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31
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5answers
4k 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 ...
17
votes
0answers
374 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 ...
16
votes
7answers
3k 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 ...
15
votes
5answers
1k 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 ...
12
votes
3answers
991 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 ...
11
votes
1answer
723 views

Why can't I use Bell's Theorem for faster than light communication?

I read this description of Bell's theorem. I understand he's restating it slightly, so there may be incorrect assumptions there, or I may have some. I think Bell's theorem should lead to FTL ...
10
votes
2answers
719 views

Why was quantum mechanics regarded as a non-deterministic theory?

It seems to be a wide impression that quantum mechanics is not deterministic, e.g. the world is quantum-mechanical and not deterministic. I have a basic question about quantum mechanics itself. A ...
9
votes
2answers
542 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 ...
8
votes
3answers
1k 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 ...
7
votes
2answers
431 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 ...
6
votes
6answers
308 views

Can quantum entanglement be simulated on a digital computer to any degree of precision?

First principles modelling of physical phenomena has been very successful in physics. The largest limitation is perhaps the fact that many QM problems are NP hard so we would need really powerful ...
6
votes
1answer
126 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 ...
6
votes
2answers
3k views

Bells Theorem for Dummies, How does it work?

I've been reading up on theoretical physics for a few years now and I feel like I am starting to get an understanding of particle physics, at least as much as you can from Wikipedia pages. One thing ...
6
votes
2answers
252 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 ...
5
votes
3answers
786 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 ...
5
votes
2answers
683 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 ...
5
votes
3answers
257 views

Why would classical correlation in Bell's experiment be a linear function of angle?

Sorry if it's a newbie question, but I have trouble understanding the following part in the Wikipedia's explanation for the Bell's theorem: With the measurements oriented at intermediate angles ...
4
votes
4answers
690 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 ...
4
votes
2answers
243 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 ...
4
votes
2answers
339 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 ...
4
votes
2answers
942 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 ...
4
votes
2answers
143 views

Does Bell's theorem rule out the possiblity that measurements are completely determined by events in the past light cone?

I'm studying Bell's theorem and the CHSH inequality for some time. Now it's clear to me that one cannot reproduce the correlations predicted by quantum mechanics by assuming that particles carry ...
4
votes
1answer
246 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 ...
4
votes
1answer
221 views

Entanglement, Bohr-Einstein Debate, Bell's Inequality

On BBC episode The Secrets of Quantum Physics (Part 1) Jim Al-Khalili explains quantum mechanics for the layman. In the first half, he does a very good job; in the second half, either he thought his ...
4
votes
1answer
497 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 ...
3
votes
1answer
118 views

Was quantum mechanics made to fit the Bell violations or they just happen to fit them?

Entangled bipartite states can violate the CHSH inequality upto $2\sqrt{2}$ with suitable measurements. Is it that in nature we don't witness violation of CHSH more than this and quantum mechanics ...
3
votes
2answers
1k 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
2answers
390 views

Why isn't the best case classical solution to the CHSH game 100%? [closed]

[Edit 2] I would prefer to just forget that I had ever asked this question (because I was so wrong it's embarrassing), but for the sake of people who possibly make the same mistake I did, I'll try to ...
3
votes
1answer
378 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 ...
3
votes
1answer
76 views

How are the PPT criterion and Bell's inequality different?

Bell (1964) writes that if we assume an equivalent classical hidden variable distribution for a two-qubit state then the expectation value of the product of two observables $A$ and $B$ can be written ...
3
votes
1answer
63 views

Bell inequality with triplet state

Is it possible to prove Bell inequality starting from a state formed from triplet states, i.e. $\frac{1}{\sqrt{2}}(|\uparrow>_A|\uparrow>_B+|\downarrow>_A|\downarrow>_B)$? If not, why? ...
3
votes
2answers
132 views

Does Bell's inequalities also rule out non-computable local hidden variable theories?

I have beenn reading different articles on Bell's assumptions and interpretations, including superdeterminsm. I always end up dizzy when I try tho think about this specific question, so any hints ...
3
votes
1answer
513 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 ...
3
votes
1answer
708 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 ...
3
votes
2answers
66 views

Non-locality vs. non-realism: Arbitrary choice?

After reading this question, I feel I understand why quantum mechanics is so confusing (and so often confused by the media): It can be either local (if A causes B, then there must be time for a signal ...
3
votes
0answers
52 views

What makes Bell's original inequality unsuitable for experiments?

Bell derives the inequality $$|E(\vec{a},\vec{b})-E(\vec{a},\vec{c})|\leq 1+E(\vec{b},\vec{c})$$ in his book Speakable and unspeakable in quantum mechanics. In this derivation he uses the assumption ...
3
votes
6answers
392 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, ...
2
votes
1answer
161 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 ...
2
votes
2answers
217 views

Why are results of Bell's experiments considered to “break realism”?

Related to my previous question (Why would classical correlation in Bell's experiment be a linear function of angle?), as a newbie in quantum mechanics, I am also unable to find the reason to why ...
2
votes
1answer
258 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 ...
2
votes
2answers
456 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 ...
2
votes
2answers
71 views

Can the measurement apparatus cause correlations that violate the Bell's inequality?

If you drop a coin it's affected by the air drag, bounces and tumbles on floor before it settles and you can read whether it was heads and tails. If I understood it right, the Bell's theorem says ...
2
votes
1answer
101 views

Are there any experimental tests of non-locality / Bell inequalities that do not rely on spin?

All the experiments I know, which have been performed to test Bell inequalities, are somehow based on measuring the spin degree-of-freedom of some particle (usually photons, sometimes electrons). I ...
2
votes
1answer
76 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 ...
2
votes
2answers
249 views

What are the Implications of Bell's Theorem?

Consider the following game show: two friends Tom and Jerry (X and Y) are selected from an audience to compete for a grand prize, a brand new Ferrari. The game description: The two contestants ...
2
votes
1answer
248 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.
2
votes
0answers
20 views

Does the trial index of typical CHSH experiments constitute a “hidden variable”?

In typical experiments related to the CHSH inequality there are individual detections being made by two separate (analyzer-and-)detector systems, "System $A$: $(D_A^+, D_A^-)$" and "System $B$: ...
2
votes
0answers
73 views

Is there a cheap way I can do a Bell inequality experiment?

My work is almost completely theoretical/computational. But I'd really like to do a Bell inequality experiment just so I can personally see this (the best way to learn something is hands-on, right?) ...
1
vote
2answers
143 views

Is entanglement a classical phenomenon (last attempt)?

This is a reformulation of two previous questions that seem to have been misunderstood, or most likely, I failed to make them clear. I thank all people that answered, even the belligerent ones. Some ...
1
vote
2answers
180 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 ...