On Tuesday, July 31, 2018 at 4:47:13 PM UTC, Jason wrote: > > > > On Tue, Jul 31, 2018 at 1:11 AM Brent Meeker <[email protected] > <javascript:>> wrote: > >> >> >> On 7/30/2018 9:21 PM, [email protected] <javascript:> 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 >
*In principle, superposition represents a system prior to measurement. Nothing to do with when light reaches the Earth; depends on when the measurement occurs. AG* -- 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.
