Saturday, September 7, 2013

Is the wavefunction ontological or epistemological? 

A quantum Randi challenge for Bell's theorem 

 Who is James Randi ( He is a former magician who started debunking charlatans and who offers $1M for anyone able to replicate supernatural activities under test conditions. His You Tube clips are most funny. See for example a classic one:

Now physics is by its very nature against supernatural, but and in particular the quantum mechanics area with its counter-intuitive phenomena attracts lots of attention from general public and people espousing their own theories. These days perpetual motion machines are out of favor, and there is surprising interest in "proving Bell theorem wrong". Those "proofs" are in the same category with bending spoons with your mind, unicorns, and Santa Claus. To recap, Bell theorem proves that there is no local realism and there are no causal explanations possible for quantum correlations. 

Some time ago Sascha Vongehr introduced the idea of a "Quantum Randi Challenge" asking the wannabe disprovers to demonstrate their theories on a computer program. Since I have extensive experience in both worlds of physics and computer programming, I tried to simplify the computer program part and this work resulted in the script presented in the prior post. And now I will explain how it can be changed by anyone to their heart's content.

The Bell theorem pedagogical script can be downloaded from: as Bell1.html.txt. Save it locally and remove the .txt ending in the name. The script is written in Java Script language. Here are some key points about the syntax:

For illustration please refer to this part of the code:

//Dot is the scalar product of 2 3D vectors
function Dot(a, b)
 return a[0]*b[0] + a[1]*b[1] + a[2]*b[2];
  • Comments begin with double slash //
  • All coding lines end with a semicolon ;
  • Code is indented for readability but additional white spaces have no effect
  • Array index are represented by square brackets []
  • Array indexes start at zero a[0]
  • Curly brackets are scope qualifiers { }: all variables declared inside them are not visible outside
  • The language is based on C/C++/Java basic syntax
Now the part that the user is allowed and encouraged to change in order to test different ideas is the following:

function GenerateAliceOutputFromSharedRandomness(direction, sharedRandomness3DVector) {
    //replace this with your own function returning +1 or -1
    if (Dot(direction, sharedRandomness3DVector) > 0)
        return +1;
        return -1;

function GenerateBobOutputFromSharedRandomness(direction, sharedRandomness3DVector) {
    //replace this with your own function returning +1 or -1
    if (Dot(direction, sharedRandomness3DVector) < 0)
        return +1;
        return -1;

I mentioned previously that any local realistic model should respect 3 requirements:
  1. Outputs to be +1 or -1 and the correlation should be computed using the actual experimental values
  2. Outcome independence: Alice outcome should be independent from Bob's outcome
  3. Parameter independence: Alice's measurement direction should be independent from Bob's measurement direction
By code construction parameter and outcome independence are automatically fulfilled. Also Alice and Bob are allowed to share a random sharedRandomness3DVector variable which corresponds to a hidden variable. This hidden variable can be generated by the script when pressing this button:

or the user can manually erase the data and enter it by hand or according to their own "hidden variable theory".
Once that is done, all that remains is to replace the simple model I came up with:

    if (Dot(direction, sharedRandomness3DVector) > 0)
        return +1;
        return -1;

with your own method. Save the file locally and try to reproduce the minus cosine curve in the limit of large numbers. If you can do it without changing the rest of the script, the Nobel prize for you is most likely just a formality at that point (and I'll eat my hat).


  1. It looks like the Quantum Randi Challenge is about to be published in the Annals of Physics:
    with preprint here:
    and a second preprint by Richard Gill which will appear in Statistical Science here:
    and a new blog on the Quantum Randi Chalenge here:

    Perhaps they'll find your online version useful.

  2. That is good news. My sole contribution is pedagogical into simplifying the coding side and making it available to anyone with a web browser, a text editor and rudimentary knowledge of Java script.

  3. Antirealists are promoting the QRC, knowing that it is impossible. As more and more people fail it, they think they are bolstering their cause. They're not. Every time someone fails the QRC, they are demonstrating that it really is impossible, that it cannot be made possible by wishing or believing. That's what realism is. It's the same realism by which the Bell violation was demonstrated in physics. Everyone who tested the Bell inequality found it violated, regardless of what they wished or believed. So the Bell inequality really doesn't apply.

