On Tuesday, July 31, 2018 at 1:34:58 AM UTC, Brent wrote: > > > > On 7/30/2018 4:40 PM, [email protected] <javascript:> 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. It doesn't go away because the decoherence time is exceedingly short. And for this reason I still conclude that Schroedinger correctly pointed out the fallacy in the standard interpretation of superposition; namely, that the system represented by a superposition, is in all components states simultaneously. AG * > > Brent > > -- > 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] <javascript:>. > To post to this group, send email to [email protected] > <javascript:>. > 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.
