On Tuesday, July 31, 2018 at 7:14:53 PM UTC, Brent wrote:
On 7/31/2018 6:43 AM, agrays...@gmail.com <javascript:> wrote:
On Tuesday, July 31, 2018 at 6:11:18 AM UTC, Brent wrote:
On 7/30/2018 9:21 PM, agrays...@gmail.com 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 *
That it is impossible to isolate the cat is the source of the
absurdity...not that it exists in a superposition later.
*But if you claim the cat decoheres in some exceedingly short time
based on decoherence theory and the wf you write, taking into
account the apparatus, observer, and remaining environment, mustn't
the cat be initially isolated for this to make sense? AG*
