Undergrad The mechanism of entangled particles

[Derek P]

Is the measurement problem in essence not a 'history-selection-problem'?

It is, but there are so many completely different ways the selection could occur that lumping them all together is not really helpful. And, of course, interpretations such as MWI take the selection out of the realm of physics - there isn't any selection - and make it something akin to the anthropic principle. We see the state that we are part of.

 

[Mentz114]

I am curious as to the "other" reason to dismiss macroscopic superposition.

Superposition depends on the linearity of the WF. There is good reason (theoretically) to believe that linearity fails at high enough energies.
It is based on this paper

Schrödinger equation revisited
Authors : Wolfgang P. Schleich, Daniel M. Greenberger, Donald H. Kobe, and Marlan O. Scully

This is off-topic so if you want to discuss - please start a new thread.

 

[PeterDonis]

This is off-topic so if you want to discuss - please start a new thread.

New thread is here:

https://www.physicsforums.com/threads/is-non-linear-quantum-mechanics-even-plausible.942330/

 

[StevieTNZ]

It's probably better not to quote material that is 79 years out of date when the entire paradigm has been overhauled several times since then.

The reference provided by the honourable member is certainly not unworthy to be cited, as it is still relevant (at least in my opinion).

 

[Lord Jestocost]

Physics deals with the physical side of the observer, not with any subjective experience that the observer may or may not have. So in physics the observer is exactly the same as all the other subsystems...

That’s your point of view and that’s o.k. Why not? But others have different points of view. Let’s cite, for example, Erwin Schrödinger:

“One can only help oneself through something like the following emergency decree: Quantum mechanics forbids statements about what really exists – statements about the object. Its statements deal only with the object-subject relation. Although this holds, after all, for any description of nature, it evidently holds in a much more radical and far reaching sense in quantum mechanics.”

— Erwin Schrödinger, 1931, letter to Arnold Sommerfeld

 

[Lord Jestocost]

Making the observer fundamentally different from the rest of the universe is the second biggest source of confusion in quantum physics.

To my mind, the “artificial” split between object and conscious subject seems to be the source for the ongoing confusion when reasoning about quantum mechanics. As long as one insists on thinking about quantum phenomena with classical ideas (objective physical reality etc.) one will always run into dead ends. That we are conscious, self-knowing beings, we know for sure; no pointer readings are necessary to infer this fact. The rest of the universe? Who knows?

 

[bhobba]

As long as one insists on thinking about quantum phenomena with classical ideas (objective physical reality etc.) one will always run into dead ends. That we are conscious, self-knowing beings, we know for sure; no pointer readings are necessary to infer this fact. The rest of the universe? Who knows?

As I have mentioned before about your view of QM I think Dirac would be proud. Even I don't go quite that far - but we are getting off topic - you are of course correct - my view, just as an example, does make assumptions about the consciousness external world split that QM really says nothing about.

But regarding the measurement question here is some technicalities about measurement theory in its more modern form:
http://www.quantum.umb.edu/Jacobs/QMT/QMT_Chapter1.pdf

The title of the thread can be answered very easily buy just using the superposition principle on combined systems. You have two systems that can be in state |a> or |b>. If system 1 is in state |a> and system 2 in |b> that is written as |a>|b>. If system 1 is in state |b> and system 2 in state |a> that is written as state |b>|a>. But the principle of superposition says given any two states they can be in a superposition ie ci*|a>|b> + c2*b>|a>. Such systems are said to be entangled which is a peculiar kind of non-classical situation.

Thanks
Bill

 

[entropy1]

The title of the thread can be answered very easily buy just using the superposition principle on combined systems. You have two systems that can be in state |a> or |b>. If system 1 is in state |a> and system 2 in |b> that is written as |a>|b>. If system 1 is in state |b> and system 2 in state |a> that is written as state |b>|a>. But the principle of superposition says given any two states they can be in a superposition ie ci*|a>|b> + c2*b>|a>. Such systems are said to be entangled which is a peculiar kind of non-classical situation.

Is it the principle of superposition that makes entanglement possible, bhobba? (together with product states)

A product state seems to set a relation between Alice and Bob as to per decree: $|a \rangle |b \rangle$ says that if Alice measures $|a \rangle$, Bob measures $|b \rangle$, which is like setting a non-local relation condition, it seems to me. If this is physically real, non-locality is physically real, right? And if non-locality is not physically real, do we have right to declare non-locality in our math via the product state?

 

[bhobba]

Is it the principle of superposition that makes entanglement possible, bhobba? (together with product states)

Yes. Strictly speaking though it's a separate axiom.

A product state seems to set a relation between Alice and Bob as to per decree: $|a \rangle |b \rangle$ says that if Alice measures $|a \rangle$, Bob measures $|b \rangle$, which is like setting a non-local relation condition, it seems to me. If this is physically real, non-locality is physically real, right? And if non-locality is not physically real, do we have right to declare non-locality in our math via the product state?

Please rephrase - physically real is not a useful concept in physics because you can't define it - in relation to Bell contextual is a better word.

I have explained it many times - its simply an unusual relation two systems can have with statistical properties not the same as normal probability theory.

Thanks
Bill