On 10/18/2018 12:16 PM, [email protected] wrote:
On Monday, October 15, 2018 at 11:17:56 AM UTC, Bruce wrote:
From: <[email protected] <javascript:>>
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.
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
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