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4
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1answer
306 views

Tracking down the locality assumption in a CHSH inequality derivation

CHSH inequality requires both locality and realism. I will equate here realism with counterfactual definiteness. Now counterfactual definiteness tells us that given two different measurements on the ...
2
votes
2answers
253 views

Determinism loophole?

I was thinking about the question I posted yesterday, and I thought of a better way to ask it. I'm trying to figure out why QM necessitates "pure randomness". Assume you have a photon that has a ...
0
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0answers
38 views

What does Bell's Theorem really violate? [duplicate]

Well this is a fairly straightforward question. I know it states that either hidden variables is wrong or Quantum Mechanics. But indirectly hidden variables is a part of QM due to uncertainty. So what ...
21
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5answers
2k views

Is Stephen Wolfram's NKS, an attempt to explain the universe with cellular automata, in conflict with Bell's Theorem?

Stephen Wolfram's A New Kind of Science (NKS) hit the bookstores in 2002 with maximum hype. His thesis is that the laws of physics can be generated by various cellular automata--simple programs ...
0
votes
3answers
60 views

“Spooky action at a distance” or particle correlation at the time of their creation?

In Bell test experiments, two particles that are a singlet are measured and are found to be correlated. The correlation leads us to believe that they are somehow connected non-locally: the ...
2
votes
1answer
100 views

(thought) experiment re: Bell's Theorem and Schrodinger's cat

I apologize if this question is naive. I am wondering about what would happen with the following experiment. Start with a standard Bell's Theorem setup: We have two quibits entangled in a particular ...
2
votes
1answer
168 views

Generalizations of Bell's inequality to quantum field theory

Can anyone refer me to some sources on generalizations of Bell's inequalities to quantum field theory (as opposed to quantum mechanics)? Scalar fields would be enough.
-1
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2answers
241 views

Does this Bell's experiment actually disprove Local Hidden Variable Theories (LHVT)

I'm watching some archived video lectures on QM in Coursera given by Umesh Vazirani from UC Berkeley and I have a question regarding a Bell's experiment (I guess something close to this) described in ...
0
votes
1answer
102 views

Non-locality and Bell's theory

Non-Locality – (just ) one more question? I have read comments that Bell’s theory proves quantum mechanics is non-local, and also comments that it does not. I have read a comment by a very eminent ...
2
votes
1answer
104 views

Has Bell really demonstrated that no local hidden variable theory can exist in his original paper of 1964? Why then verify the CHSH violation?

The more I read about it and the more I'm convinced I haven't understood what I thought I had. In the original paper ...
3
votes
2answers
249 views

Pauli matrices as measurement operators

I am trying to understand a paper on the Bell test experiments. I understand that if we wanted to measure the spin of a spin-1/2 particle in state $\psi$ along the z-axis we would apply the operator ...
0
votes
1answer
30 views

Where does the CSHS inequality really come from

I'm reading about Bell's inequalities and hidden variables theory. And I wonder where does the CSHS inequality really come from ? I read the paper and the inequality we find is ...
1
vote
1answer
75 views

Question on expression in “J.S.Bell : On the Einstein Podolsky Rosen paradox”

I have a question on the article J. S. Bell, On the Einstein Podolsky Rosen paradox, Physics 1, 195, 1964. (link) My question concerns the expression (3) of the ...
3
votes
1answer
126 views

On Bell inequality and bound entangled states

I have recently seen some presentation slides of Michał Horodecki (slide number 77) in which he discussed the following conjecture. Bound entangled states satisfy all Bell inequalities The ...
2
votes
5answers
288 views

How do we know that there isn't a classical solution to the measurement problem/Quantum Mechanical uncertainty?

It was mentioned to me that it can be shown that there is no classical explanation for the uncertainty in Quantum Mechanics -- i.e. that there are no hidden workings that we have just not yet seen, ...
3
votes
4answers
423 views

How do we show that no hidden variable theories can replace QM?

I've always hit two big stumbling blocks in conceiving of the proof or disproof of hidden variable theories as being even valid idea, let alone an answerable question... I feel I must be ...
2
votes
1answer
207 views

Measuring Entangled Qubits

Suppose we have a pair of entangled qubits. $$ |\psi\rangle = \frac{1}{ \sqrt{2} } ( |00\rangle + |11\rangle ) $$ Now we give one qubit to Alice and other to Bob. Alice measure the her qubit to ...
0
votes
1answer
61 views

Why Quantum correlation is not uniform in this diagram?

Following diagram is from a Wikipedia article which shows Quantum Correlation for local hidden variables and Quantum Mechanics and experiments confirm Quantum Mechanics predictions. My question is ...
2
votes
2answers
69 views

Is it possible to determine the state or values of something without measuring it

To give context to this question, I am currently looking into non-locality / hidden variables / Bell's Theorem, EPR / etc. I've noticed the assertion that the values / state of something when ...
5
votes
2answers
176 views

Bell's Theorem graph

My friends and I got into an argument about determinism, and I brought up that quantum events are random. But I couldn't prove it. I found the Wikipedia page on Bell's theorem, which seems to imply ...
0
votes
2answers
120 views

EPR vs. EPRBB? Why can't we perform the original EPR experiment?

