Thursday, August 13, 2020

Relativity and an argument for incompatibilism

A common argument for the incompatibility of freedom and determinism goes something like this (where premises 1, 2 and 3 are implicitly assumed to hold at all times):

1. It is currently possible that I will do A only if the past and the laws are compatible with my future doing of A.

2. If determinism is true, then the past and the laws are only compatible with my future doing of what I will in fact do.

3. So, if determinism is true, the only things that it is currently possible that I will do are the things that I will in fact do.

4. Freedom requires that at some time it be possible that I will do something other than what I will in fact do.

But given relativity theory, it is not clear what “the past” means in the above arguments, since past is always relative to some reference frame. There are at least four ways of reading (1):

• Strongest: It is now possible for me to do A only if the events in the complement of my present closed future light-cone and the laws are compatible with my doing A.

• Stronger: It is now possible for me to do A only if for every reference frame R, the past according to R and the laws are compatible with my doing A.

• Weaker: It is now possible for me to do A only if for some reference frame R, the past according to R and the laws are compatible with my doing A.

• Weakest: It is now possible for me to do A only if the events in my present open past light-cone and the laws are compatible with my doing A.

Now, generally we should prefer less strong premises. So we should avoid the Strongest and Stronger readings of (1). But I claim that the analogue of (2) is unjustified if we take the Weaker reading of (1). For suppose A would be a future action. Then the past open light-cone of A will be strictly larger than my current past open light-cone. Determinism tells us that A or its absence is nomically determined by the events in its past open light-cone. But that past open light-cone is strictly larger than my current past open light-cone. And it could be that some event E that is in A’s past open light-cone but not in my current past open light-cone makes a difference as to whether A happens. Then there will be a reference frame R such that this event E would be outside my current past according to R. Thus, A’s or its absence’s being determined by the events in its past open light-cone leaves open the possibility that some event E that isn’t in my current past according to R makes a difference as to whether A happens, and hence that A or its absence need not be determined by the events in my current past according to R.

So, for the argument (1)–(4) to work given relativity, it seems we need the Stronger or Strongest reading for (1).

Is there a better way to fix the argument relativistically? Maybe. I like the idea of replacing (1) with an atemporal formulation:

1. Action A is only free if its non-occurrence is compatible with the laws and the subset of events in A’s causal history that are outside of my life.

David Alexander said...

Hi Alex,

I think a number of folks who write about this are starting to recognize a number of difficulties with fixity of the past principles. I am working on a few papers that attempt to poke some holes as well, and one that tries to show that Ockhamists should seriously consider some of the moves that Thomists (and others who hold to divine simplicity) need to make.

Andrew Law has a really nice paper coming out in Phil Studies, where one of the arguments he gives is almost exactly what you give above. He prefers the following to the standard Fixity of the Past Principle.

Fixity of the Independent: Agent S can perform action X at time t (in world w) only if there is a world, w’, such that all of the facts in w that are distinct from and explanatorily independent of the facts constituting S’s behavior at t hold in w’ and S performs X at t.

If I am understanding it correctly, I think this is very close to what you offer at the end of your post.

Alexander R Pruss said...

David:

One potential worry with switching from causation to explanation is that some people think final explanation runs in the opposite direction to causal explanation. Another worry is that on Humean views, the laws of nature are non-causally explained by the sum total of all physical events, including S's behavior, so the principle wouldn't require that w' have the same laws, since the laws aren't distinct from and explanatorily independent of S's behavior. We get out of both worries if we restrict to causal explanation. (We also get out of both worries if we have the right views of final explanation and of laws, but it would be better not to have to rely on that.)

Alexander R Pruss said...

It is worth noting that in my hierarchy of five principles, Law's is something like my Strongest.

Andrew Dabrowski said...

I am not a physicist, but my understanding is the light cones are invariant w.r.t. different observers. And only events in a time-like relation can be causally related. So despite relativity there is no ambiguity about whether events can be causally related.