Bell's Theorem basic question on contextuality & locality

In summary, the conversation discusses the concept of Bell's Theorem and its implications for the existence of particles before measurement. The main points are that Bell's Theorem shows that there are no hidden variables in quantum mechanics and that particles do not exist before measurement. There is also a mention of the differing views of two Physicsforums users, Neumaier and Bhobba, on the classical nature of physics and determinism in relation to Bell's Theorem. The conversation ends with the realization that the discussion is based on a misunderstanding and the thread is closed.
  • #1
jlcd
274
7
I'm familiar with Bell's Theorem.. have studied it over the years. I'd just like to confirm if my belief is correct. In short. It shows either particles don't exist before measurement or there are hidden variables.. you know all those non-counterfactual and locality arguments.. Specker theorem etc. I know them. But I got confused lately when hbobba can't seem to understand what I'm saying.

So let me repeat. If you don't believe in non-local influence. Then particles don't exist before measurement correct? I tend to believe in the latter.. but is it right thing to say particles don't exist before measurement? What is the right words to say if it is not semantically correct?

Whatever, the essence is still particles don't exist before measurements.

In Physicsforums. the Copenhagen camps (note Ensemble is still cousin to Copenhagen) which is believed by Bill Hobba and company. They keep on saying it is all classical reality with only statistics or probability and it's what QM (and even QFT) is all about. But isn't it EPR shows it is not all classical reality? And particles don't really exist before measurements? Since hbobba believes particles exist before measurement (since this is what Newtonian classical world is all about). How does he or others view EPR.. there are non-local influence or everything is deterministic? Just like Neumaier, hbobba is incredibly advanced mathematically that they can no longer communicate well with beginners without using dense math. So hope others can explain in English. Thank you.
 
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  • #2
jlcd said:
I'm familiar with Bell's Theorem.. have studied it over the years. I'd just like to confirm if my belief is correct. In short. It shows either particles don't exist before measurement or there are hidden variables

The point of Bell's theorem is to show that there AREN'T any hidden variables, or at least not if all interactions are local (propagate at lightspeed or slower).
 
  • #3
stevendaryl said:
The point of Bell's theorem is to show that there AREN'T any hidden variables, or at least not if all interactions are local (propagate at lightspeed or slower).

So it's either non-local hidden variables or particles don't exist before measurement. Bohr believes the latter where its part of the experimental setup even if they are located light years away. So is it accurate to say particles don't exist before measurement if you don't believe in non-local hidden variables?
 
  • #4
I guess the "semantically correct" expression would be the particles' status is undefined, or their properties are undefined. To say they don't exist is already saying something definite (like in their place is a vacuum state or something), which is wrong.
 
  • #5
ddd123 said:
I guess the "semantically correct" expression would be the particles' status is undefined, or their properties are undefined. To say they don't exist is already saying something definite (like in their place is a vacuum state or something), which is wrong.

Ok. I can't fully understand Neumaier present long thread of it with very dense math. I know he believes in classical reality. So does he believe in non-local influence or hidden variables or no-go theorem regarding EPR and bell's theorem? Can anyone summarize his view with simple english? How does the distant correlations work in Neumaier view? determinism? hidden variables? non-local influence.. how can he make it classical?
 
  • #6
I understood the opposite, that Neumaier doesn't really think the world is classical, just that classical analogues can be made to make QM look not weird. In the end I'll just disagree until he comes up with a serious explanation of EPR.

Nor does Bhobba think physics is classical, just that the whole point of QM is continuous transformations between pure states which, even though it's surely not a classical concept, for him it is intuitive. For me it's not. A difference between Neumaier and Bhobba is that the former believes in determinism and the latter doesn't.

So that's my breakdown on these PF's two users, for whatever reason you needed that.
 
  • #7
jlcd said:
'd just like to confirm if my belief is correct. In short. It shows either particles don't exist before measurement or there are hidden variables.

That belief is completely incorrect. Bell's theorem shows that no local hidden variable theory can reproduce all the predictions of quantum mechanics.

As this thread is based on a misunderstanding, there is no point in continuing the discussion and the thread is closed.
 

What is Bell's Theorem and why is it significant?

Bell's Theorem is a fundamental concept in quantum mechanics that addresses the relationship between contextuality and locality. It states that no physical theory can reproduce all the predictions of quantum mechanics while simultaneously satisfying the requirements of contextuality and locality. This means that quantum mechanics cannot be explained by a theory that is both contextual and local, making it a crucial principle in understanding the fundamental laws of nature.

What is the difference between contextuality and locality?

Contextuality refers to the idea that the measurement of a quantum system can be influenced by the context in which it is measured, while locality refers to the principle that the properties of a system are determined by its local environment and cannot be influenced by distant events. Bell's Theorem explores the relationship between these two concepts and how they relate to the predictions of quantum mechanics.

How was Bell's Theorem proven experimentally?

Bell's Theorem was first proposed by physicist John Stewart Bell in 1964, but it was not until 1982 that the first experimental confirmation was achieved by Alain Aspect and his team. They conducted a series of experiments using entangled photons to test the predictions of Bell's Theorem and found that the results were in agreement with the theory, providing strong evidence for the validity of the theorem.

What are the implications of Bell's Theorem for our understanding of reality?

Bell's Theorem has significant implications for our understanding of reality and the fundamental laws of nature. It suggests that there are inherent non-local connections between quantum systems, challenging our traditional understanding of causality and determinism. It also raises questions about the nature of reality and the role of measurement in shaping our observations of the world.

How is Bell's Theorem relevant to current research in quantum mechanics?

Bell's Theorem continues to be a topic of intense research in the field of quantum mechanics. It has been used to explore the foundations of quantum theory, as well as to develop new technologies such as quantum cryptography and quantum computing. It is also being studied in the context of quantum entanglement and the potential for long-distance communication and teleportation.

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