From: *Bruno Marchal* <marc...@ulb.ac.be <mailto:marc...@ulb.ac.be>>
On 21 Aug 2018, at 02:20, Bruce Kellett <bhkell...@optusnet.com.au
<mailto:bhkell...@optusnet.com.au>> wrote:
From: *Bruno Marchal* <marc...@ulb.ac.be <mailto:marc...@ulb.ac.be>>
On 20 Aug 2018, at 13:18, Bruce Kellett <bhkell...@optusnet.com.au
<mailto:bhkell...@optusnet.com.au>> wrote:
You didn't respond to my earlier post in which I discussed the
symmetry breaking occasioned by Alice's measurement interaction
with the singlet state. I copy the relevant parts of my earlier
post here:
"The fact that Alice's interaction with the state is unitary and
can be reversed does not mean that the original symmetry still
exists in some sense. If I place a large weight at some point on
the circumference of a bicycle wheel, the rotational symmetry of
that wheel is lost. The fact that I can reverse the process by
removing the imposed weight does not mean that the altered wheel is
still rotationally symmetric in some wider view.”
OK, but when the heavy object is removed, at that moment, the
symmetry is back. Then, when Alice makes the measurement, the
symmetry is lost from her point of view, but the general symmetry of
the state has not changed. It is only not retrievable by Alice
(unless quantum erasure, amnesia, etc.).
Bruno, you have not made the least effort to understand the point I
made above,
Stop speculating on people.
I am merely responding to what you wrote. No speculation involved.
or to respond to it intelligently.
Sop making judgement.
There has been no intelligent response. No judgement involved.
It is difficult to believe that you are actually discussing this in
good faith. You just keep repeating your own misunderstandings of the
situation.
This is discussed since the beginning of QM. Stop talking like if only
you understand Everett.
Well, it does not appear as though you do either. You keep adding in
infinities of observers that are not part of Everett's formulation of QM.
The measurement that Alice makes destroys the symmetry. That is all
there is to it. There is not some wider symmetry that is preserved.
That is Bohr theory. Not Everett. A measurement does not change
anything in the big picture. It collapses wave and destroys symmetries
only in the relative first person mind associated to bodies doing the
experience.
It is not Bohr's theory, it is quantum mechanics. You appear to believe
that symmetry cannot be destroyed, even though I have given clear
examples where this happens. The symmetry is destroyed totally, not just
in the mind of the experimenter. If the symmetry is still preserved in
some bigger picture, it is up to you to prove this. But you have not
been able to do so. It is just an assertion on your part. And that
assertion happens to be false.
What you have to do is to work through the application of the
Schrödinger equation for this situation, without invoking any collapse,
and demonstrate that the symmetry is still present in the total wave
function. I contend that you will not be able to do this, because the
interaction with the singlet state destroys the rotational symmetry.
This is really a trivial observation since the Stern-Gerlach magnet
itself is not rotationally symmetric.
Bruce
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