Nerd alert! -more spooky Quantum stuff

[polymath257]

"Why" is a question that has little relevance in the sciences, which are used to describe "how" things work, to as close an approximation as we can measure. Science isn't the correct venue for "why" questions.

Which is why our man Einstein said those immortal words. (spooky action at a distance)
But he was wrong by arguing the moon doesn't disappear when we're not looking at it, and God doesn't play dice. (response to Bohr)
Even he was conflating the macro world (Newtonian) with the quantum world. The "why" played havoc on his mind.

Einstein was demonstrably wrong about what happens to entangled particles. He thought that the EPR paradox showed something that could not be the case in reality. And yet, we have done experiments that show *exactly* that phenomenon does happen and in a way consistent with QM.

---

I agree with Einstein that God does not play dice.

It is said that there are no hidden variables. But to me that is just science working within its own framework and not making statements outside itself. As it shouldn't.

The truth is that absence of evidence is not evidence of absence. And that in response to "there are no hidden variables", when wrongly taken as a truth beyond the scope of science, I would simply ask: how would we know?

We know because of the violation of Bell's inequalities. ANY hidden variable theory that is local and realist obeys those inequalities. But, by actual observation, the universe does not.

Einstein was wrong: the universe is inherently probabilistic at base.

Quantum deterministic causation that is far too complex to be examinable by us is indistinguishable from quantum acausality.

Scientific theories simply don't make statements outside their scope ... if something is unfalsifiable science doesn't claim to have absolute knowledge that the unfalsifiable thing is impossible---science just says it isn't real *in scientific terms*. But that's only one way of saying it. Other scientists would say that it isn't knowable by science but still may or may not be real. It depends. As there are scientists who are scientific pragmatists who believe in methodological scientific realism but don't believe in metaphysical scientific realism---they believe that science deals with knowledge of reality rather than with reality itself.

What's more, there are also deterministic models of quantum mechanics too. Not all quantum physicists would agree that God does not play dice (metaphorically speaking). I believe that the model of QM that Sean Carroll holds to is, if I'm not mistaken, a deterministic one.

The problem with those deterministic models (Bohmian mechanics) is that they only work for classical quantum theory. Once you go to the special relativistic side (quantum field theories), they fail miserably. So, effects like spin and anti-matter are not explained by such theories.

Also, Bohmian mechanics violates the 'local' aspect: there is faster then light signaling, which in a relativistic situation means reverse-time causality.

Also, there is a difference between actual literal indeterminism and acausality on the one hand and indeterminism in the sense of indeterminancy, or in other words, unpredictability and acausality to mean science's inability to find any causes at the quantum level, on the other hand.

To me it's just an error of mistaking the map for the territory. Science is a map rather than a territory. But it's not just a map. It's the best map we have! By far. But it's still a map.

Agreed, but we can, and have, eliminated a whole class of hidden variable theories (those that are both local and realist) because of the failure of Bell's inequalities.

That means, ultimately, that any hidden variable model has to have attributes even stranger than quantum mechanics.

---

By "observer", some concluded, fallaciously, that it meant "conscious" observer.

There's no such thing as a non-conscious observer. So either it's not really an observer at all or it's a conscious observer.

A Geiger counter is enough to 'collapse the wave function', but is not usually regarded as being conscious. The *vast* majority of modern measurements are not done by conscious observers.

---

So. We agree with "Any interaction counts as an 'Observation'." ? Cool.

Perhaps in one sense. Perhaps in both senses. But my point is that at least one sense of observation requires consciousness and that was the sort of observation I was interested in.

My own belief is that everything requires conscious observation in some form.

And that belief is wrong when it comes to issues of wave function collapse in quantum mechanics.

Technically, what is required is an 'irreversible interaction'. It is the irreversibility that 'collapses the wave function'. Furthermore, this type of irreversibility can happen by interaction with almost any macroscopic object (and even many microscopic ones).

This whole aspect was elucidated in the 1990's under the name of 'decoherence theory' and has been verified by observation. For example, maintaining coherence is one of the big challenges in making quantum computers: *any* significant interaction tends to collapse the wave function and destroy the calculation.

[GrandizerII]

What's more, there are also deterministic models of quantum mechanics too. Not all quantum physicists would agree that God does not play dice (metaphorically speaking). I believe that the model of QM that Sean Carroll holds to is, if I'm not mistaken, a deterministic one.

The problem with those deterministic models (Bohmian mechanics) is that they only work for classical quantum theory. Once you go to the special relativistic side (quantum field theories), they fail miserably. So, effects like spin and anti-matter are not explained by such theories.

Also, Bohmian mechanics violates the 'local' aspect: there is faster then light signaling, which in a relativistic situation means reverse-time causality.

What about Many-Worlds Interpretation? Which is what Sean Carroll believes is the correct one (not Bohm's interpretation).

[polymath257]

The problem with those deterministic models (Bohmian mechanics) is that they only work for classical quantum theory. Once you go to the special relativistic side (quantum field theories), they fail miserably. So, effects like spin and anti-matter are not explained by such theories.

Also, Bohmian mechanics violates the 'local' aspect: there is faster then light signaling, which in a relativistic situation means reverse-time causality.

What about Many-Worlds Interpretation? Which is what Sean Carroll believes is the correct one (not Bohm's interpretation).

