On 26-09-2019 21:38, 'Brent Meeker' via Everything List wrote:
On 9/26/2019 11:55 AM, smitra wrote:
On 26-09-2019 02:56, 'Brent Meeker' via Everything List wrote:
On 9/25/2019 2:28 PM, smitra wrote:
On 25-09-2019 15:30, Philip Thrift wrote:
On Wednesday, September 25, 2019 at 8:15:59 AM UTC-5, John Clark
wrote:
On Wed, Sep 25, 2019 at 9:11 AM Philip Thrift <cloud...@gmail.com>
wrote:
On Wednesday, September 25, 2019 at 6:54:59 AM UTC-5, John Clark
wrote:
It seems that nearly everyone on the list has a strong opinion
about
Sean Carroll's new book, but has anyone other than me actually
read
it?
John K Clark
_> He has posted several excepts (images of pages from the book)
on
Twitter and this excerpt_
https://lithub.com/if-you-existed-in-multiple-universes-how-would-you-act-in-this-one/
[1]
_and it's nothing new that I can see._
In other words the answer to my question is a resounding NO.
John K Clark
Maybe enlighten the world: What specifically in the book makes Many
Worlds compelling vs. the one-world alternatives? And if there is
nothing in the Many Worlds approach that is really better than a
one-world approach, why multiply worlds beyond necessity? And where
does all the extra matter come from to keep branching off new
worlds
again and again?
Seems like there should be some simply stated answers to these
questions.
I haven't read the book (yet) either, but the argument put forward
by Sean Carroll, Max Tegmark, David Deutsch, Lev Vaidman and many
others over the years, boils down to:
1) There is no hint from experiments of a violation of unitary time
evolution according to the Schrodinger equation.
Except every measurement ever made in every experiment ever run.
Measurement involves an interaction of the system with another system.
But we can do measurements to verify whether or not the system itself
when it is perfectly isolated evolves according to the Schrodinger
equation. No violation has ever been found.
Of course not. They would have to be found by measurement...which
requires the realization of a single world.
That measurement effectively collapses the wavefunction doesn't prevent
one from performing experiments to verify that no collapse happens in
the absence of interactions with external degrees of freedom. One can
e.g. do experiments using a quantum computer, apply a unitary transform
to a qubit and then apply the inverse of that transform and then measure
the state of the qubit. If the qubit's state had collapsed or interacted
with the environment, then the final state would be different from the
initial state and that van be detected.
2) People, equipment used to do measurements etc. consist of atoms
that are subject to the same laws of physics as everything else in
the universe.
Suppose, although I agree is hasn't been done, it could be shown that
QM predicts evolution into a mixed state. Wouldn't that show that is
simply a probabilistic theory and it predicts probabilities and
events
occur in accordance with those probabilities (as Omnes' writes).
Even a mixed state can be interpreted as a multiverse. But you could
then argue that the separate worlds are totally independent of each
other and that then gives room for a theory that says that only one of
the worlds is real. Because in QM you never get this situation, that's
strong evidence for the reality of the different worlds.
You can't cite a theory that says multiple worlds exist as evidence
for multiple worlds exist. That's strictly circular. What I'm
questioning is whether QM is correct. Zurek makes and argument that I
think, if worked out, would make the density matrix strictly diagonal.
If you approximate the environment as consisting of an infinite number
of degrees of freedom, then the different branches can decohere exactly.
Zurek's "envirance" argument becomes exact in this limit of an infinite
number of degrees of freedom. But since interactions are local and there
are only a finite number of physical degrees of freedom involved in the
interactions in a finite time, one cannot appeal to an exact
decoherence.
Saibal
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