Bill Vallicella writes:
“Surely it is a substantive question whether concrete, mind-independent reality is static or dynamic”
I can’t imagine how the question could be substantive. I take the meaning of “substantive” to be that the universe would be a different place in one version of reality than in another, and I can’t see how that would be.
I believe from the context that what Bill is referring to is these two theories of time:
- The dynamic theory of time, or the A-theory posits that the world is a place with distinct past, present, and future, such that the present is continuously becoming the past.
- The static theory of time, or the B-theory posits that time is an undifferentiated dimension, in which past, present and future are just how we perceive the universe, much like as we travel along a road, we perceive the road behind, the road where we are, and the road ahead.
If the choice between these two theories is substantive, then it must be the case that there would be a real difference in the universe if the A-theory were true versus if the B-theory were true. Is there such a difference?
Well, if the A-theory is true, then the B-theory is also true in the sense that it is an abstraction of A-theory time, where you abstract away the distinction between past, present, and future, viewing the whole of time as an undifferentiated line. Conversely, if the B-theory is true, then the A-theory is also true in the sense that it is an application of the B-theory, where each mind represents the past, present, and future of each point based on where the point occurs in the line of time.
How would the universe be different if the A-theory were true and the B-theory an abstraction vs. the B-theory being true and the A-theory an application? Well, we might say that if the B-theory were true, then things in the past, present, and future all exist equally, while if the A-theory were true, then only present objects would exist. That won’t do, because it doesn’t represent a difference in fact, but only a difference in terminology. Both the A-theorist and the B-theorist agree about the facts of the matter, they merely disagree on how to speak of them. The A-theorist agrees that past objects did exist and that future objects will exist; he just emphasizes that such objects do not presently exist.
Meanwhile the B-theorist agrees that the objects that the A-theorist calls “past” are in fact not present in the section of time that the A-theorist calls “the present”, and similarly for future objects. Consequently, there is a direct mapping from A-language to B-language and an inverse mapping from B-language to A-language, so that they are merely describing the same thing in different words. A similar argument can (I claim) be constructed for any difference in descriptions.
But Bill adds another comment that might lead us to a real difference:
Is temporal passage real or is it mind-dependent?
Is there a substantive question of whether time is mind-dependent or not? I say “no”, on the grounds that both theories of time imply that time is mind-independent. Clearly, if the A-theory is true, then the past, present, and future are mind-independent facts of the universe which the mind perceives. I’m not sure what it would mean for an A-theorist to think that time itself (as opposed to the perception of time) is mind-dependent.
If the B-theory is true, then presumably at any point t on the timeline, the mind perceives t as the present, times previous to t as the past, and times after t as the future. How can this be considered mind-dependent? It is just asserting that the mind, at each point in time, possesses a correct perception of its position on the timeline. One might counter that the mind also possesses a sense of the passage of time, which is mind-dependent, since time is not actually passing, but this is just another way of saying that the mind is aware, at each point along the timeline, that there are points in the past which the mind in the past perceived as the present.
I suspect the notion of time being mind-dependent is an artifact of A-theory minds trying to take a B-theory perspective, and inadvertently relying on an A-theory concept while doing so. In particular, I think the idea is that the mind is a sort of focus traveling along the B-theory timeline, viewing it’s current location at each time as the present. But of course, if the B-theory is true, then there is nothing moving along the timeline since the timeline is static. Such a notion requires a sort of meta-time, which reintroduces all of the problems that the B-theory was supposed to deal with.
So, I think the notion that there is any substantive difference between the A-theory and the B-theory is very dubious. Anything that an A-theorist believes about time can be translated into something that a B-theorist believes about time and vice versa, which makes the debate seem more like a terminological dispute than a substantive one.
Brain Legions 