Well, the Everette interpretation also isn't deterministic. There's no way to know which way the world will split for you. It has the advantage of taking the Schrodinger equation seriously, but so does decoherence.

[GrandizerII]

What about Many-Worlds Interpretation? Which is what Sean Carroll believes is the correct one (not Bohm's interpretation).

Well, the Everette interpretation also isn't deterministic. There's no way to know which way the world will split for you. It has the advantage of taking the Schrodinger equation seriously, but so does decoherence.

Ontologically, it is deterministic, though, right? That's what I remember Sean Carroll saying (if I do remember correctly).

[HappySkeptic]

What about Many-Worlds Interpretation? Which is what Sean Carroll believes is the correct one (not Bohm's interpretation).

Well, the Everette interpretation also isn't deterministic. There's no way to know which way the world will split for you. It has the advantage of taking the Schrodinger equation seriously, but so does decoherence.

I do not like Many-Worlds, and I don't know why some top physicists do.  I know Lee Smolin hates it too.  His idea is many potential realities within one universe, not one reality each in an infinite number of splitting universes.  I agree.

As for decoherence theory -- it is clearly correct, but it is not a QM interpretation (it can be included in any interpretation).  Decoherence theory does not provide for wavefunction collapse.  You still need an interpretation to explain collapse.

For those other readers that aren't familiar, decoherence theory states that each quantum interaction causes a new superposition.  After a particle has interacted with many other non-correlated particles, a measurement (which is just another superposition) of the original particle will be seen to experience a phase noise.  In QM terms, it diagonalizes the Hamiltonian, making a measurement of that particle appear classical instead of quantum.  However, there never is anything classical -- its quantum all the way down.  This "all the way down" is a problem, though, when applied to the entire universe.  It means there are infinite histories, and none ever really get chosen.  This isn't the universe we live in, so some sort of collapse must occur.

Now, it could be some self-collapse model involving wavefunction non-linearity (likely unworkable, as it violates energy conservation), or some sort of interaction with Gravity (from Penrose). 

I have seen apparent-collapse models (Montevideo interpretation) which allow for multiple realities, but when multiple particles share more and more information, the realities "for them" converge.  Reality is defined by the information relationships (what does one ensemble of particles "know" about another), not by a single absolute reality.  It fits very well with decoherence theory.  I like that one, but it hasn't attracted many followers.

[GrandizerII]

Many worlds is very neat and very sufficient and doesn't have to add some extra assumptions that other interpretations have to do. Though it does posit a lot of worlds but so what? When did we ever let counterintuitive be a problem for us?

You say we need to explain collapse, but isn't that sort of begging the question here? Why must there be a collapse at all? Incredulity isn't a good objection here.

ETA: Ok, rereading your post, perhaps charging you with begging the question was premature. Your argument for collapse is that there can't be an infinite regress or our universe would not be realized or something? I'm not sure why this should be the case. Under the MW interpretation, the waveform exists and all possibilities are realized in the form of worlds instead of just one. Not seeing the problem here. Maybe because I'm seeing it in an atemporal sense rather than temporal.

[HappySkeptic]

Many worlds is very neat and very sufficient and doesn't have to add some extra assumptions that other interpretations have to do. Though it does posit a lot of worlds but so what? When did we ever let counterintuitive be a problem for us?

You say we need to explain collapse, but isn't that sort of begging the question here? Why must there be a collapse at all? Incredulity isn't a good objection here.

ETA: Ok, rereading your post, perhaps charging you with begging the question was premature. Your argument for collapse is that there can't be an infinite regress or our universe would not be realized or something? I'm not sure why this should be the case. Under the MW interpretation, the waveform exists and all possibilities are realized in the form of worlds instead of just one. Not seeing the problem here. Maybe because I'm seeing it in an atemporal sense rather than temporal.

The Many Worlds Interpretation (MWI) has undergone a lot of changes.  Many of the originals did have a type of collapse -- the bifurcation of universes.  It was explained that such a bifurcation is a gradual process involving decoherence.  But, decoherence never fully translates to the classical situation.  While the Copenhagen Interpretation would just say "at some time after decoherence, we have collapse", MWI is saying the same thing "at some time after decoherence, we have a split universe".

In the sense that modern MWI tries to not have any form of collapse, I don't see them as fundamentally different than apparent collapse theories like Montevideo.  I'm not sure either of them truly work, however.

Both have to "trim down" the alternate histories.  MWI does it by postulating that all the other histories exist, just not in your universe (except perhaps with some vestige of correlation to the other universes).  Something like Montevideo suggest that the other histories get less and less probable as information is shared among observers, but they always have a vestige of existence that might be seen for some observers.

There is probably no difference.  One world with multiple histories, or many worlds with (mostly) one history.  It is probably identical.  But if either had truly solved the "collapse" problem, we would've declared the problem solved.  If you don't have Copenhagen collapse, you still find that all those "vestiges" of correlation between the alternate histories add up, when applied to the entire universe.

[Apollo]

Delayed choice quantum eraser!
My mind was blown before I even watched it!

Sean Carroll explains this isn’t so here:

https://www.preposterousuniverse.com/blo...um-eraser/

[The Valkyrie]

I'm surrounded by nerds!

[polymath257]

I'm surrounded by nerds!

Lucky you!