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Re: [OM] New additions to the Living History Farm

Subject: Re: [OM] New additions to the Living History Farm
From: Mike Gordon via olympus <olympus@xxxxxxxxxxxxxxxxx>
Date: Wed, 9 Sep 2020 23:38:18 +0000 (UTC)
Cc: usher99@xxxxxxx
> Obviously you have not yet read the latest in science:
> https://www.sciencemag.org/news/2020/08/quantum-paradox-points-shaky-foundations-reality
> https://www.sciencealert.com/a-new-quantum-paradox-throws-the-foundations-of-observed-reality-into-question

AG says:

<<I'll stick with Einstein on this one.

Interesting articles but overinterpreted by the press as usual.  Quantum 
mechanics is weird enough w/o overinterpretation.  The "measurement problem" in 
QM really hasn't been resolved.     Wave fxn's collapse  when measured  and 
wave/particle duality of particles do as well--see the recent incarnation of 
that effect from the Weitzman Institute:


So the more efficient the detector of electrons the less interference pattern 
there is and the more the electrons behave as particles.  Don't watch--wave;  
watch particle.

This new  experiment interpreted as no objective reality exists is like a fancy 
Wigner's friend paradox.  It really just confirms Bell's inequality and c/w 
known QM.  The "measurers" are really photons assessing polarization and not a 
macroscopic device controlled by consciousness.  To call them Bob and Alice is 
misleading.  What I really  want to know is why such experiments are always run 
by Bob and Alice and not Poindexter and Cassandra?

I'll go with Sean Carroll at Cal Tech. ---see below:

"Reality Remains Intact
by Sean Carroll
Of course there is not a new experiment that suggests there’s no such thing as 
objective reality. That would be silly. (What would we be experimenting on?)

There is a long tradition in science journalism—and one must admit that the 
scientists themselves are fully culpable in keeping the tradition alive—of 
reporting on experiments that (1) verify exactly the predictions of quantum 
mechanics as they have been understood for decades, and (2) are nevertheless 
used to claim that a wholesale reimagining of our view of reality is called 
for. This weird situation comes about because neither journalists nor 
professional physicists have been taught, nor have they thought deeply about, 
the foundations of quantum mechanics. We therefore get situations like the 
present one, where an intrinsically interesting and impressive example of 
experimental virtuosity is saddled with a woefully misleading sales pitch.

My own preferred version of quantum mechanics is the Everett, or Many-Worlds 
formulation. It is a thoroughly realist theory, and is completely compatible 
with the experimental results obtained here. Thus, we have a proof by 
construction that this result cannot possibly imply that there is no objective 
reality. I am fairly confident that other realist approaches—hidden-variables 
models such as Bohmian mechanics, or dynamical-collapse models such as GRW 
theory—can offer equally satisfactory ways of interpreting this result without 
sacrificing objective reality, but I’m not confident in my ability to give such 
an account myself, so I’ll stick to the Everettian story.

Many-Worlds is a simple theory: there are wave functions, and they evolve 
smoothly according to the Schrödinger equation. Wave functions generally 
describe superpositions of what we think of as possible measurement outcomes, 
such as “horizontal” or “vertical” polarizations of a photon. The traditional 
“collapse of the wave function,” where an observer sees a unique measurement 
outcome, is replaced by decoherence and branching. That is, once a quantum 
superposition becomes entangled with a macroscopic system, that entanglement 
spreads to the environment (effectively irreversibly). If the measurement 
apparatus included a physical pointer indicating different possible results, 
that pointer cannot help but interact differently with the photons suffusing 
the room it’s in, depending on where it’s pointing. The pointer is now 
entangled with its environment.

That’s decoherence, and it implies that the two parts of the superposition now 
describe separate, non-interacting worlds, each of which includes observers who 
see some definite measurement outcome. The separate worlds aren’t put in by 
hand; they were always there in the space of all possible wave functions, and 
Schrödinger’s equation naturally brings them to life. If you believe a photon 
can be in a superposition, it’s not much of a conceptual leap to believe that 
the universe can be.

The experiment under question here is a version of Wigner’s Friend. The idea is 
to illustrate the possibility that observers in a quantum world can obtain 
measurement results, or “facts,” that are seemingly inconsistent with each 
other. One person, the “friend,” observes the polarization of a photon and 
obtains a result. But from the perspective of Wigner, both the photon and the 
friend appear to be in a superposition, and no measurement outcome has been 
obtained. How can we reconcile the truth of both perspectives while maining a 
belief in objective reality?

It’s pretty easy, from a Many-Worlds perspective. All we have to do is ask 
whether the original quantum superposition became entangled with the external 
environment, leading to decoherence and branching of the wave function. If it 
did, there are multiple copies of both Wigner and his friend. If it did not, 
it’s not really accurate to say that a measurement has taken place.

In the experiment being discussed, branching did not occur. Rather than having 
an actual human friend who observes the photon polarization—which would 
inevitably lead to decoherence and branching, because humans are gigantic 
macroscopic objects who can’t help but interact with the environment around 
them—the “observer” in this case is just a single photon. For an Everettian, 
this means that there is still just one branch of the wave function all along. 
The idea that “the observer sees a definite outcome” is replaced by “one photon 
becomes entangled with another photon,” which is a perfectly reversible 
process. Reality, which to an Everettian is isomorphic to a wave function, 
remains perfectly intact.

Recent years have seen an astonishing increase in the precision and cleverness 
of experiments probing heretofore unobserved quantum phenomena. These 
experiments have both illustrated the counterintuitive nature of the quantum 
world, and begun to blaze a trail to a new generation of quantum technologies, 
from computers to cryptography. What they have not done is to call into 
question the existence of an objective reality. Such a reality may or may not 
exist (I think it does), but experiments that return results compatible with 
the standard predictions of quantum mechanics cannot possibly overturn it."

Stay calm, objective reality remains, Mike

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