Last week, we had some discussion of free will, which prompted some comments about determinism. I’m not convinced that determinism has all that much to do with free will one way or the other, but since the topic’s been raised, here are a few bullet points, jotted down late at night, which I hope will still make sense in the morning.
- It seems to me that the whole notion of determinism is quite a bit murkier than it first appears, to the point where I’m not at all sure I know what it means — and not at all sure that its defenders have any clearer sense of its meaning than I do. The remaning points will elaborate on this.
- I’ve seen people define determinism as the statement that the history of the Universe could not be anything other than what it is. That, of course, is true, because nothing can be anything other than what it is. If it is a fact that Abraham Lincoln scratched his beard in the East room of the White House on April 14, 1862, then it cannot not be a fact that Abraham Lincoln scratched his beard in the East room of the White House on April 14, 1862. If it is a fact that intelligent fish from the moons of Saturn will land a spacecraft on the Lincoln Memorial on April 14, 2062, then it cannot not be a fact that intelligent fish from the moons of Saturn will land a spacecraft on the Lincoln Memorial on April 14, 2062. So to define determinism this way is to make it trivially true, and hence uninteresting.
- Another possible definition is that the future history of the Universe is a logical consequence of its present state. This (by Godel’s Completeness Theorem) is equivalent to saying that any Univese in the same present state as ours must have the same future as ours.
But I claim this formulation makes far less sense than it appears to, because our Universe has no globally defined “present state”. The “present” is a local concept — and even that is observer-dependent. Now, the observer-dependence is perhaps not such a big problem; you could always formulate determinism to mean something like “The future, as defined by any observer, is fully predictable from the present, as defined by that same observer”. But the larger problem is that no observer has a notion of simultaneity that extends beyond his local neighborhood. (Very simplified cosmological models do incorporate global time coordinates, but I’m pretty sure nobody believes that’s an accurate depiction of reality.) So according to “determinism”, exactly which regions of spacetime are supposed to contain the information necessary to determine the entire history of the Universe? I’ve never seen a clear answer to this, which suggests that nobody has given a really coherent description of what determinism is.
Edited to Add: Roger Schlafly points out in comment #1 that one doesn’t need a global time coordinate to define determinism; one only needs a spacelike hypersurface, which might or might not be a surface of simultaneity for some observer. Point taken, and this largely dispenses with my objection here.
On the other hand — does “determinism” mean that there exists a spacelike hypersurface that completely determines the history of the Universe? Or that there exists a family of spacelike hypersurfaces that cover all of spacetime and any one of which determines the history of the Universe? Or that any spacelike hypersurface completely determines the history of the Universe? It still seems to me like there’s some fuzziness here, though I now think it’s much more likely that this fuzziness has been addressed somewhere.
- In any event, even if you take a very local notion of determinism, it’s pretty definitively ruled out by the Aspect experiments, for reasons I’ve described in Chapter 16 of The Big Questions. More precisely, the results of the Aspect experiments force you to abandon either determinism or Lorentz invariance (i.e. special relativity), and even if you think it would be crazy to abandon determinism, it can’t be as crazy as abandoning Lorentz invariance.
(A third possibility is that Nature is really out to fool us, say by infecting the brains of Alain Aspect and his colleagues so that they consistently choose to observe exactly the wrong thing, or by altering the experimental records — and the experimenters’ memories — after the fact, to create the maximally misleading false beliefs about what actually happened. Is there any determinist so determined that he’s willing to stand on this shaky foundation?)
- The above all ignores the possibility of a many-worlds or many-histories interpretation of quantum mechanics, which can indeed rescue some form of determinism from the Aspect assault, but I’m not at all sure that that sort of determinism has much to do with the determinism of the declared determinists, because it admits that the “present” state of the Universe (whatever that might mean) does not uniquely determine the future state in any given history.
- In any event, what does any of this have to do with free will? Let’s take the most extreme form of determinism imaginable: Suppose it’s the case that there is one and only one Universe, with one and only one history, in which intelligent beings emerge. Thus the entire history of the Universe is a logical consequence of your existence. What light does this shed on the question of whether it’s useful to think of your volitions as causal? And if none, what other relevant question does it address?