From: *Bruno Marchal* <[email protected] <mailto:[email protected]>>
On 12 Aug 2018, at 14:59, Bruce Kellett <[email protected]
<mailto:[email protected]>> wrote:
No, Price is wrong. He collapses the wave function in a non-local
manner, even though he doesn't seem to realize it. Let me try again.
The state is
|psi>= (|u>|d> - |d>|u>).
Let Alice interact with particle 1 at one end:
|Alice>|psi> = |Alice>|u>|d> - |Alice>|d>|u>
Alice interacts only with particle 1 (locally), so |Alice>|u>|d> -->
|Alice sees u>|u>|d>, and similarly for the other component.
Now Bob interacts with a different state. He does not see |psi> as
above, but rather
|Alice sees u>|u>|d>|Bob> - |Alice sees d>|d>}u>|Bob>
The, if Bob measures along the same axis, he gets down for Alice's
up, or up for Alice's down. If he measures at some different angle,
he gets the appropriate rotated results. But Bob NEVER sees the
original unaltered rotationally symmetric singlet state:
I have never disagreed with this. But Bob’s view is only a part of the
picture. Any particular Bob cannot see the symmetry; because it is
part of the symmetry.
But it is Bob's view here that is relevant to the formation of the
correlations. Bob measures that state he sees, not some phantom
symmetric state. Alice's measurement destroys the symmetry of the
singlet state -- it is not preserved magically in any many-worlds
picture. There is no 'outside view' in MWI as there is in your classical
M/W duplication thought experiments. There is no view where the symmetry
is preserved. Not even Tegmark's imaginary bird view preserves the
symmetry. You are mistaken here.
Alice's measurement (assuming Alice measures first in some frame)
collapses the state non-locally to affect the state that Bob sees.
That makes no sense to me.
Then you don't understand quantum mechanics.
Since the original state is non-separable, the fact that Alice has
interacted with it changes the whole state.
No measurement makes any change in any state, except local memories.
Even Bohr acknowledge this in his reply to EPR (but then get irrational).
Bohr did not really understand what Einstein was on about. He thought it
was determinism, whereas Einstein was always concerned about locality:
"No spooky action at a distance". But never mind Bohr or Einstein, the
measurement changes the state by destroying the original symmetry. The
singlet state is different from the conventional collapse picture used
to explain the formation of spots on the screen in the double slit
experiment. Everett removed the collapse in the double slit case, but he
did not remove it for the entangled state. Tell me, where in your
many-worlds picture is the measured singlet state still symmetrical?
This is the calculation as Price and Tipler give it, and this
calculation is clearly non-local.
It is non local, but does not involve any physical FTL or
instantaneous action at a distance. There would be some FTL in case
the collapse are real.
You are still obsessing about FTL. The collapse is instantaneous, but
there is no physical FTL. Maudlin finally got to understand this in his
2011 book. He adopts the relativistically covariant "flash GRW" idea for
the non-local collapse.
Going to the GHZ state will not change anything. What you have to do
is show how to re-interpret this calculation so that Bob sees the
original singlet AFTER Alice has measured her particle. I insist that
the original non-separability of the state makes any such
demonstration impossible.
I agree with this.
And even if it were possible, it would not reproduce the known
quantum correlations; the non-separability and the above non-local
reduction of the state is an essential part of quantum mechanics.
Nor with this.
Maybe you mean to say that you do *not* agree with the above?
Bruce
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