Tuesday, April 16, 2013

Electrons have free will

The free will theorem of John H. Conway and Simon B. Kochen says under basic quantum postulates, electrons have free will if humans do. Here is a new interview on it:
Schleicher: Could you make a simple statement about what exactly, or intuitively, the Free Will Theorem says?

Conway: Yes. [Throws a piece of paper.] I just decided to throw that piece of paper on the floor. I don’t believe that that was determined at the start of the big bang, 14 billion years ago. I think it’s ludicrous to imagine that the entire development of the universe, including, say, this interview, was predetermined. For the Free Will Theorem, I assume that some of my actions are not given by predetermined functions of the past history of the universe. A rather big assumption to make, but most of us clearly make it. Now, what Simon and I proved is, if that is indeed true, then the same is true for elementary particles: some of their actions are not predetermined by the entire past history of the universe. That is a rather remarkable thing.

Newton’s theory was deterministic. In the 1920s, Einstein had difficulties believing that quantum mechanics was not deterministic. That was regarded as a defect of quantum mechanics. Certainly when I tried to learn quantum mechanics and didn’t succeed, I thought it was a defect. It’s not a defect. If the theory could predict what one of those particles could do, then that theory would be wrong, because, according to the Free Will Theorem — supposing we do have free will — a particle doesn’t make up its mind what it’s going to do until it does it or until shortly before it does it.

Let me describe the theorem this way. Suppose there is only a very tiny amount of free will in humans: you can press either button A or button B in a manner that is not predetermined. That is a very tiny part of what we normally consider free will for humans. And if we have that tiny amount of free will, so do the elementary particles, in a sense that a particle in response to some experiment can choose which path, C or D, that it follows. It has free action. It chooses C or D in a manner that is not a predetermined function of all the information in the past history of the universe. Schleicher: You believe that humans have free will. Conway: I do. Strict determinism tells us that all of our actions are predetermined by the past history of the universe. I don’t know, maybe it is. I can’t disprove it. I can prove that I can’t disprove it. I can prove that you [points to Schleicher] can’t disprove it either. But I believe anyway that humans have free will.

Schleicher: That is your belief.

Conway: And it is very strong. If you or somebody else doesn’t believe this, I am not going to argue with you, because I know that I can’t disprove the determinist’s position. After giving lectures on this subject in various places, sometimes I have asked whether there were any determinists in the audience. Usually in an audience of a hundred, twenty people put their hands up. They are usually among the most intelligent members of the audience, because it takes some intelligence to disbelieve something that everybody else feels is obvious or to believe something that everybody else feels is ludicrous. Several times people have come up to me and told me they were determinists and expected me to argue the matter. But since I’ve proved that nobody can disprove determinism, what is the point in trying to disprove determinism? I have no argument with determinists or, I should have said, I have no arguments with determinists.

Schleicher: The usual interpretation of quantum mechanics is that the behavior of the elementary particles is simply random.

Conway: You know, randomness doesn’t help. If the action of each particle were a predetermined function of its past plus a random string of bits, then we might as well suppose that this string of bits was produced just before the universe was created, and this is excluded just as well as totally deterministic behavior.
I would phrase it differently, because "free will" is one of those terms that drives philosophers nuts. But his theorem is correct, and restates longstanding understandings of quantum mechanics. Einstein's ideas about determinism are contrary to quantum mechanics, and so are various naive ideas about randomness. Saying that nature is deterministic or random are both very misleading, at best.


  1. A theorem is a statement of math, not physics. It relies on an explicit model, and it can only be as correct as the model is at describing something. In this case, the model of a particle's spin that the authors of the original essay used does not, as they claim, come from quantum mechanics. It's a strawman definition that they probably just made up.

    1. The 3 assumptions are explained on the Wikipedia page. If those are contrary to quantum mechanics, then please edit the page with a reference to the paper that backs up what you say. The theorem is broadly accepted among physicists.