On 11/18/2024 5:53 AM, John Clark wrote:
On Sun, Nov 17, 2024 at 6:06 PM Bruce Kellett <[email protected]>
wrote
/> One of the frequently stated arguments for many worlds is that
it avoids the problem of the wave function collapse. The collapse
of the wave function is only a problem if the wave function is a
physical object,/
*Even if you assume, as Copenhagen does, that the quantum wave
function is just a prediction device and not a "real physical object"
you still have a grave problem; at exactly what point are you supposed
to stop trusting what that prediction device is telling you?
Copenhagen would answer that you should stop trusting it at the exact
point you make a measurement. Physics is the most precise of all the
sciences so it would be reasonable to then ask for the exact meaning
of this word "measurement", but when you do Niels Bohr and his friends
will respond with bafflegab, which I can only interpret as "shut up
and calculate". *
*By the way, the integers are not physical objects and neither is the
concept of "fast", does that mean that both are unreal? If so, how
would things be different if both of those things _WERE_ real? I
believe that if the wave function didn't lead to conclusions that make
some people, perhaps most people, uncomfortable, like there being many
other versions of themselvesin a multiverse, nobody would be insisting
that the wave function is not real. Physicists whose primary focus is
physics at its most fundamental level sure seem to behave as if they
thought it's real because they spend about 95% of their time studying
quantum field theory. *
/> because then you run into problems with instantaneous action at
a distance or FTL physical action./
*That's no problem in Many Worlds because you can say the split
happens instantaneously or you can say the split propagates at the
speed of light, it makes no difference because they both produce
identical observable results. *
/> If the wave function is purely epistemic, namely, nothing more
than a summary of our knowledge about the physical system, there
is no problem with collapse, because the result of an experiment
merely updates our knowledge, and the wave function is updated to
reflect this change in knowledge. /
*That's theBayesian interpretationand if you use that you will always
get the correct answer in your experiments. The exact same thing is
true with Shut Up And Calculate. I**f you don't care what's going on
and you're only interested in predicting if the needle on your
voltmeter will point to 3 or to 4 then I have absolutely no problem
with you using either, in fact I think the two ideas are identical,
they just have different names. *
/> This is exactly what happens in classical probability./
*Not quite.Nobody needed an interpretation of classical physics,
nobody needed a definition of "measurement" or "observer" because
regardless of the old cliché about a watched pot never boiling, the
time it takes to boil a pot of water really doesn't change depending
on if you are watching it or not, but in the weird quantum world you
really CAN delay the decay of a radioactive atom if you watch it
closely enough, and Many Worlds has no problem explaining how this
"Quantum Zeno Effect" works. *
*
*
*Suppose an atom has a half-life of one second and I'm watching it,
the universe splits and so do I after one second. In one universe the
atom decays and I observed that the atom has decayed, in the other
universe the atom has not decayed and I observed that it has not
decayed. *
*
*
*In the universe where the atom didn't decay after another second the
universe splits again, and again in one universe it decays but in the
other it has not, it survived for 2 full seconds. So there will be a
version of me that observes this atom, which has a one second
half-life, surviving for 3 seconds, and 4 seconds, and 5 years, and 6
centuries, and you name it. By utilizing a series of increasingly
complex and difficult procedures it is possible for the lab (and you)
to be in the universe that contains labs and versions of you that see
the atom surviving for an arbitrarily long length of time. But the
longer the time past its half-life the more splits are involved, and
the more difficult the experiment becomes.**Soon it becomes
ridiculously impractical to go further, but it's not impossible.*
*Quantum Zeno effect* <https://en.wikipedia.org/wiki/Quantum_Zeno_effect>
/> If the wave function is purely epistemic, there is no problem
with collapse, and the additional worlds that MWI introduces play
no useful role and can readily be discarded./
*The useful role that Many Worlds provides is that it doesn't need to
explain what a "measurement" or an "observer" is*
LOL. You just wrote three paragraphs immediately above each of which
referred to "observed". So if it doesn't need an explanation it must be
obvious and have the same meaning as in the neo-Copenhagen
interpretation, NCI. MWI needs to explain how and when the worlds
split, presumably due to decoherence although I've not seen an explicit
calculation of an instance of the process. The same when and how is
available to NCI if you think it needs one.
*, nor does it need to explain exactly, or even approximately, where
the Heisenberg cut is. *
No, it just assumes there is a point at which the world becomes multiple
and measurement is complete.
Brent
*And it doesn't need to explain what consciousness is because it has
nothing to do with it. *
*John K Clark See what's on my new list at Extropolis
<https://groups.google.com/g/extropolis>*
zeq
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