Do we have free will – a physicist’s perspective?


This blog was prompted by an online article I was alerted to by Roger Highfield on Twitter, which discussed how neuroscientists were conducting experiments suggesting that free will is indeed just an illusion. It was rather dismissive of the years (no, make that centuries) of philosophical debate that has seemingly not brought us any closer to an answer. Now, as a physicist I am usually at the front of the hard-nosed scientist queue when it comes to philosophy bashing. But on this issue, I am not so sure.

Are we really part of a clockwork universe?

What follows is a bit of a cheat, because this is an edited version of part of a chapter from my bookParadox: The Nine Greatest Enigmas in Science, in which I discuss something called Laplace’s demon. Anyway, it is a theoretical physicist’s ramblings that may be seen by neuroscientists and psychologists as fluffy philosophy, and philosophers will just think it naïve. But there you go.

Let me begin by carefully distinguishing between three concepts: determinismrandomness andpredictability. Firstly, by ‘determinism’ I mean what philosophers refer to as causal determinism: the idea that events in the past cause events in the future. And it follows, taking the idea to its logical conclusion, that therefore everything happens for a reason that can be traced all the way back to the birth of the Universe itself.

In the seventeenth century Isaac Newton came up with his laws of mechanics using the newly understood mathematics of calculus, which he was instrumental in developing. His equations allowed scientists to predict how objects move and interact with each other, from the firing of canon balls to the motion of the planets. Using mathematical formulas in which values for physical attributes of an object, such as its mass, shape and position, its speed and the forces acting on it, could be plugged into simple equations that could provide information on the state of the object at any future time.

This led to the widely held belief, which lasted for the next two centuries, that if all the laws of nature could be known it would in principle be possible to compute the future action of every object in the Universe. It was a universe in which everything – all movement, all change – was predetermined. There was no free choice, no uncertainty and no chance. It became known as the Newtonian clockwork universe. At first glance, it is not as bleak as Einstein’s block universe, in which everything that has ever happened and will ever happen in the future is laid out frozen in time before us. But in fact, the clockwork universe is no different in the sense that it also gives us a universe in which its state at all future times is indeed predetermined and fixed.

Then this view suddenly changed. In 1886, the King of Sweden offered a prize of two and a half thousand Kroner (a tidy sum and more than most would earn in a year) to whoever could prove the stability of the solar system; that is, whether the planets would continue to orbit around the sun forever or if there was a chance that one or more of them might one day spiral into the sun or escape the pull of its gravity and float away? The French mathematician Henri Poincaré took up the challenge and began by looking at a simpler problem involving just the sun, the earth and the moon – what is referred to as a three-body problem. He discovered that even with just three bodies, the problem was mathematically impossible to solve exactly. What’s more, certain arrangements of the three bodies would be so sensitive to initial conditions that the equations pointed to completely irregular and unpredictable behaviour. He won the King’s prize even though he didn’t come up with an answer to the original question about the stability of the whole solar system.

Poincaré had discovered that even the way a system of just three interacting bodies evolves in time could not be knowable exactly, let alone one involving all bodies in the solar system (at least all the planets and their moons, along with the sun). But the implications of this would have to wait another three-quarters of a century.

When it comes to what all this has to say about the nature of free will, there are still many different philosophical views and the issue is far from resolved. All I can do is give you my opinion as a theoretical physicist. You are free to disagree with me. Or are you?

There are four options available when it comes to the sort of universe we live in:

(i) Determinism is true so all our actions are predictable and we have no free will, just the illusion that we are making free choices;

(ii) Determinism is true but we can still have free will;

(iii) Determinism is false; there is built-in randomness to the Universe allowing us the room to have free will;

(iv) Determinism is false, but we still don’t have free will since events happen randomly that we have no more control over than we would if they were predetermined.

Scientists, philosophers and theologians have debated whether or not we have free will for thousands of years. I’m going to focus here on certain aspects of the nature of free will and its connection with physics. I certainly won’t be straying into the realm of what is called the mind-body problem, the nature of consciousness or the human soul.

Our physical brains, consisting of a network of a hundred billion neurons that are linked together via hundreds of trillions of synaptic connections are, according to everything we know about them so far, nothing more than sophisticated and hugely complicated machines that run the equivalent of computer software, albeit involving a complexity and interconnectedness far beyond anything a modern computer can achieve. All those neurons consist ultimately of atoms that obey the same laws of physics as the rest of the Universe. So if we could, in principle, know the position of each atom in our brains and what it was doing at any given moment and we understood fully the rules that govern how they all interact and fit together, then we should in principle be able to know the state of our brains at any time in the future. That is, with enough information I could predict what you will do or think next – provided of course you are not interacting with the outside world, otherwise I will need to know everything about that too.

Were it not therefore for the weird and probabilistic quantum rules according to which those atoms behave, and in the absence of any non-physical, spiritual or supernatural dimension to our consciousness of which we have no evidence, we would have to admit that we too are part of Newton’s clockwork, deterministic universe and that all our actions are preordained and fixed in advance. In essence, we would have no free will.

So do we have free will or don’t we? The answer, despite what I have said about determinism, is yes I believe we still do. And it is rescued not by quantum mechanics, as some physicists argue, but by chaos theory. For it doesn’t matter that we live in a deterministic universe in which the future is, in principle, fixed. That future is only knowable if we were able to view the whole of space and time from the outside. But for us, and our consciousnesses, imbedded within space-time, that future is never knowable to us. It is that very unpredictability that gives us an open future. The choices we make are, to us, real choices, and because of the butterfly effect, tiny changes brought about by our different decisions can lead to very different outcomes, and hence different futures.

So, thanks to chaos theory our future is never knowable to us. You might prefer to say that the future is preordained and that our free will is just an illusion, but the point is our actions still determine which of the infinite number of possible futures is the one that gets played out.

Consider the situation, not from our own point of view looking out at the deterministic yet unpredictable world around us, but by examining the complexity of our brains and how they work. It is precisely this unavoidable unpredictability about how a complex system such as our brain works, with all the thought processes, memories, interconnected networks with their loops and feedbacks, that gives us our free will.

Whether we call it true freedom or just an illusion in a way does not matter. I can never predict what you might do or say next if you really want to trick me because I cannot in practice ever model every neuronal activity in your brain, anticipate every changing synaptic connection and replicate every one of those trillions of butterflies that constitute your conscious mind in order for me to compute your thoughts. That is what gives you free will. This despite the actions of the brain most probably remaining fully deterministic – unless quantum mechanics has a bigger say in the matter than we currently understand.