The EPR gedanken experiment was invented by Einstein Podolsky and Rosen in 1935. It involved positions and momenta. In 1957, Bohm revised this gedanken experiment into one involving spins, or ...
2
votes
2answers
269 views

What are the “loopholes” in past Bell's theorem experiments?

I am intrigued by the following Phys.org article: Researchers began using photons in 1980s to test Bell's theory and determine if Einstein's reasoning is right or wrong. Since then, researchers ...
14
votes
5answers
960 views

What combinations of realism, non-locality, and contextuality are ruled out in quantum theory?

Bell's inequality theorem, along with experimental evidence, shows that we cannot have both realism and locality. While I don't fully understand it, Leggett's inequality takes this a step further and ...
6
votes
3answers
778 views

How does Bell's theorem rule out the possibility of local hidden variables?

It seems to be common consensus that the world is non-deterministic and this is proved by Bell's theorem. But even though Bell's experiments proved that the theory of quantum mechanics work, How does ...
6
votes
1answer
92 views

States diagonal in the tensor product of Bell states.

Bell-diagonal states are 2-qubit states that are diagonal in the Bell basis. Since those states lie in $\mathbb{C}^{2} \otimes \mathbb{C}^{2}$, the Peres-Horodecki criterion is a sufficient condition ...
4
votes
3answers
563 views

Assumptions in Bell's Theorem

It is often Stated that Bell's Theorem is equivalent to the statement: No theory of Local Hidden Variables can reproduce all of the predictions of quantum mechanics. I see nowhere in Bell's Theorem ...
1
vote
1answer
70 views

Photon source for Bell test

Wiki tells us that In practice most actual experiments have used light, assumed to be emitted in the form of particle-like photons (produced by atomic cascade or spontaneous parametric down ...
10
votes
2answers
485 views

Interpretation of “superqubits”

Two very intriguing papers recently appeared on the arXiv, claiming that one can use "superqubits" -- a supersymmetric generalization of qubits -- to violate the Bell inequality by more than standard ...
3
votes
2answers
641 views

Can cellular automata be reconcilied with quantum mechanics?

CAs are deterministic representations of the universe, which, according to the Bell's inequality are not entirely accurate. Cells interact "locally" (only with the closest neighbours), while quantum ...
3
votes
1answer
415 views

Why does quantum mechanics invalidate one of locality and realism?

I am approaching this from an intuitive perspective and I don't speak the language. However, I have been doing a lot of reading about Bell's Theorum and how invalidates either locality or ...
1
vote
1answer
185 views

On Bell's Inequality (Classical Intuition) and Quantum Mechanical Counter Intuition

This posting is directly related to the issue in The System and the Measuring Gadget. The QM expectation is given by: $$\langle\sigma_{1}.\vec{a}{\;}\sigma_{2}.\vec b\rangle=-\vec a.\vec b$$ In the ...
0
votes
0answers
82 views

Would Einstein have accepted the presumptions that lead to the Bell inequality?

To check the correlation between Hidden Variable Theory and Quantum Mechanics, Bell calculated the expectation value $<\sigma_{e}(\vec a,\vec V) \sigma_{p}(\vec b,\vec V)> = \int d^n V ...
6
votes
2answers
355 views

Show quantum entanglement to a classical thinker

Can someone describe a simple experiment to convince a person thinking about physics classically (called Claus) that quantum mechanics has something weird, entangled? I mean an experiment that he ...
2
votes
1answer
152 views

What exactly does $S$ represent in the CHSH inequality $-2\leq S\leq 2$?

What exactly does $S$ represent in the CHSH inequality $$-2~~\leq ~S~\leq ~2?$$ Sorry I've been reading for a couple days and I can't figure out what exactly $S$ is and the math is a bit over my ...
1
vote
0answers
55 views

What characterizations are available for two-photon Bell state light sources?

It is often technologically important to know how photon statistics change over time when a light source is turned on. A light source that comes to full intensity/visibility in a nanosecond after it ...
12
votes
6answers
2k views

Disproof of Bell’s Theorem

The half-page arxiv doc by Joy Christian of Oxford Uni, UK has the Title and Abstract: Disproof of Bell’s Theorem We illustrate an explicit counterexample to Bell’s theorem by constructing a ...
11
votes
3answers
682 views

Bell's theorem and why nonlocality is problematic

I generally hear it assumed that Bell's inequality implies violation of counterfactual definiteness, because locality is considered sacrosanct. I understand of course that measurable violations of ...
5
votes
2answers
486 views

How can we be sure that nature isn't “faking” quantum statistics?

In a recent publication, Experimentally Faking the Violation of Bell’s Inequalities (Gerhardt 2011) (arXiv version), the statistics of quantum mechanics is faked using classical light sources. But if ...
2
votes
0answers
133 views

Do Bell inequality violations appear instantly when the source is turned on, or do they increase over time?

This experimental Question is a result of reading a particular article on Bell violations. I addressed the e-mail below to the corresponding authors —because who knows, they might reply— but it is not ...
14
votes
0answers
253 views

Bell polytopes with nontrivial symmetries

Take $N$ parties, each of which receives an input $s_i \in {1, \dots, m_i}$ and produces an output $r_i \in {1, \dots, v_i}$, possibly in a nondeterministic manner. We are interested in joint ...