On Tue, Jul 31, 2018 at 1:11 AM Brent Meeker <[email protected]> wrote:
> > > On 7/30/2018 9:21 PM, [email protected] wrote: > > > > On Tuesday, July 31, 2018 at 1:34:58 AM UTC, Brent wrote: >> >> >> >> On 7/30/2018 4:40 PM, [email protected] 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? 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 [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.
