# Tag Info

13

Oh crud, this! I read this paper a month ago. What Joy Christian does is to write out the Bell inequalities, and then effectively identifies quantum states with the variables in the terms of the inequality. This is silly, for the whole point is to erect the inequalities and then demonstrate how quantum states violate them. Joy identifies the quantum ...

13

While NKS came out with much hype, and with a lot of skepticism from scientists, the scientific ideas there are not completely trivial. I just think they are not foundational for the science of physics (at least not as we know it so far), rather they are foundational for the science of biology. The main discovery made by Wolfram (although with an important ...

10

Wolfram's early work on cellular automata (CAs) has been useful in some didactical ways. The 1D CAs defined by Wolfram can be seen as minimalistic models For systems with many degrees of freedom and a thermodynamic limit. Insofar these CAs are based on a mixing discrete local dynamics, deterministic chaos results. Apart from these didactical achievements, ...

10

Bell's theorems indeed rule out simple theories where hidden variables obey local equations. However, no matter how you reason, it's always at some point where you need another assumption. In its simplest form, it is the assumption that two observers, Bob an Alice, have the "free will" to choose along which axis they will measure the spin of a particle ...

6

My reading of Joy's paper —just as it is, without having carefully read the arXiv paper I cited, nor all of Joy's responses to critics that I also mentioned— is, so far: the left and right hand sides of eq(1) and eq(2), without the central interpolations, state that $A(\mathbf{a},\lambda)=\lambda$ and $B(\mathbf{b},\lambda)=-\lambda$, where ...

6

Helder, A lot of comments surround this question and we are awaiting some further responses from the Author of the papers. However this is my understanding of the conclusion of these papers: Every theory - even classical physics - violates the Bell Inequalities So in a sense there is no dispute with the Bell calculation as a demonstrable result of Quantum ...

6

Shortly after NKS came out, I wrote a review in which I tried to explain why the answer to your excellent question is yes. A deterministic model like Wolfram's can't possibly reproduce the Bell inequality violations, for fundamental reasons, without violating Wolfram's own rule of "causal invariance" (which basically means that the evolution of a CA ...

6

I completely agree with Scott that this particular "Grassmannization" isn't equivalent to what supersymmetry is doing in physics. Supersymmetry is a constraint that picks a subset of theories – ordinary theories with ordinary bosonic and fermionic fields that are just arranged (and whose interactions are arranged) so that there is an extra Grassmann-odd ...

5

What you are looking for is an experiment violating a Bell inequality, like the CHSH inequality. From the redaction of your question, I infer that you've already looked at it but weren't convinced (Tell me if I'm wrong.) Maybe the Memin-GHZ game will convince you. Motivation It is a game where 3 parties (A,B,C) play together against a referee (R). The ...

5

Most of these automata models are deterministic in the same sense as pseudorandom number generators are. For example in the lattice gas models the deterministic rules end up generating noise and large scale fluctuations in accord to the Navier-Stokes equations (including turbulence, although this is computationally impractical because of the large lattice ...

5

This is a truly excellent question in my opinion. It is still being worked on. Here are some professional references that will somewhat clarify the issue, or perhaps even confuse you further: http://arxiv.org/abs/1102.4467 http://arxiv.org/abs/1007.5518 http://arxiv.org/abs/1006.3680 Michael J.W. Hall http://arxiv.org/abs/0808.2178 Travis Norsen ...

4

The issue is locality of what? Which quantities are assumed to be local? If you say the reults of all experiments, hypothetical as well as actual, and say that these must be assignable definite values, then this is in conflict with quantum mechanics. But this is the assumption that is called "hidden variables", the reason is that this is the assumption ...

4

The main question is how do you map the CA to reality? You need to say how you describe an experimental situation in terms of the CA variables. If the map is such that an atom is described by a local clump of automata variables, and a far-away atom is described by another local clump of automata variables far away, it is flat out impossible to reproduce ...

4

In mathematics a super lie algebra is defined as a graded algebra with commutators and anti-commutators satisfying a generalised Jacobi identity. No Grassman variables are needed in the defintion. The osp used for super qubits is a basic example of such an algrebra. This particular supersymmetry algebra cannot be used for SUSY theories in physics because ...

