On 8/1/2018 10:22 PM, Jason Resch wrote:
On Wed, Aug 1, 2018 at 11:34 PM Brent Meeker <[email protected]
<mailto:[email protected]>> wrote:
On 8/1/2018 3:46 PM, Jason Resch wrote:
On Wed, Aug 1, 2018 at 1:39 PM Brent Meeker <[email protected]
<mailto:[email protected]>> wrote:
On 8/1/2018 3:51 AM, Bruno Marchal wrote:
On 31 Jul 2018, at 21:46, Brent Meeker
<[email protected] <mailto:[email protected]>> wrote:
On 7/31/2018 9:11 AM, Bruno Marchal wrote:
On 30 Jul 2018, at 22:27, Brent Meeker
<[email protected] <mailto:[email protected]>> wrote:
On 7/30/2018 9:58 AM, John Clark wrote:
>
/Forget collapse./
Many, perhaps most, physicists do exactly that because
they believe in the "Shut Up And Calculate" quantum
interpretation and are only interested in predicting how
far to the right a indicator needle on a meter moves in
a particular experiment. But for some of us that feels
unsatisfying and would like to have a deeper
understanding about what's going on at the quantum level
and wonder why there is nothing in the mathematics that
says anything about a wave collapsing.
That's not true. "The mathematics" originally included
the Born rule as part of the axiomatic structure of QM.
In the usual QM, yes. But this use a vague notion of
observer, and a seemingly forbidden process, a projection
(a Kestrel!), I mean forbidden if we apply the wave to the
couple observer-particle.
Most of all they want to know what exactly is
a "measurement" and why it so mysterious.
The problem with the Born rule was that its application
was ambiguous:
Ah! Exactly.
Where was the Heisenberg cut? Why was "the needle basis"
preferred? But decoherence theory has given answers (at
least partially) to those questions. Given those
answers, one can just replace "collapse" with "discard",
i.e. discard all the predicted possible results except
the one observed. Is there really any difference between
saying those other predictions of the wf are in
orthogonal, inaccessible "worlds" and saying they just
didn't happen. That seems to be Omnes approach. He
writes, "Quantum mechanics is a probabilistic theory, so
it only predicts probabilities.”
OK, but the honest, and perhaps naive inquirer would like
to have an idea about what are those probabilities about,
and where they come from.
That was the source of resistance to Born's paper.
Physicists assumed that probability could only arise from
ignorance of an ensemble. Since there was no ensemble in
Heisenberg's (or Schroedinger's) QM they resisted the
idea. Lots of attempts were made to reintroduce ensembles,
or at least virtual ensembles, so that they could feel
comfortable with having a probabilistic theory. Omnes' is
just saying "Get over it!"; probabilities are fundamental.
Yes, but he said all this after defending Everett (or its
own better version of Everett). Then, this introduces a
notion of ensemble (the set of all consistent histories),
and, at least in some book, just ask us to be irrational and
to dismiss the ensemble at make probability fundamental,
only to make the “other worlds” disappear. In one book he
lakes clear that such a decision is irrational, and that he
makes it because he dislike of find shocking the idea that
all quantum possible outcome are realised. It is a bit like
a christian who understand the evolution theory, but add
that it makes just God having invented evolution instead of
Adam.
There's nothing irrational about discarding that which is not
observed and keeping that which is observed.
It is irrational if it results in a significantly more complex,
ad hoc, or nonsensical theory.
So it's irrational if it postulates infinitely many unobservable
worlds. Nothing is more sensible than discarding that which is
unobservable.
See, I can be just as snarky as you.
I was being serious. This explains my position well:
https://www.scientificamerican.com/article/multiverse-the-case-for-parallel-universe/
Remember: Parallel universes are not a theory—they are predictions
of certain theories.
To me, the key point is that if theories are scientific, then it's
legitimate science to work out and discuss all their consequences
even if they involve unobservable entities. For a theory to be
falsifiable, we need not be able to observe and test all its
predictions, merely at least one of them. My answer to (4) is
therefore that what's scientifically testable are our mathematical
theories, not necessarily their implications, and that this is
quite OK. For example, because Einstein's theory of general
relativity has successfully predicted many things that we can
observe, we also take seriously its predictions for things we
cannot observe, e.g., what happens inside black holes.
Likewise, if we're impressed by the successful predictions of
inflation or quantum mechanics so far, then we need to take
seriously also their other predictions, including the Level I and
Level III multiverse. George even mentions the possibility that
eternal inflation may one day be ruled out—to me, this is simply
an argument that eternal inflation is a scientific theory.
[...]
George also mentions that multiverses may fall foul of Occam's
razor by introducing unnecessary complications. As a theoretical
physicist, I judge the elegance and simplicity of a theory not by
its ontology, but by the elegance and simplicity of its
mathematical equations—and it's quite striking to me that the
mathematically simplest theories tend to give us multiverses. It's
proven remarkably hard to write down a theory which produces
exactly the universe we see and nothing more.
The theory that branches we don't observe don't exist is a needless
complication to the simplicity of QM, one not motivated by evidence,
LOL! It's absence from all observation is not evidence motivating it's
non-existence. The inclusion of infinitely many unobservable worlds is
"avoiding a needless complication". I'm sorry but you have not
convinced me you are serious.
and introduces all kinds of unintended baggage (priviledged reference
frames, magical observers, discontinuity, violations of unitarity, FTL
effects, perhaps even solipsism).
All invented and avoidable "flaws" which only in your mind are worse
than infinitely many worlds whose origin cannot be pinned down but we
are assured must exist because otherwise...horrors, non-unitarity might
obtain...and observation might be respected.
Brent
Jason
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