On 8/1/2018 4:49 AM, Bruno Marchal wrote:
On 1 Aug 2018, at 07:49, Brent Meeker <meeke...@verizon.net
<mailto:meeke...@verizon.net>> wrote:
On 7/31/2018 10:19 PM, Jason Resch wrote:
On Tue, Jul 31, 2018 at 4:52 PM Brent Meeker <meeke...@verizon.net
<mailto:meeke...@verizon.net>> wrote:
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.
After reading the wiki article on QBism I still can't say I
understand what it is about, as it doesn't seem to offer any core
positions.
I am an adherent of bayesianism, and believe it applies generally in
all domains (being an agent having to make decisions/bets), so what
does QBism add if one already accepts a general reliance on Bayes
theorem? It doesn't seem like QBism takes any strong position on
any of the quantum paradoxes, nor offer any insights to addressing
or explaining them. In this it seems like a pretty empty theory,
with hints towards the "instrumentalist" and "shut up and calculate"
mindsets--that only the probability matters. To the extent that is
true, I reject QBism. While QBism might not put forward anything
that is false, the attitude it conveys seems like it would stymie
progress towards advancing our understanding of reality.
QBism says that QM is a theory for predicting personal beliefs. The
"collapse" of the wave function is simply updating one's beliefs
based on an observation.
That leads to the many-worlds, or its "many-minds” variants (even
closer to what mechanism enforce on the interpretation of the
observable). ITSTM.
There are many-minds who just happen to have (in many cases) different
information about the world and so use different states or Hamiltonians
to predict what they will observe. But the evidence is that there is
only one world.
Brent
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