It’s not easy, getting a PhD in physics. Not only must you learn a lot, but some of what you learn will shake your sense of self.Philosophers, to quote Bordieu, loathe determinism. It’s true. I will discuss this some other time.
Physics deals with the most fundamental laws of nature, those from which everything else derives. These laws are, to our best current knowledge, differential equations. Given those equations and the configuration of a system at one particular time, you can calculate what happens at all other times.
That is for what the universe without quantum mechanics is concerned. Add quantum mechanics, and you introduce a random element into some events. Importantly, this randomness in quantum mechanics is irreducible. It is not due to lack of information. In quantum mechanics, some things that happen are just not determined, and nothing you or I or anyone can do will determine them.
Taken together, this means that the part of your future which is not already determined is due to random chance. It therefore makes no sense to say that humans have free will.
I think I here spell out only the obvious, and use a notion of free will that most people would agree on. You have free will if your decisions select one of several possible futures. But there is no place for such a selection in the laws of nature that we know, laws that we have confirmed to high accuracy. Instead, whatever is about to happen was already determined at the big bang – up to those random flukes that come from quantum mechanics.
Determinism appears in its modern form with a popularisation of Laplace’s Celestial Mechanics, the first modern book of modern theoretical astronomy. Laplace derived the motions of the planets, it seemed, from Newton’s laws and the inverse-square law of gravitational attraction, and famously did not need God to keep the whole thing running smoothly or from flying off into the rest of space. This was hype: with the techniques Laplace had, it is impossible to solve for the orbits of the Sun, Moon and Earth simultaneously, let alone all the other planets. Today it can be done with computers, and we have a qualitative understanding about the prevalence of unstable orbits as against stable ones, but we don’t have a neat solution to the three-body problem.
This didn’t stop the hype merchants. Given Laplace’s equations, they said, and the initial position and momentum of all the bodies in a system, the future behaviour of those bodies could in principle be calculated, and even if it couldn’t in practice, the fact was that the future behaviour of those bodies was already determined by the present conditions. Hence determinism.
This is kinda okay for planets and vibrating bridges, but once you add in the idea that people are merely particles of change…orbiting around the sun and so equally the subject of determinism, you get materialist determinism, which says it’s to nobody's fault or glory that they do anything, because it was all arranged at the start of the universe. It’s a tough one to dispel.
So what’s the flaw, and why is it hype, not fact? Let’s deal with those Laplacian differential equations first.
The mathematics says that, for a system of differential equations to have an unique solution between two time periods, and hence determine one and only one world between those points, these boundary conditions must be at the start and the end of the time period. If there are only conditions at the start, we get a whole bunch of solutions, any one of which is possible. At the moment of the Big Bang, to speak in metaphors, the Universe might know where it is, but it doesn’t know where it’s going, so it can’t travel along an unique path to get there. If the Universe depended on looking at differential equations to know what it should be doing, it would have too many choices, and wind up in the physics department at Stanford talking about multiverses.
Fortunately the Universe does not depend on differential equations: it uses the laws of nature. Differential equations are not laws of nature. The wave equation, the telegraphy equation, the Schrodinger, Dirac, and other equations are derived from a description of a physical system and the actual laws of nature. These are, roughly and incompletely:
1. The first two of Newton’s three laws (the third is an scheme for model-construction)
2. Noether conservation laws derived for whatever fields we think the universe has in it
3. Lorentz-Firzgerald co-ordinate transformations for local physics
4. Co-ordinate invariance for General Relativity
All of these describe constraints on spatio-temporally local interactions. Laws of nature determine what happens to certain quantities in individual interactions involving those quantities. There are no consequences for the future.
Speaking in metaphors again: after the Big Bang, the universe carried on as it was, and every time an interaction came along, sorted itself out according to the relevant laws of nature. But there never was a Grand Plan or a Final Destination. The Universe just kinda bumbles along. Sufficiently isolated systems with periodic behaviour will repeat themselves, but the journey of a piece of cosmic dust across the universe is an adventure, not a train ride.
This disposes of the everything-was-already-decided-at-the-Big-Bang (or any other later time) claim. Which leaves materialism.
Materialism insists that this is a material world, and hence that free will can only exist if there is within us something which is a) the seat of our identity, b) can cause us to act, c) cannot be acted upon by the material world, but d) can receive and process information. Sometimes called a mind or a soul, but always assumed to be immaterial. In a material world there are no immaterial minds, and hence no free will.
Materialists prefer to denounce free will, decision-making and other mental acts, especially those playing a role in rational action and thought, as illusions, delusions and confusions. Or at least the ones writing pop-science best-sellers do.
If this is only a material world, then what we thought were immaterial mind-acts like remembering, deducing, judging, guessing, and all those other thinking- and feeling- acts, are still done, but by the body and brain. Some philosophers get very snotty about brains, which are after all organic computers, doing anything mental, because someone programmed the computer and so that doesn’t count. They forget they were trained to know where A-sharp is on the top string of a violin, and to calculate zero-th cohomology groups, and that training and learning is the model for ‘training’ AI programs. That means they might be computers, which makes them feel a bit squirmy.
Descartes and those mad white-coated scientists in black-and-white 1960’s Sci-Fi TV programmes regarded the body as a useless hindrance to the mind, which if put into this glass dome would be able to think unthinkable thoughts… okay. You get the idea. The mind-body duality is silly, and entrenched in our culture. As enlightened materialists, we don’t think like that. Brains are part of our bodies, and our bodies are, like the book title said, our selves. The ‘I’ that learns, considers, has goals, and makes decisions, is my brain-body.
However the brain-body is constituted, it must be able to adjust itself to what it receives by way of information. In some cases, that adjustment can be huge (birth of children, adolescence) and in others it can be small but significant (not going near chicken again for a while after that food poisoning), and in others can be almost instinctive (way too cold out there, get the coat and scarf). What the materialist determinist claims is meaningless causation, the brain-body sees as information on which it will or won’t act. My material body deals with facts, sets goals, decides what to do, learns from mistakes and changes its behaviour to better achieve those goals. Explaining how that happens is the real challenge for brain psychologists.
So what is it to decide? It’s a brain process, shaped by our brain’s training and learning, which we would call experience, education and any number of other things. Because I am my brain-body, those processes are what it is for me to decide, not some evil bit of mechanics that then fools my conscious mind it did the thinking.
Is my decision free? There’s a thing about ideas like ‘free’, ‘real’, ‘genuine' and some others. What these kinds of words signify is the lack of their opposites, rather than any particular quality. Something is genuine if it isn’t a fake: what it is to be a fake is clear. A decision is free if it isn’t forced: if it wasn’t influenced by external factors we would think of as constraints, restraints, threats, and other undue influences? If it wasn’t forced, it was free. Some people find that unsatisfying, but that’s how the concepts work.
In summary:
Were our lives set out in the instant of the Big Bang? No. A unique solution to the hypothetical Differential Equations of Everything relies on a given end-state, which isn’t given. Only the start state is.
Do we lack free-will because this is a material world? Yes, because free-will as defined by an immaterial soul cannot exist.
Does this mean we are the puppets of our immediate circumstances? No, because the human brain can learn and adapt. Sometimes within the moment of an interaction, sometimes when it is thinking of the wisecrack as it goes down the stairs afterwards, or sometimes a lot later after discussing what happened with someone else.
If you want a puppet of its circumstances, think of a tree. It’s got to put up with whatever happens to it, from the moment the seed hit the ground, to the moment a lightning-induced forest fire burned it down. That’s not having free will.
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