When scientists are unable to accurately predict things like the weather, they sometimes state that the systems they are failing to predict are stochastic. Those championing determinism would counter that they are not strictly stochastic but that the apparent randomness is due to our failure to identify the equations that accurately describe the system. We might think the weather is stochastic, but this apparent randomness may simply be because we are not very good at predicting the weather more than a day or two into the future. When we discover the right equations, we will be able to accurately predict that 4.2 millimetres of rain will fall on the Champs-Élysées between 9 a.m. and 10 a.m. on 7 January 2081 and we would classify the weather as being deterministic.
One consequence of a deterministic universe, where everything is theoretically perfectly predictable, is that all our actions would be predetermined and we would have no free will. The ways that the atoms from which our brains are built interact with one another would be inevitable, and so too would be each of our actions. Free will would be an illusion in a deterministic universe. I would have been destined to write this book 13.77 billion years ago when the universe began, and I never really made the decision to do so. I could never have resisted the urge to write it, even if I had wanted to. You, too, were destined to buy it.
The idea of free will being an illusion will sit badly with most people, and personally I don’t like it. The choices I make feel very real, and I believe we are responsible for our actions. I do not like the idea that our actions might be completely predictable. However, this is just a feeling, and is not scientific. Just because I don’t like a hypothesis does not mean it isn’t true.
Quantum mechanics very accurately describes the behaviour of the very small, and all the evidence says that aspects of the behaviour of particles such as electrons are random. In my opinion, Occam’s razor, the argument that explanations should be as simple as possible yet no simpler, points to a stochastic universe. Once again, such an argument is based on opinion rather than science. These feelings are, of course, important, but they are not scientific. You and I are made from particles, and particles obey the law of physics, so if their behaviour is predictable, then does that mean our behaviour must be deterministic? To disprove the idea of determinism I need to offer an alternative, and the alternative must explain where randomness comes from.
The only true source of randomness so far identified in the universe is described by the theory of quantum mechanics, something I described when discussing the two-slit experiment. Quantum mechanics accurately, yet probabilistically, describes the behaviour of electrons, protons, neutrons and atoms. It is one of the greatest achievements of physics, and explains one of the most peculiar aspects of our universe: that particles are also waves. The theory describes properties of particles as probability distributions. For example, a particle’s position is described with a wave function, which describes where it is more likely to be, and where we’d be unlikely to find it. Although we cannot directly observe the wave function of any particle, because measuring it would force the particle to entangle with our measurement device causing the particle’s wave function to collapse, we can imagine what it would look like if we could. If we were to scale the quantum properties of particles like electrons to the scale of our solar system, the moon (and sun and all the objects in the night sky) would appear as a distant mist, with some parts of the mist being thicker than others. The thicker parts would be where the moon would be most likely to appear if forced to interact with something.
Quantum mechanics is the most successful theory in science. It very accurately describes how fundamental particles behave, yet despite this accuracy, some physicists argue about the interpretation of the theory. Some claim that the apparently unpredictable and random behaviour of particles will eventually prove to be deterministic, and when that happens free will will be banished to the trash can of discredited ideas. One example of a hypothesis that makes the random behaviour of particles predictable is the Many Worlds hypothesis. Put very simply, and skating over many nuances, this states that we experience one outcome when a wave function collapses, but that all possible outcomes occur in parallel realities that we do not experience. It is a clever way of making the stochastic deterministic by saying all possible things that could happen do, but that we only experience one of the outcomes – our reality.
I didn’t mention the Many Worlds hypothesis, or other interpretations of quantum mechanics, earlier in the book when I described the two-slit experiment, because they are currently untestable. There is no evidence for realities beyond our own, and at present there is no way of testing hypotheses that predict them. The Many Worlds hypothesis provides a way to make our universe deterministic and in that respect it is cute. But many creation myths are quite cute too and that doesn’t make them right.
Untestable thought experiments such as the Many Worlds theory play an important role in science. They allow us to think through a range of possible interpretations. What I don’t understand is why there is a desire among some physicists to prove the universe is deterministic. The available data we have suggests the behaviour of fundamental particles is stochastic, and that opens up the possibility of a stochastic universe and of free will. But it creates a new challenge – how does randomness at the level of the tiny particle translate into non-deterministic behaviour of much larger objects such as you and me?
When the wave function of a particle collapses, such as when a single atom collides with the detector screen in the two-slit experiment, the particle becomes entangled with the detector screen – an object whose wavelength is so small it can be ignored and which behaves like those we are familiar with in everyday life. The screen is designed to detect the particle by interacting with it, and the screen and the particle become a single object. The screen and entangled particle are a large object consisting of millions of atoms, and it behaves like all large inanimate objects in predictable ways. Knock it off the bench and it will fall to the floor, or throw a ball at it and the object and the ball will bounce off it. It is such reassuring, familiar behaviours that make the idea of a deterministic universe attractive to some scientists. But not all solid objects behave quite like detector screens, and perhaps life has found a way to exploit the random behaviours of particles to enable free will.
The field of quantum biology is in its infancy, but exciting insights are beginning to emerge. For example, photosynthesis, the process by which algae, some bacteria and all plants create sugars from sunlight, water and carbon dioxide, relies upon quantum mechanics to transform photons of sunlight into energy that can be used to produce sugars. Photosynthesis evolved early in the history of life, perhaps as long as 3.5 billion years ago, suggesting that life discovered how to exploit quantum behaviour early on.
Evidence is also beginning to emerge that quantum mechanics plays a role in the workings of some enzymes, in the way neurotransmitters work in the brain, and recently biophysicists at the University of Surrey in the UK have data and models that point to some genetic mutations being due to quantum randomness. Genetic mutations influence the development of embryos, and are the fuel for evolution and the spread of life, providing some evidence that we owe our existence to stochastic processes, and that we were not inevitable at the birth of the universe. You and I would not occur in my universe rerun experiment if the universe is stochastic and quantum processes influence evolution.