    Realism is not a god of the gaps, as Sascha Vongehr claims. It is a first principle, the most foundational principle of science itself. Without realism, there can only be superstition.

    Sascha makes it clear why he used this phrase when he says that "realism is worse than god" because realism can mean anything. He's got it backwards. Whenever fundamentalists run a campaign to show that God has performed a miracle that is demonstrably false, God can always be something that didn't do what they claimed; but realism can never be something that approves of the campaign.

    Furthermore, by claiming localism should be held onto because it's well-defined and realism isn't, Sascha rejects another first principle of science -- that the reason for making a claim well-defined is to allow it to be falsified. Since localism can so easily be held falsified by the Bell experiments, it has no standing in science anymore.

  4. Collin, you say: "Realism is not a god of the gaps, as Sascha Vongehr claims." I know Sascha and I never heard him stating this. When did he claim this?

    "It is a first principle, the most foundational principle of science itself. Without realism, there can only be superstition."

    Both statements are false. Let's discuss them in turn:
    "It is a first principle, the most foundational principle of science itself." If this is true, what are its consequences? I think realism is confused here with something else which may very well be true. In the QRC context realism means "counterfactual definitness (CFD)"

    "CFD is false" is the following statement: the value of observed quantities in physics (like position, momentum, spin orientation, etc) do not exist until measurement. Sure, QM is probabilistic, but is it because we are clumsy macroscopic beasts, trampling like a bull in a quantum china shop, or really the electron does not have a definite spin direction before measurement. The first position is realism, or CFD and is associated with hidden variable explanations of QM. There are hidden variable models for a single particle able to recover all QM predictions, but John Bell showed that for spatial separated particles (hence realism + locality) hidden variable explanations of QM predictions and experimental results are mathematically impossible. This is the celebrated Bell theorem and QRC is a challenge for all people who do not believe Bell's theorem. QRC says: here is your chance to fame: it is OK not to trust Bell's theorem and its mathematical proof, but then construct a counterexample to Bell's theorem and win a Nobel prize. it cannot be done. It is a pedagogical tool which helps people understand Bell's theorem.

    "Without realism, there can only be superstition." Again, you may be talking about something else which is different than CFD. CFD is demonstrably false and this does not make physicists superstitious. There is only one unpalatable loophole in Bell's theorem regarding CDF. Bell proved CFD+locality to be false, and maybe CFD is true and locality is false. There is such a model constructed, and is called the Bohmian mechanics. However it suffers from 2 major problems:
    1. in Bohmian QM model you get changes faster than the speed of light
    2. Bohmian QM is contextual. This means that in experiment A I measure energy and momentum, and in experiment B I measure energy and position, because position and momenta measurements are incompatible, the energy variable in both experiments are different things. Quite schizophrenic (or contextual as the politically correct term is).

    There is no gap in QM, no god of the gaps, and no superstition either. But nature and QM (which is the best mathematical model of nature we have) violate CFD-a.k.a realism. Any realistic model of nature should obey Bell's inequalities. Bell inequalities are a statement about all realistic models, not about QM. Bell inequalities state:

    (A and not B) + (B and not C) >= (A and not C)

    why? because
    (A and not B) = (A and not B and C) + (A and not B and not C)
    (B and not C) = (B and not C and A) + (B and not C and not A)
    (A and not C) = (A and not C and B) + (A and not C and not B)

    and the last two terms cancel one term from the 2 lines above.

    For example take any 3 characteristics in a group of people:
    A=age > 20 years old
    B=color of the eyes is blue
    C=height > 6 ft

    What you get is a Bell inequality. But nature (and QM) violates this when talking about spin measurement for example. Thus is why QM is deeply unsatisfying to many people. Welcome to the weird quantum world. This is nature really is. Accept the experimental evidence. Your macroscopic intuition built by hundreds of millions of years of evolution is your enemy in the quantum world. The macroscopic world around you is an emergent phenomena just like liquid water is an emergent phenomena of discrete water molecules.