Free Will

Even though I am a scientist, very few (if any) of my posts have been discussing anything particularly scientific. They’ve mainly been about things like higher education, scientific policy and politics. Something in a recent New Scientist , however, caught my eye and I thought I would write a short post about it.

The article was about free will and I started reading it at coffee before anyone else had arrived. I didn’t finish as others arrived before I could do so, but from what I read the article was discussing how we might respond if we were lead to believe that we didn’t have free will. Would we begin to do things that we might not have done otherwise because we believed we had no control (or responsibility) for our actions.

I haven’t given the concept of free will much thought, but have always assumed that it is related to Quantum Mechanics . It is Pierre-Simon Laplace who is often regarded as having said something along the lines of “if you give me the positions and momenta of all the particles in the universe I can predict the future”. I know he didn’t say exactly this, but it was essentially this. The reason this is “wrong” is that quantum mechanics, through Heisenberg’s Uncertainty Principle, tells us that it is not possible to determine, exactly, the position and momentum of a particle.

I’ve got to admit that I haven’t really done any quantum mechanics (or thought very hard about it) since I was an undergraduate many years ago, but my memory of what I was told was that there are two interpretations of quantum mechanics. One is that particles do have a well-defined position and momentum, we just can’t measure them both exactly. The other (which I believe is largely accepted) is that particles do not actually have a well-defined position and momentum. They exist in a superposition of states (wave-particle duality), and when some kind of interaction occurs the momentum and position of a particle involved in the interaction is not pre-determined. There will be a range of possible positions and momenta, essentially represented by a probability distribution. There will be a most-likely position and momentum, but a finite chance that the particle will take on a different position and momentum.

I had always assumed that this property of quantum mechanics is what essentially gave us free will. If all particles in the universe initially had a precisely defined position and momentum then it seems that their evolution must be predetermined. How can we choose how to move if all the particles from which we are formed have a predetermined evolution. Maybe I’m wrong about this, but it seems that if the initial conditions of the universe are precisely defined then the evolution is predetermined. It may be chaotic and we may be unable to model it (i.e., it may not be possible to measure the positions and momenta with sufficient accuracy) but it would be predetermined nonetheless.

Quite how quantum mechanics gives us free will, I don’t know. Maybe there is some kind of uncertainty in exactly how neurons fire. Furthermore, how do we actually control this and does it have implications for quantum computing (I’m sure someone must have considered this already). Additionally if we can show definitively that we have free will, does that prove that quantum must be, at least in principle, true. Alternatively, as I’ve already said, maybe I’ve missed something obvious and this is all bollocks.

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