I explained presentism to my 11-year-old daughter. I told her that according to presentism past and future events aren't real and reality is three-dimensional. She found this view scary. It made her think we live in something like a "flat world", something akin to a "two-dimensional" world. I take it her worry was that this impoverished the world, in much the way that denying a spatial dimension would. Her emotional reaction to presentism is much like mine is: presentism contracts the world to something way too thin.
My daughter then connected this with Zeno's paradox of the arrow. I think her thought might have been something like this: The eternalist can say that movement is what happens in virtue of the arrow being in different places at different times. But according to the presentist, the arrow is where it is, and that's that: that's all of reality. So presentism denies real change (which is ironic since presentists are largely motivated by the idea of saving change).
Now all this isn't entirely fair to the presentist. The presentist does not deny that the arrow was elsewhere and will be elsewhere. Still, "was" and "will be" are operators akin to modal ones like "can be". The fact that the arrow was elsewhere is related to the fact that the arrow is here in something like the way that the fact that the arrow could be elsewhere is related to that fact. Being in different places at different times ends up being akin to one's position being contingent. And that doesn't seem to do justice to the reality of motion. This is all suggestive, though it's probably not much of a knockdown argument.
11 comments:
"Her emotional reaction to presentism is much like mine is: presentism contracts the world to something way too thin. "
Do you have a similar emotional reaction to actualism as well? :)
I really don't think we should consider the present to be a "slice". The world exists, and undergoes changes. The changing world includes moving objects, who are no longer where they used to be, but are now somewhere else (the arrow is in someone's chest; not still on the bow). I wonder if you and your daughter (and others with similar intuitions about presentism) have given similar thought to what B-theory looks like. It looks like nothing ever happens! Reality is a painting, instead of a movie. That, to me, seems like a much less appealing picture. All the suffering that has ever occured, all the people that have ever lived, all the debates... they're all just unmoving, unchanging, frozen parts of a picture that has always been exactly the way it is.
I'm also puzzled as to how the eternalist can say "movement is what happens in virtue of the arrow being in different places at different times". Nothing "happens" at all on the eternalist picture! The eternalist should say "movement is what we call it when an object exists in several different points of spacetime" which is very much akin to how they would describe "size", and which doesn't do justice at all to what we think motion is. Motion is supposed to change something. On the eternalist picture, nothing ever changes from the 4-dimensional perspective.
I also don't think the present is like a possible world, since possible worlds are like snapshots and are not causally contingent on each other; whereas a snapshot of the constantly-changing present would be nothing but a blur (all becomings and no beings), and each present fact is utterly causally contingent on the past facts.... I guess these are probably all just my intuitive gut-feeling, so they're not worth much. But, I do find it interesting that different folks can have such different gut-feelings!
Sure there is change: change is just something being one way at one time and another way at another. :-) Don't we agree that that's a logically necessary and sufficient condition for change?
Our intuition is not that change means "being one way at one point on a dimensional line and another way at another point on that line". That's out intuition of "shape". Our intuition of "change" is that something stops being one way and becomes some other way. If it is a static worm that never actually stops being any way nor becomes any new way, then our intuition of change seems to be completely unsatisfied.
To make my point clearer, consider the comparison you made before, of divesting reality of one of its spatial dimensions. This would indeed be just like removing the temporal dimension line, if B-theory is true. So, imagine talking to a Flatlander (a two-dimensional object) about the third dimension, and saying that it is time. You then tell him that all objects are extended along that third dimension as well, and that "change" just means being shaped differently at one point on that third dimension line than you are at some other point. The Flatlander would probably think that wasn't anything like what they meant by "change". And whether we call the third dimension a temporal line or a spatial line, it doesn't seem to make much difference. I think it is the same way with the 4th dimension (or the 11th, for that matter). Differences in an object along a dimensional line are just aspects of its unchanging shape.
It's not just any line. It's the time line.
Don't you agree that being one way at one time and another way at another time is necessary and sufficient for change?
It's only the time line arbitrarily. It's just a line. Being eternally shaped a particular way along any number of coordinates has nothing to do with change. Change would be if I could stop having my particular 4-dimensional (or 11-dimensional, or n-dimensional) shape, and take on some new shape. But, no, being eternally shaped a certain way along some particular coordinate, even if we arbitrarily call that one the "time" coordinate, is not what anyone means by "change".
It would be like arbitrarily calling the x-axis the "time" coordinate, and the 4th dimension could take on the role of "length", and then it would be true that this baseball bat is changing because it is bigger on one end than the other.
Why think the distinction is arbitrary? In physics and in causation, time seems to play a different role from space.
I suppose we could go into what I think about how physics treats time. I genuinely think the work of people like Tim Maudlin, Quentin Smith, and even William Lane Craig, if paid attention to, will lead physics to re-embrace temporal becoming and the A-theory (it solves lots of problems with Relativity and QM at zero cost).
And we could talk about causation, which I think is rather problematic on a B-theory where every effect and every cause co-exist simultaneously. And are separated from each other only in the way one end of the baseball bat is from the other end (and surely, despite the counterfactual truth that "if this end didn't exist, then neither would the other", still no one wants to call one end of the bat the cause of the other end!).
But, I think just focusing on "change" is the key for the moment. "Change" intuitively means to stop being one way and begin being some other way. On an eternalist view, this never occurs. You can say that "being one way at one time and another way at a later time" is sufficient, but you are not using the word "time" the same way people intuit it. People intuit that one way of being has ceased to be the case and has been replaced in reality by a new way of being. That is what "change" means. That is why we understand immediately what I mean when I ask "could the 4-dimensional shape of events change from being the way it is to being some other way?", and we understand it without thinking there is some secondary timeline along which the 4-d spacetime is shaped different from one point to the next.
Am I making sense? Are you not sympathetic to the idea that 4-d shape differing from one point to the next is not at all what people mean by an object changing?
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