Universe Today
This is Part 3 in a series on the physics of free will. Check out Parts 1 and 2.
So let’s say you set up an experiment to measure a quantum property of subatomic particles. Like, I don’t know, spin. All fundamental particles have spin, and even though they’re not actually tiny little spinning balls we still pretend they are because the quantum world is weird and we don’t have a lot of experience with it so we tend to reach for the nearest analogy we can find and then it just kind of sticks even though it doesn’t make much sense but then again nothing really makes sense about quantum mechanics.
Slow, deliberate exhale.
Here’s the thing. You run a quantum experiment, and you don’t get to know the answer ahead of time. It’s all random, all probabilities, all wave function this and Born rule that.
Oh, and the Heisenberg uncertainty principle? You know, the one that says we can never know precisely both the position and momentum of a subatomic particle? Well there goes any hopes of circumventing chaos theory by finding cheat codes to give you perfectly precise measurements. The HUP guarantees that you never will, so that’s nice.
So can we find the origins of free will in quantum uncertainty? Eh, kinda yes, kinda no, depending on how you want to take this.
For one, quantum mechanics is still a theory of physics, which means it’s still based on causal determinism. We just need to be careful about what we’re determining. In QM, effects still have causes, event A still leads to event B. Nothing happens FOR NO REASON. There are still laws of physics that govern the evolution of systems and allow us to predict what will happen in the future.
But what QM messes up is our ability to PRECISELY predict what will happen in the future. We can instead only assign probabilities to various outcomes. You go to measure quantum spin of a subatomic particle, you get a 50/50 shot of either getting spin-up or spin-down. It won’t be spin-sideways or spin-double. And it won’t be 1% spin-up vs 99% spin-down. We CAN make a prediction: you’re going to get either spin-up OR spin-down, and you have an equal chance of getting either.
We can’t say which one you’re guaranteed to get, but we can assign the probabilities and make calculations. We can still predict the future, and rest assured that causes lead to effects and the normal ordering of the flow of time make sense and all that, we just have to insert a little bit of quantum fuzziness when we’re talking about quantum systems.
And then there’s the whole correspondence principle. Quantum mechanics doesn’t exist in a vacuum. It’s a part of the wider universe of…uh, the universe. We use quantum rules to understand quantum systems, which are almost always subatomic systems. We don’t use quantum rules to describe literally everything else happening in the universe. If I throw an electron at you, quantum mechanics. If I throw a baseball at you, normal physics.
There must be a correspondence between these two realms. And that correspondence is governed by the…correspondence principle. It basically says that yes you can use quantum mechanics for quantum systems, but once you get a lot of particles together to make macroscopic objects, you’re going to have to switch over to regular, not-quantum-at-all physics.
And this isn’t just some nice idea. It’s baked into quantum theory. When we first started encountering quantum systems, we had to idea what to use to guide our thinking in deciding what laws and rules apply and what don’t’. The correspondence principle helps us: if you want to make a quantum theory, then you better make sure that it recovers normal physics when you get to normal systems.
But when and how this changeover from quantum to normal physics takes place is a bit of a unknown. So if the inner workings of our brains, especially the generation of decisions, lays firmly in the quantum realm, then there may be some aspect to free will that can never be predicted. But since we strongly believe that the correspondence principle is true (and we have no reason to doubt it), and brains are obviously macroscopic objects, it could be that quantum mechanics has absolutely nothing to say about free will at all, and this is all just a red (quantum) herring.
I do have to mention that there may be a way to get rid of all the quantum probabilities. That’s through a concept called super-determinism. We usually think of quantum experiments from two sides: there’s the quantum side, usually involving subatomic particles, that do whatever the heck they want. And then there’s us, the observers/experimenters/measurement-makers, who are not quantum objects at all and have things like free will.
The extremely short version of superdeterminism that we are all quantum systems, all entangled and interconnected with each other. And instead of random events, the entire quantum state of the universe evolved from a highly specific set of initial conditions to lead to a precise experimental outcome, predetermined outcome. In other words, you can get rid of the randomness of quantum experiments if you find a way for the universe to have no other choice but to lead to that result.
Superdeterminism is not that well regarded, because it opens up a lot of nasty, unanswered questions, like how in the world did the entire universe’s initial state be so perfectly finely tuned to give me this result, and even our very existence, instead of just a morass of jumbled incoherence? Also it kind of destroys all of science: we don’t “learn” anything about the universe by running experiments because the outcomes are all predetermined.
But it also destroys free will at a quantum level, which is nice if that’s the kind of thing you’re going for.