On 7/31/2018 2:38 PM, Jason Resch wrote:
On Tuesday, July 31, 2018, Brent Meeker <meeke...@verizon.net
<mailto:meeke...@verizon.net>> wrote:
On 7/31/2018 9:46 AM, Jason Resch wrote:
On Tue, Jul 31, 2018 at 1:11 AM Brent Meeker
<meeke...@verizon.net <mailto:meeke...@verizon.net>> wrote:
On 7/30/2018 9:21 PM, agrayson2...@gmail.com
<mailto:agrayson2...@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.
*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.
What if the cat is on Pluto for this one hour? Would it not be
perfectly isolated from us on Earth, and thus remain in a
superposition until the the several hours it takes for light to
get to Earth from Pluto reaches us?
?? Are you assuming that decoherence only occurs when humans (or
Earthlings) observe the event?
Brent
No, just that superposition is a relative, rather than objective notion.
OK. Welcome to QBism.
Brent
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