Hello all.
Since it's Friday night and we don't yet have a blog post on Putnam, let me just ask you all to share your thoughts.
Putnam argues that the relativity of simultaneity in special relativity resolves one of the major problems of time. It shows, he argues, that the future is just as real as the past and present. Here's a short, rough version: There are no privileged observers. So if being real is determined by some spacetime relation, it must be a relation not to me but to "an observer". Now suppose that relation is: being in the present or past of the observer. There are observers in my present and past, so they are real. Events in their present and past are also real, because such events are in the present or past of "an observer". But some of those events are in my future! So events in my future are real. And by chains of observers, all events in my future are real.
In the lecture I briefly reviewed Sklar and Stein's alternative views. In short, Sklar suggests that 'real' might be relative and intransitive, while Stein separates 'real' from 'present' -- in fact, he proves that if 'real at' *is* transitive, and something in the past light cone of an event is real at that event, then all events in that past light cone are real at that event. So Stein's (noncommittal) suggestion is that all and only those events in the past light cone of an event are real at that event, and the simultaneity hyperplane doesn't enter into it.
So what do you think? Does Putnam's argument hold up? Where exactly does it fail?
My intuition is that Putnum's conclusion is correct with or without SR.
ReplyDeleteNevertheless, I suppose that the minimum that Putnam shows is that the SR is inconsistent with the two doctrines taken together that: (a) either the past or the future or both are not real and (b) that what is real for a real observer is real. NB observer refers to an observer at a particular time. Given this, Putnam gives no reason to reject (a) over rejecting (b), so doesn't quite prove what he says.
Regardless of this, I think that one certainly should reject (b) simply because `realness' is just not the kind of thing that could be relative to particular observers---to suppose so would be to make a mistake as to what it is to be real.
Also relativity of realness leads to the objectionable conclusion that events spacelike separated from an observer are not real for that observer, which is very counter-intuitive for me.
I also think that the argument is convincing in showing that special relativity together with the no privileged observer claim and an absolute concept of realness excludes dynamical views of time.
ReplyDeleteI think, neither the no privileged observer claim nor special relativity, of course, are controversial. What makes Putnam's argument so appealing is that it rests on only few premises for this strong conclusion: The only thing left to reject the argument seems to be the notion of relative realness. Then the inference of transitivity from the no privileged observer premise collapses.
That is what Sklar does. I am not sure I agree with Jon though that such a relative notion of realness is really that bad. Or I should rather say, I am not sure the reason you give is convincing.
Realness is probably not an entirely well defined concept the way we use it. Also, we might be using it in a wrong way, just like in the case of "absolute motion" according to special relativity. So we might have to do more philosophy in order to adequately assess the idea of relative realness. It might turn out to be a bad one, of course, I don't know. I agree that it does not look too attractive, it has a bit of an unpleasant relativistic flavour (the unintuitive unrealness of spacelike separated events just reflects this).
Actually, I don't really understand why that last thing is, why spacelike separated events are not real for an observer. That sounds like what Stein suggests, which seems to be only a specific notion of relative realness, namely one relative to an event. But does it follow from relativity of realness with respect to an observer? Then everything on or below the observers simultaneity plane is real, which could include several different light cones.
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