On Tuesday, July 31, 2018 at 6:11:18 AM UTC, Brent wrote: > > > > On 7/30/2018 9:21 PM, agrays...@gmail.com <javascript:> 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. >
*When you start your analysis /experiment using decoherence theory, don't you assume the cat is isolated from the environment? It must be if you say it later decoheres (even if later is only a nano second). Why is this not a problem if, as you say, it is impossible to isolate the cat? AG * > > *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. > > > *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 * > > > It's not a fallacy. It just doesn't apply to the cat or other macroscopic > objects, with rare laboratory exceptions. > *Other than slit experiments where superposition can be interpreted as the system being in both component states simultaneously, why is this interpretation extendable to all isolated quantum systems? AG * > Any old plane polarized photon can be represented as being in a > superposition of left and right circular polarization. It is *not* the > case that a system is in all basis states at once unless you count being in > state *|x>* with zero amplitude as being in *x*. > > Brent > > > >> 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 everything-li...@googlegroups.com. >> To post to this group, send email to everyth...@googlegroups.com. >> 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 everything-li...@googlegroups.com <javascript:>. > To post to this group, send email to everyth...@googlegroups.com > <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 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.
