When I was in undergrad, I once dined with a philosophy major who spontaneously began to argue against free will (apparently some philosophers like to argue unprovoked). He wanted me to imagine that there is a being [such as a God] who knows classical mechanics perfectly and can calculate anything. Even though the universe is a chaotic system, this great intelligence knows the starting conditions, and can calculate the movement of every particle in the universe (ignoring quantum effects as negligible). This being will be able to know what obstacles you will face (e.g., car coming down the street) and will know how you will act (your reaction time, which neurons will fire, if you will be able to get out of the way or not), and how your reaction will affect the rest of your life. And how it will affect the lives of your children, all of humanity, earth, and beyond.

We had a semi-productive discussion (argument), but his refusal to engage with quantum mechanics bothered me. First, quantum mechanics is not negligible when talking about life, and second, saying “quantum mechanics” doesn’t suddenly mean that the world is random and non-deterministic. Plenty of biological processes rely on quantum mechanical processes, because proteins (and their active sites) are really, really small. And many reactions that happen in the body (like redox reactions) involve electron or proton transfers, which are almost always quantum mechanical in nature. Second, a lot of interpretations of quantum mechanics are pretty deterministic–that is, the Schrödinger equation explains the probabilities of what can happen (and no other options can happen). When the wave function collapses, one of the predicted outcomes will happen. This is pretty deterministic, because nothing gets to pick and choose how things will turn out. They simply happen. Quantum mechanics isn’t necessarily a vote for free will by any means, especially the less popular De Broglie-Bohm interpretation, which is deterministic at its core.

My dining companion’s argument is not new (it bothered Isaac Newton upon his development of classical mechanics, long before quantum mechanics was dreamed up),(1) and it has bothered me over the years. It’s called Laplace’s Demon (where the great intelligence is the “demon”), after Pierre-Simon Laplace formalized his fear of determinism in explicit terms.

There are numerous discussions of determinism vs free will that go into many pages of examples and counterexamples, and I won’t really rehash them here. Some of them describe pretty cool concepts, such as Norton’s Dome so the interested reader should peruse them.

The main question that one has to ask him or herself when thinking about Laplace’s Demon is ultimately, what is the threshold for free will? If it is randomness, you can forget about using quantum mechanics as some hand-wavy crutch.  Temperature can cause particles to behave in basically a truly random fashion. For instance, Johnson–Nyquist noise (electronic noise) is spontaneous and will happen in any resistor, and the higher the temperature, the noisier it will be. It is a random process. But does random noise in a circuit guarantee free will? What about in a human body? Body temperature (98.6 °F, 37 °C, or 310.15 K depending on your favorite units) generates so much thermal noise that the motions of water molecules (of which comprises about 70% of the human body) is completely unpredictable. Considering there are a mol (6.022*10^23) of water molecules for every 18 grams of water, and the average mass of a North American person in 2005 was 80.7 kilograms, there are about 1.8*10^27 molecules of water in the human body. You’ll burn out quite a few supercomputers trying to figure out the trajectory of those molecules over a microsecond, let alone a lifetime. The motions of proteins and tiny molecules in the body is completely stochastic, and mostly random, as a result.

But could someone compute it? Let’s pretend someone has the Schrödinger equation for the universe, and knew how to solve it exactly (which would be pretty cool, because we can’t solve it exactly for anything that has more than one electron, or everything in the universe other than an isolated hydrogen atom). They plug the equation into their fancy computer and hit run. The computer starts chugging. It comes to an event where two particles interact, and could have several possible outcomes. It picks the correct outcome, because it can solve the Schrödinger equation for the universe exactly. Then it has to repeat this process a googolplex more times (or slightly less) before it reaches the present day. Oh. It just simulated the universe exactly if we were living it. It has to go sequentially, just like we live our lives. It can’t magically jump forward 5 months to see if your paper will be accepted into Nature, because each new decision or calculation depends on something that happened before it.

Ultimately, I think that there are two ways of thinking about it. If you’re worried about some supernatural being coming along that will compute your future, and you are an atheist, then that being doesn’t actually exist for you and you have nothing to worry about. On the other hand, If you believe in an supernatural omniscient being, then by definition you already accept that God is all-knowing and could know the future if God chose to do so. This leads to some delightful philosophical thought experiments and paradoxes in it’s own right, such as, can God create a rock so big he cannot move it? Either way, it’s not going to change how you live your life, nor will it affect the choices you make. And that is why you have free will–no one is telling you what to do. Even if some God-like being could predict the future, they aren’t telling you what to do (and if you are hearing voices, you might want to consider seeing a doctor).

Print References:

  1. Stephenson, Neal. “Metaphysics in the Royal Society 1715-2010 (2010).” Some Remarks. New York: HarperCollins, 2012. 38-57. Print.


Feature image in public domain, courtesy Wikipedia.

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