Are Libertarians Armchair Physicists?

A criticism often levelled against libertarians is that they are doing armchair physics.  Take Ted Sider's slogan for libertarians I mentioned earlier here at the blog: "I know from my armchair that physics is incomplete!"  But is this criticism fair?

Libertarians do say that determinism is false.  That much is clear.  But what isn't clear is whether determinism, in this context, is the sort of thesis that could be shown true or false by physics.  When libertarians deny that we live in a deterministic world, their formulation of determinism typically involves notions like the past, the laws of nature, causation, and logical entailment.  Are these notions that would show up in formulations of determinism given by physicists?  Could there really be empirical data to support claims about a logical entailment between two states of the world, given the laws of nature?  In other words, is the sort of determinism denied by libertarians a philosophical (rather than a scientific) thesis?  And if so, is it really fair to call libertarians armchair physicists?

In raising this question, I have in mind a parallel from the philosophy of time.  A criticism often levelled against presentists (those who believe, roughly, that only present objects exist) is that their view is inconsistent with the pronouncement we get from the special theory of relativity that there is no notion of absolute simultanaeity.  But in his article, "A Defense of Presentism", Ned Markosian responds to this charge by pointing out that there are two different ways of understanding the special theory of relativity.  If we understand the theory robustly enough so that it includes the claim that there is no such notion of absolute simultanaeity, then we have reason to think that version is false, since this is a philosophically rich interpretation that goes beyond what the data strictly warrant.  On the other hand, if we understand the theory so that it doesn't include the claim that there is no such notion of absolute simultanaeity, then we have reason to think this version is true, but it doesn't pose a threat to presentism anymore.

Is something similar happening with the attack on libertarianism?  Could it be that any interpretation of the empirical data that includes the claim that determinism (in the philosopher's sense) is true is going too far beyond what the data actually warrant?

Comments

[Eddy Nahmias]

May I turn around your (very interesting) question to ask if determinism is a thesis that cannot be shown true or false by physicists, then what, if anything, could show it to be true or false? (I'm not taking the verificationist line that if it can't be shown true or false by science, then it is meaningless.) Would it be possible, for instance, to find out--on the assumption that incompatibilism is true--whether we have free will?

I've got a somewhat related question: If we take determinism to mean "Nec.[If Past & Laws then Future]", what is it that makes determinism true in a universe? Is it in the nature of the laws (i.e., because the laws are deterministic, the formula above is true) or is it a brute fact about some universes but not others or what?

[Fritz]

Eddy asks:

"If we take determinism to mean "Nec.[If Past & Laws then Future]", what is it that makes determinism true in a universe? Is it in the nature of the laws (i.e., because the laws are deterministic, the formula above is true)...?

The short answer to this is, I think, "yes". I hedge only because I don't really know what "in the nature of the laws" means.

Speaking loosely, the standard definition you cite for Determinism is a statement of what it is for D to be true at a world. D is true at a world just in case:

D1. {Past of the world} nomologically necessitates {future of the world}.

This formulation displays the metaphorical idea of the laws "operating on" the state of the world at one time and transforming it to the state of the world at the next time. If the particular transition that happens *must* happen given the laws (nomological necessity) we are in a deterministic world. (a world with one future broadly consistent with the past and laws of the world).

The formulation above (D1) is *equivalent* to:

D2. [Past of world & Laws of world] metaphysically necessitate {future of world}

which is the formulation one most often sees in these discussions.

That's quick and a bit sloppy, but perhaps helpful despite that.

**
The epistemology of determinism and the question about whether science (or physics, or philosophy or ...) might show it to be true, or false, are ones I'll leave to others for now.

[Alan]

Regarding Markosian's defense of presentism against SRT theory:

But this Markosian-like strategy (I'm not sure Markosian himself would put it this way--he only seems to invoke an alternative SRT as a logical possibility, not as a strong reason to reject standard SRT) is a retreat to 19th century Newtonian/Lorentzian dynamical (real) explanation of Michelson/Morley phenomena relative to some absolute frame of space and time--and there is nothing to support the belief that such absolute frames exist (though I'm ignoring general relativistic rotational phenomena, for example). Since standard SRT works with minimal assumptions (laws are same for all observers; c is a constant for all as well--and the latter collapses into the former), and these only imply relative simultaneity, and one of those is based on empirical observation itself (Michelson/Morley experiments), it's difficult to see this use of Markosian's point as a forceful one. Presentists only whistle in the dark on this point. I decline to infer anything about indeterminists from this.

[John Sorensen]

I am finding it difficult to understand the problems of the relativity of time.
To my thinking, it is the perception of the passage of time that is relative to the observer, whereas the moment "now" is universally present with all events being simultaneaous, even if different observers perceive the events to have happened at different times (or a series of "nows" happening at apparently different rates). The elapsed time between "now" and "now" may be one second to me, where to one travelling slowly it may be one year, but that is only our perception of the infinite number of the durations between these "nows", not that they occurred at different real moments. "Now" is not relative, but it is our perception of the chain of "nows" that we remember, which is relative.
Have I missed where this distinction is explained? As an ameteur, I have not come close to reading everything on the subject, but I have not seen this addressed.