Saturday, April 24, 2010

Quantum Mechanics Revisited

Looking back over my free will posts, I see that sometimes I seem to be saying that quantum mechanics is important for free will, and sometimes I seem to be saying the opposite. Let me see if I can clear things up.

I have addressed several different issues regarding the free will debate, and quantum mechanics relates to each issue differently.

Determinism and the Consequence Argument: To the extent to which the Consequence Argument depends on the premise of deterministic laws of nature, quantum mechanics is certainly relevant. Since quantum mechanics is an indeterministic theory, if quantum mechanics is a true description of the world, then the Consequence Argument fails. However, we have seen that the fear behind the Consequence Argument is not really the fear of determinism, but of lack of control: If the electrons are in control, then I am not in control. The problem then is not deterministic laws of nature, but any sort of microscopic laws at all.

Predictability: Suppose someone were to write a computer program that accurately predicts everything I will do and say tomorrow. That would be a huge blow to free will (though perhaps not a fatal one). How can I be anything more than a machine if a mere machine can duplicate my actions? Here, I claim quantum mechanics is relevant. Accurate prediction of a classically chaotic system will run up against the quantum limit in a very short time, forcing us to adopt a quantum description. But a quantum description will never produce perfectly accurate predictions: first, because the computer cannot completely replicate my quantum state (thanks to the no-cloning theorem), and second, because quantum predictions are only probabilistic (even if the exact quantum state were known).

Control: Here it gets a bit tricky. We have seen that for me to be in control of my actions, we need a fair amount of determinism in the world. I have been arguing that quantum mechanics has enough indeterminism to make effective prediction impossible. Does quantum mechanics leave us enough determinism for moral responsibility? I suspect it does, but this point clearly needs more investigation.

For now, let me just say that I think the way to proceed is by distinguishing the lower-level and higher-level laws of nature, as I began to do in the previous post.


  1. You mentioned in a previous post that you've been ignoring the Everett interpretation throughout these posts. In my lay opinion (which you might therefore think isn't worth much), from all I've read, the poorly-named MWI seems by far the most coherent and reasonable interpretation (to the point where I'm not sure how it's possible for anyone to favour another) -- and it seems to have the bonus of resolving many other problems including these seeming apparent paradoxes around free will.

    What is your favoured interpretation of QM and what do you think of the Everett one?

    As far as I see, it makes QM irrelevant for free will since everything is deterministic and therefore we are back to the same discussions of free will we were having centuries ago when we believed in deterministic billiard ball particles.

  2. Everett called his interpretation the "Relative State Interpretation," and I think it's an interesting approach that hasn't been developed as fully as it should. Instead, it has been corrupted into the Many Worlds Interpretation, which I find incoherent, unhelpful, and metaphysically absurd. I hope to do a blog post on it sometime (soon?) where I will explain my views.

    I lean toward a statistical interpretation, in which wavefunctions are not physically existing entities but just mathematical tools for describing the world.

  3. I agree in terms of the MWI (as popularly described) being unhelpful, and this is the first version I was exposed to, but it's probably not entirely misleading.

    Looking forward to the dedicated post on this.