On Thursday, October 18, 2018 at 8:33:10 PM UTC, Brent wrote: > > > > On 10/18/2018 12:16 PM, [email protected] <javascript:> wrote: > > > > On Monday, October 15, 2018 at 11:17:56 AM UTC, Bruce wrote: >> >> From: <[email protected]> >> >> >> On Sunday, October 14, 2018 at 5:08:42 PM UTC, smitra wrote: >>> >>> On 14-10-2018 15:24, [email protected] wrote: >>> > In a two state system, such as a qubit, what forces the interpretation >>> > that the system is in both states simultaneously before measurement, >>> > versus the interpretation that we just don't what state it's in before >>> > measurement? Is the latter interpretation equivalent to Einstein >>> > Realism? And if so, is this the interpretation allegedly falsified by >>> > Bell experiments? AG >>> >>> It is indeed inconsistent with QM itself as Bell has shown. Experiments >>> have later demonstrated that the Bell inequalities are violated in >>> precisely the way predicted by QM. This then rules out local hidden >>> variables, therefore the information about the outcome of a measurement >>> is not already present locally in the environment. >>> >>> Saibal >>> >> >> What puzzles me is this; why would the Founders assume that a system in a >> superposition is in all component states simultaneously -- contradicting >> the intuitive appeal of Einstein realism -- when that assumption is not >> used in calculating probabilities (since the component states are >> orthogonal)? AG >> >> >> I think the problem arises with thinking of a superposition as an >> expression of a fact of the system being in all components of the >> superposition simultaneously. This mistaken interpretation leads to the >> Schrödinger cat paradox, which you have worried about for a while. >> >> But this is a mistake. A superposition is just an expansion of a wave >> function in some basis or the other -- the choice of basis is arbitrary, so >> it makes no sense to think of this expansion as representing anything that >> happens in "reality" (in Einstein's sense of "reality"). The state is still >> the original state until decoherence kicks in >> > > > *Here's where I think you're mistaken. When the box is closed in the Cat > experiment, time continues to increase, so the wf evolves independent of > decoherence; before it sets in; before it takes effect, however short that > duration might be. But since the expansion of the superposition is > arbitrary wrt the basis used in the expansion, it still makes no sense to > attribute any physical reality to it, much less a simultaneous state of all > components. Do agree with this? TIA, AG * > > > This example gets confused. Schroedinger intended it to be absurd and it > was absurd not only because the cat was both alive and dead at the same > time but also because it suddenly changed to one or the other when he > looked in. In fact there can be non "wf evolves independent of coherence" > when the box is closed. The cat, the box, the very spacetime field of the > radioactive decay products are enough for decoherence to have occurred. > The over idealization makes it hard to discuss these because all talk of > the cat in a superposition is metaphorical. It would be much clearer if > you just discussed a single radioactive atom, say a beta emitter, in a > "box" that is just a location you can inspect in the vacuum. Until you > test it the atom is in a superposition of decayed and not-decayed. > Whenever it decays, that is a definite event; the state of the atom > decoheres into mixture of decayed or not-decayed because of interaction > with the degrees of freedom of the electron and anti-neutrino fields. So > the superposition is best thought of as your mathematical representation of > the atom, which changes when you test it. > > I've assumed that your test is just for decayed vs not-decayed. But you > could also consider the direction of emission by looking at the recoil of > the atom. In that case your not-decayed state is a superposition of all > possible recoil directions you can measure and the decayed state > corresponds with just one of those directions. > > > >> and then, because of einselection of a preferred basis, we can say that >> the separate states are "real" -- namely orthogonal, so that one other >> other is chosen. Until that time, the only state around is the original >> state, as can be demonstrated by the possibility of recoherence, in which >> case you recover just the initial state and nothing else. >> > > *I can see how recoherence is impossible FAPP, but after some time elapses > the state of the cat could Dead or Alive; not necessarily the original > state, Alive. A*G > > > When recoherence is no longer possible that's a real physical change. The > system has evolved. >
*Since decoherence is a unitary process, isn't recoherence is always possible, even if not FAPP? AG* > > Brent > > >> So for Schrödinger's cat, for example, if you could recohere the system >> after one hour, say, you would find the cat alive in the box and the vial >> of cyanide unbroken with the radioactive atom undecayed -- exactly as you >> set the system up. It is only because the cat and apparatus are large warm >> classical objects that this recoherence is not possible FAPP. To think of >> the cat at some intermediate time as being both dead and alive is just a >> confusion -- it is at all times either one or the other. >> > > *The Cat does have an intermediate state since time is evolving causing > the wf to evolve, but as I argue above, it's not in both states of the > superposition because the choice of basis is arbitrary, and by extension, > certainly not in both states simultaneously. I generally agree with your > arguments, which I articulated half-a-dozen times or more last summer, but > no one here seemed to understand or agree. When you remind us that the > choice of basis is arbitrary, this is KEY, and all one has to do is apply > what's anathema to see the seminal error; common sense applied to the fact > that the basis used in the superposition is arbitrary! It seems there > remains an undeserved impulse, a cottage industry as it were, to claim some > mysteries in QM that don't exist. AG * > >> >> Bruce >> > -- > 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.
