28 October 2013

"Written in the Stars" with Prof Jim Al-Khalili

This was another those confluences of good things in one place which meant that I had to be there.

I think that Jim Al-Khalili is the best science broadcaster currently (TV and radio) because of the amount of hard science that he includes. He gave this talk in his role as President of the British Humanist Association, which I belong to. And the talk mixed very hard science with a touch of philosophy.

The question Jim tried to answer was that of free will and he addressed it from a scientific angle, i.e. if the future predetermined and predictable then we have no free will whatever philosophers may think.

He started with four hypotheses drawn from a simple 2x2 matrix, which is exactly how you should approach problems like this.

One on axis there were the choice of the universe is predetermined or random and on the other that we have free will or we do not.

Newton thought that the future was predictable in a mechanical sort of way and Einstein said it was already there, i.e. other times exist in the same way that other places do.

The scientific consensus seemed to be that the universe was both deterministic and predictable, then Quantum Mechanics came along and through some crazy random stuff in to the mix.

Jim spent most of his time showing us just how weird QM is, which was understandable given that is what he does. He talked us through the slit experiment that shows particles behaving as waves except when we watch them. I had seen this done many times before but this was the clearest explanation of the lot.

As a mathematician (well, I do have a degree in mathematics even if it is rather old now) I love the fact that mathematics explains QM perfectly (e.g. the probability model for where a particle is) but physicians do not know what is actually happening in the real world, e.g. what the particle is doing to behave like a wave.

Having spent a long time taking us through QM weirdness, Jim then said that this weirdness disappears as we scale up and disappeared well before we get to human scale and so can be discounted from the deterministic argument, e.g. it does not matter how an individual electron behaves at a point in time as it has now discernible effect even at the molecular level.

So the universe could be deterministic (i.e. it has to behave the way that it does) but that is not the same as saying that it is predictable (i.e. we can tell what it is going to do).

The main argument here came from an extrapolation of Poincare's three bodies proof which showed that even very small differences in the starting conditions can lead to very different outcomes. This has been popularised as the Butterfly Effect. The point of this is that we can never know enough about the starting conditions to predict how things are going to behave.

The summary of all this is that Jim claimed that the world is deterministic but we can never know enough to predict it, so it is undetermined to us and, for all practicable purpose, we have free will.

The QandA session that followed showed how little most people know about QM and a lot of time was spent revisiting some of the arguments.

It struck me then that we, the human race, have a cognitive issue here (Martin Rees has said much the same) in that our thinking is conditioned by and limited by our brains which have evolved to solve one set of problems. That is why we cannot comprehend the scale of the universe or the behaviour of very small things. For example, in our human-scale world we are used to an object being in one place at two times but we cannot make sense of an object being in one time at two places.

There is also the very real possibility that our brains are incapable of understanding everything about the way that the universe works, much as a dog is incapable of learning French. That we may never know how QM works is a sobering thought.

During the QandA Jim opened a potential gap in his argument from his current work in the new field of Quantum Biology where a quantum change in a single molecule of DNA could lead to a significant change to the observable world.

I think there is a more obvious flaw. It is easy to devise a mechanism that scales the random quantum world up to the observable world and thus stops it from being deterministic - and you only have to devise the mechanism to make the world non deterministic, you do not actually have to build it. One such a machine would be to select a single Uranium atom and take one significant action if it decays in less than the half-life and another if it does not.

Sadly we ran out of time for me to put this him but I was able to grab a very quick word with Jim on his way out. Obviously that quick word was about Leeds United, the team we both support.

I might dispute his conclusion but Jim is a good presenter and he put the question and some of the implications very well, and dealt with the questions likewise, which made it a stimulating and though-provoking evening.

1 comment:

  1. It sounds fascinating subject matter, Matt, although to be honest QM feels beyond my powers of comprehension. I'll probably forward this onto to my daughters boyfriend, Chris, who I think is studying QM as part of his degree. I'm sure he'll be interested in it - he hopes to become a physics teacher.


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