54 votes

How do we know that entanglement allows measurement to instantly change the other particle's state?

The assumption that a measurable property exists whether or not we measure it is inconsistent with the experimental facts. Here's a relatively simple example. Suppose we have four observables, $A,B,C,...
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13 votes
Accepted

Does the following experiment disprove the Copenhagen interpretation?

Garret's presentation of what he calls the "Einstein-Podolsky-Rosen-Garret" paradox, in the 25:00 - 29:00 range of the video you link to, is not sound. Garret proposes a source of entangled particles ...
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11 votes

Why is the quantum Venn diagram paradox considered a paradox?

I think the most intuitive answer for why this is a "paradox" is because it behaves differently than other types of filters such as color filters. In the case of non-polarized filters, the behaviour ...
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10 votes
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Was quantum mechanics made to fit the Bell violations or they just happen to fit them?

It's not completely clear what you're asking, but I can make one thing clear: quantum mechanics was not developed with the specific aim of correctly describing the precise amounts to which CHSH ...
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9 votes

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

Here are some facts: As others have said, the evolution of a quantum state, including entanglement, can be simulated arbitrarily well classically with sufficient resources. Actually, modelling the ...
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  • 7,052
9 votes
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Does Bell's theorem imply a causal connection between the measurement outcomes?

It kind of does, but in a useless way. The question is essentially equivalent to the following simplified version of it: suppose a probability distribution $p(a,b)$ cannot be factorized as $p(a)p(b)$....
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9 votes

In Bell's experiment, can "knowing the future" be that "hidden variable"?

Bell's inequalities hold more generally. You can verify the existence of nonclassical correlations in a variety of platforms, including those that have nothing to do with photons or light in general. ...
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8 votes

Can someone clarify whether the recent experiment closing all remaining loopholes to Bell's Theorem really shut the door on local realism for good?

Let's assume for the sake of argument that the experimentalists here did a good job, didn't make any obvious mistakes, and will be confirmed by future experiments of this type**. My understanding is ...
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  • 7,052
8 votes

Is there any version of Bell's inequality when $d >2$?

There are Bell inequalities for basically all scenarios you can think of. To be a bit more precise, I'll refer to a "Bell inequality" as a mathematical inequality describing the correlations of ...
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  • 15k
8 votes
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Where is locality used in CHSH/Bell's inequality?

For better clarity I will here be using the notation $A_0$ and $A_1$, instead of $A$ and $A'$, to denote the outcomes for different measurement setups, and same with $B$. The expectation values are ...
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  • 12.5k
8 votes

Is it possible to actually run Sidney Coleman's "Diehard" experiment?

It has been done: D. Bouwmeester, J.-W. Pan, M. Daniell, H. Weinfurter and A. Zeilinger, Observation of three-photon Greenberger–Horne–Zeilinger entanglement, Phys. Rev. Lett. 82 (7), 1345–1349 (1999)....
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8 votes
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Implications of MIP*=RE for physics?

At first sight the consequences for physics would be earth-shattering: they have showed that there exists a Bell inequality for which the commuting Tsirelson bound is strictly larger than the tensor-...
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8 votes
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Why is the assumption of free will important to physics

Free will is a concept that probably cannot even be defined within the scope of physics. The somewhat related concept that is usually assumed in physics is the absence of superdeterminism. WHAT IS ...
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  • 1,139
8 votes
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Typo in Bell's original paper on the EPR paradox?

Yes, this is a typo on the left-hand side of the second equation; it is correct that $$B(\vec{b},\vec{\lambda})=-\mathrm{sign}\,\vec{b}\cdot\vec{\lambda}.$$ To see how he concludes (10), let's rewrite ...
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7 votes

Couder-Fort Oil Bath Experiments and Quantum Entanglement Phenomena

I think that 't Hooft's ideas about superdeterminism and Bell's theorem are relevant to this topic. If the universe is superdeterministic so that all experiments are determined by initial conditions, ...
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7 votes

What are the Implications of Bell's Theorem?

The conclusion that the violation of Bell's inequalities imply faster than light communication can only be reached in counterfactual reasoning. In our quantum universe counterfactuals ("would X have ...
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7 votes

Why is the quantum Venn diagram paradox considered a paradox?

Not a paradox but it is considered surprising to many as a more natural Venn diagram is expected as explained there, a better explanation is on this part of the follow up video, which as my ...
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6 votes
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Why would classical correlation in Bell's experiment be a linear function of angle?

I think you misunderstood the significance of could for a classical theory. The text below the picture you took from Wikipedia says: "Many other possibilities exist for the classical correlation ...
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  • 109k
6 votes

Why is the quantum Venn diagram paradox considered a paradox?

He rotated the 2nd filter by 45 degrees, allowing photons with polarization of 0 - 50 degrees to come through. This is where your misunderstanding lies. The first filter takes away all the photons' ...
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  • 5,995
6 votes
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Why is the quantum Venn diagram paradox considered a paradox?

To clear your mind I want to tell you in detail how the filters influence the light. A polarizing filter (for some range of light) let 50% of the incoming light through the filter. Behind the filter ...
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6 votes

Is Bells inequality always violated?

There is no "Bell's inequality" (there is one in the original paper, but when people talk about Bell's inequality, that is rarely the one they mean), there are many such inequalities. The basic ...
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  • 15k
6 votes
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How exactly does the proof of Bell's theorem fail if you remove the locality assumption?

In my derivation, I make my error at equation $(2)$, attempting to extend the logic employed by Bell in arriving at equation $(1)$. Bell's local derivation uses the assumption that the system being ...
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  • 412
6 votes

What is the reason for the reported opposite-of-QM handedness of photons in a Bell test with circularly polarized photons?

This is too long for a comment and doesn’t provide a direct answer to your question but consider: Scientific Research Publishing is very probably a predatory publisher. The Wiki article highlights ...
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5 votes

A simple proof of Bell's result

First a quick check: Comparing both experiments, we see that in experiment B we have managed to alter the probability distribution for the values of the x component of the first spin This would ...
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  • 768
5 votes

Marginal and joint probability in quantum mechanics

This is very well explained in "Breuer, Petruccione: Theory of Open Quantum Systems" (section 2.1.4) and I don't really know how it could be explained any better. I will just give a quick overview of ...
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  • 6,336
5 votes

How exactly does the proof of Bell's theorem fail if you remove the locality assumption?

Despite this, both ∫ρ(A(a,c,λ)A(c,a,λ)A(a,b,λ)A(b,a,λ))dλ and P(b,c) are restricted to the range −1≤x≤1, so both inequalities should lead to the same experimental conclusions regarding local realism. ...
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5 votes

How is superdeterminism a loophole to Bell's theorem?

You never get to observe the probability distribution directly. You only make individual measurements and build up statistics by combining these measurements. If we assume that the measurements you ...
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  • 35.5k
5 votes
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What's wrong with this extremely simple hidden variables approach?

In your scheme, the measurement results will be equal if the plane normal to $v$ is between the measurement vectors, and unequal otherwise, so the chance that they'll be equal is linearly proportional ...
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  • 18.1k
4 votes

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

You have to read the experiments of A. Aspect with dynamically changing configuration. Please search in the arXiv quant-ph (http://arxiv.org/list/quant-ph/0402) and you will find a long article titled ...
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  • 6,574
4 votes

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

The difference between statistical physics and quantum mechanics is that, in statistical physics, it is always reasonable to either measure a quantity, or demonstrate that the effect of that quantity ...
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