4

In the original EPR gedanken experiment, they assumed two particles that have perfect correlations in position, i.e., they are described by a delta function. That does not pose a problem for a thought experiment but cannot be performed in a lab because such a state cannot be normalized and is therefore unphysical. However, in quantum optics, many ...

3

This is a very specific question. Bell's theorem rules nothing out or in. Bell made the assumption that hidden variables existed, and using simple statistical arguments he derived a set of inequalities. If hidden variables existed they should make a measurable contribution to the correlatiions of spins. Therefore, if the measured correlations satisfied ...

3

What I take to be elementary significant papers on this question pre-date arXiv, so they are unfortunately usually available only behind paywalls. I've always found the simplicity of Willem de Muynck's argument in Physics Letters A 114, 65 (1986), "THE BELL INEQUALITIES AND THEIR IRRELEVANCE TO THE PROBLEM OF LOCALITY IN QUANTUM MECHANICS", somewhat ...

3

Jherico, I see that you are keen in finding answers to your questions, or putting your views across for a debate, and this is really good. This is what science is all about. I think your questions deserve attention and proper debate. Here is an effort from my side to help dilute some of the misunderstanding through the comments section of this forum. ...

2

One change that in some ways is not a change is to embrace "superdeterminism", to take the cellular automaton to determine the free will of the experimenter. In fact, insofar as random number generators determine the choices of measurement direction in most experiments, not the experimenter, it's only necessary to take the cellular automaton to determine the ...

2

I'm not sure it makes sense to ask if Nature is "imitating" Quantum Mechanics. Quantum mechanics is a mathematical model that gives predictions that are in excellent, well so far perfect, agreement with what we actually see. I guess the question is whether QM is just a good approximation to the real world or whether it's an exact description of the real ...

2

Mr. Crowell has yet again demonstrated his total lack of understanding of Bell’s theorem, as well as my argument against it. To begin with, Bell’s theorem has nothing to do with quantum mechanics per se, or classical set theory for that matter. It is a theorem about any possible future theory of physics---without prejudice or preconception displayed by Mr. ...

2

Luboš as always gives a good account. There are many alternate accounts, however, some of which make some sense. Your question is asked in a way that suggests to me a specific type of answer. Einstein locality of the dynamics is very well supported by experiment. If by locality you mean Einstein locality, then there are no "measurable violations of ...

2

Consider two electrons A and B which have perfectly anticorrelated spins, which means if A's spin is measured in any direction and B's spin is also measured in the same direction, the answer is always opposite. In this answer, in everything that follows, I will replace "anticorrelated" with "correlated", so I will pretend that in whatever direction, A and B ...

2

This complicated formal argument is why Bell's original paper spawned countless attempts to circumvent it, and this is why to convince yourself that it can't be circumvented, you should use a case where intuition is firm. A clear argument was presented by Mermin (although Bell notes this too to in his paper some extent, when he states in a one-sentence aside ...

2

The easiest example is the small-angle limit of the classical Bell inequality, which is probably the case where Bell noticed the violation first, since he mentions it explicitly as a particularly intuitive limit in his paper. The situation is this: I have a machine that sends out two particles to two far away detectors. I can measure a yes/no quantity in 1 ...

2

The process used in this kind of source is the spontaneous parametric down conversion (SPDC, see, e.g. Wikipedia for details). It is a nonlinear optical process in which from a photon with angular frequency $\omega_0$ you get two photons with frequencies $\omega_1$, $\omega_2 = \omega_0-\omega_1$. These photons are then phase matched and have correlated ...

2

The $S$ in this inequality is defined as $$S = E(a b) − E(a b') + E(a' b) + E(a' b')$$ where $E(M)$ is the "expectation value of $M$" which means the average value calculated from many repetitions of the same experiment (empirically) or from the probability distributions (theoretically). All the expectation values are taken from the products of two ...

2

The main loopholes were the detection (efficiency) loophole and the locality (or communication) loophole (http://en.wikipedia.org/wiki/Loopholes_in_Bell_test_experiments ). I don't know why or if this time it's going to be different.

2

Bell's theorem basically states that some predictions of quantum mechanics cannot be obtained from a local hidden variable model of the theory. Some people (like Nielsen and Chuang) refer to this as the fact that there cannot exist a local realist theory that has the same predictions as quantum mechanics. Roughly speaking, a local theory is one in which ...

Only top voted, non community-wiki answers of a minimum length are eligible