Posts on: Time
Here's an attractive picture. All there really is, at a fundamental
level, are fields in spacetime (or something like that). The world as we
know it, with its rocks and chairs and cats and people, somehow emerges
from this basis: all truths about rocks and chairs etc. are made true by
truths about fields in spacetime. But how? To explain this, it would
help if we could locate the familiar objects – rocks and chairs etc. –
in the physical description of reality. With the help of classical
mereology, which is plausibly analytic, this
seems possible: ordinary objects can be identified with aggregates of
spacetime points. They are regions in spacetime. With this, we can
explain how simple facts involving ordinary objects can emerge. For
example, what makes it true that my chair has steel legs is that its
region has a certain kind of subregion with high-amplitude excitations
of quark and electron fields in a certain arrangement.
I've been reading Fabrizio Cariani's The Modal Future (Cariani (2021)). It's great. I have a few comments.
This book is about the function of expressions like 'will' or 'gonna' that are typically used to talk about the future, as in (1).
(1) I will write the report.
Intuitively, (1) states that a certain kind of writing event takes place – but not right here and now. 'Will' is a displacement operator, shifting the point of evaluation. Where exactly does the writing event have to take place in order for (1) to be true?
Here's a natural first idea. (1) is true as long as a relevant writing event takes place at some point in the future. This yields the standard analysis of 'will' in tense logic:
Here's something puzzling. Suppose sometime in 1869, Frege uttered
1) more people today die of tuberculosis than of cancer.
As far as I know, this was true in 1871, but it is no longer true now. Today, more people die of cancer than of tuberculosis. On the other hand, suppose Frege also uttered
2) I am not particularly well-known among philosophers.
This, too, is no longer true. Today, Frege is exceptionally well-known among philosophers.
Suppose some thing x turns F, and a little later some other thing y turns G. x is the only F throughout history, so on a Humean account of laws of nature, it may well be just a coincidence that y's being G followed x's being F. Suppose it is.
But now consider another world just like this one except that in the far future, lots of G-turnings follow lots of F-turnings so that in this world, it is a law that whenever something turns F and another thing is suitably related, then that other thing turns G. In such a world, x's turning F caused y's turning G.
A time traveler convention will be held at MIT on May 7. Apparently the organizers have in mind a branching universe model of time travel, otherwise this makes no sense:
Can't the time travelers just hear about it from the attendees, and travel back in time to attend?
Yes, they can! In fact, we think this will happen, and the small number of adventurous time travelers who do attend will go back to their "home times" and tell all their friends to come, causing the convention to become a Woodstock-like event that defines humanity forever.
Anyway, suppose no time travelers from the future show up at the convention. Does that decrease your credence in the physical possibility of time travel? If so, would your credence decrease by the same amount if the convention was (now) set to take place in the past, say on May 7, 2004? After all, there's little point announcing a time traveler conference in due time before the event.
I'm somewhat stuck with the parts/counterparts paper. One of the problems is to find an acceptable semantics for time travel situations.
Part of the problem is that I'm often unsure what to say about these cases. I guess if time travel were more common, we would need some new linguistic conventions. Anyway, here are some sentences that seem true to me in the following scenario: Tina decides in 2025 to meet her younger self back in 2005. So at some time t in 2005, the younger Tina is in the living room and weighs 60 kg while the older Tina is in the kitchen and weighs 70 kg. Now, these all seem true to me:
There are two ways of denying that the future is real. One is to accept statements about the future as true but to interpret them in a way that does not require the existence of their subject matter. This is a kind of fictionalism or ersatzism about the future. (It's interesting by the way that abstract ersatz futures clearly don't count as futures, whereas it is controversial whether abstract ersatz worlds should count as real possible worlds.) The other way of denying the reality of the future is to reject the assumption that statements about the future are true. Then no fictionalist or ersatzist story needs to be told to account for their truth.