two eigenstates, which if "occupied" >>>> by the system simultaneously, implies the cat is alive and dead >>>> simultaneously. AG * >>>> >>>> >>>> Yes, you can write down the math for that. But to realize that >>>> physically would require that the cat be perfectly isolated and not even >>>> radiate IR photons (c.f. C60 Bucky ball experiment). So it is in fact >>>> impossible to realize (which is why Schroedinger considered if absurd). >>>> >>> >>> * CMIIAW, but as I have argued, in decoherence theory it is assumed the >>> cat is initially isolated and decoheres in a fraction of a nano second. So, >>> IMO, the problem with the interpretation of superposition remains. * >>> >>> >>> Why is that problematic? You must realize that the cat dying takes at >>> least several seconds, very long compared to decoherence times. So the cat >>> is always in a *classical* state between |alive> and |dead>. These are >>> never in superposition. >>> >>> *It doesn't go away because the decoherence time is exceedingly short. * >>> >>> >>> Yes is does go away. Even light can't travel the length of a cat in a >>> nano-second. >>> >>> >> >> What if the cat is on Pluto for this one hour? Would it not be perfectly >> isolated from us on Earth, and thus remain in a superposition until the the >> several hours it takes for light to get to Earth from Pluto reaches us? >> >> >> ?? Are you assuming that decoherence only occurs when humans (or >> Earthlings) observe the event? >> >> >> Brent >> > > > No, just that superposition is a relative, rather than objective notion. > > > OK. Welcome to QBism. > After reading the wiki article on QBism I still can't say I understand what it is about, as it doesn't seem to offer any core positions. I am an adherent of bayesianism, and believe it applies generally in all domains (being an agent having to make decisions/bets), so what does QBism add if one already accepts a general reliance on Bayes theorem? It doesn't seem like QBism takes any strong position on any of the quantum paradoxes, nor offer any insights to addressing or explaining them. In this it seems like a pretty empty theory, with hints towards the "instrumentalist" and "shut up and calculate" mindsets--that only the probability matters. To the extent that is true, I reject QBism. While QBism might not put forward anything that is false, the attitude it conveys seems like it would stymie progress towards advancing our understanding of reality. That superposition is relative does not require observers or knowledge, it is a consequence of the postulates of QM. Either system A has interacted with system B and they are both part of the superposition together, or they have not interacted yet and system A will be in a superposition of various possible states to system B, and system B will be in a super position of various states to system A. Jason -- 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.
