On 12/29/2013 2:01 PM, Jason Resch wrote:
On Sun, Dec 29, 2013 at 1:47 AM, meekerdb <meeke...@verizon.net
On 12/28/2013 6:41 PM, Jason Resch wrote:
On Sat, Dec 28, 2013 at 8:32 PM, meekerdb <meeke...@verizon.net
On 12/28/2013 4:45 PM, Jason Resch wrote:
On Sat, Dec 28, 2013 at 7:12 PM, meekerdb <meeke...@verizon.net
On 12/27/2013 10:31 PM, Jason Resch wrote:
To that I would add the purely epistemic "non-intepretation" of
"No interpretation needed" -- I can interpret this in two ways, one
is to just take the math and equations literally (this leads to
the other is "shut up and calculate", which leads no where really.
2. Determined by which observer? The cat is always either
or alive. It's just a matter of someone making a
So are you saying that before the measurement the cat is neither
alive nor dead, both alive and dead, or definitely alive or
definitely dead? If you, (and I think you are), saying that
is always definitely alive or definitely dead, then about about
radioactive atom? Is it ever in a state of being decayed and not
decayed? If you say no, it sounds like you are denying the
of the superposition, which some interpretations do, but then
leads to difficulties explaining how quantum computers work
require the superposition to exist).
Superposition is just a question of basis. An eigenstate in one
basis is a superposition in another.
Can you provide a concrete example where some system can
be considered to be both in a superposition and not? Is this like
superposition having collapsed for Wigner's friend while remaining
Wigner before he enters the room?
?? Every pure state can be written as a superposition of a complete
basis states - that's just Hilbert space math.
So then when is the system not in a superposition?
When it's an incoherent mixture of pure states.
What makes it incoherent though?
If the density matrix is not a projection operator, i.e. rho^2 =/= rho,
But really I just meant that in theory there is a basis in which any given
state is just (1,0,0,...). In theory there is a 'dead&alive' basis in which
Schrodinger's cat can be represented just like a spin-up state is a
a spin-left basis.
So if someone keeps alternating between measuring the spin on the y axis, and then the
spin on the x axis, are they not multiplying themselves continuously into diverging
states (under MWI)? Even though these states only weakly interfere, are they not still
superposed (that is, the particles involved in a simultaneous combination of possessing
many different states for their properties)?
Right, according to Everett, the world state becomes a superposition of states of the form
|x0,x1,...> where each xi is either +x, -x, +y, or -y. And per the Bucky Ball, Young's
slit experiment, the spins don't have to observed by anyone. If the silver atom just goes
thru the Stern-Gerlach apparatus and hits the laboratory wall, the superposition is still
created. If it just goes out the window and into space...it's not so clear.
An electron in a superposition, when measured, is still in a superposition
according to MWI. It is just that the person doing the measurement is now
caught up in that superposition.
The only thing that can destroy this superposition is to move everything
the same state it was originally for all the possible diverged states,
practically never happen for a superposition that has leaked into the
In Everett's interpretation a pure state can never evolve into a mixture
evolution is via a Hermitian operator, the Hamiltonian. Decoherence makes
submatrix corresponding to the system+instrument to approximate a mixture.
why it can be interpreted as giving classical probabilities.
Are there pure states in Everett's interpretation? Doesn't one have to consider the wave
function of the universe and consider it all the way into the past?
I suppose the universe could have started in a mixed state, but most cosmologists would
invoke Ockham and assume it started in a pure state - which, assuming only unitary
evolution, means it's still in a pure state. Of course since inflation there can be
entanglements across event horizons, so FAPP that creates mixed states.
In any case, returning to the original point that began this tangent, do agree that QM
interpretations which are anti-realist (or deny the reality of the superposition) are
unable to describe where the intermediate computations that produce the answer to a
quantum computation, take place?
They take place in a quantum computer.
What would Fuchs say about quantum computation?
It's a physical process whose outcome is predicted by QM.
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