Time Metaphysics 2019

Time Travel: One More Time

Draw on the Board!

Time & Space According to modern physics, space and time are one thing: spacetime. Time is just a further dimension, like the three dimensions of space.

Time & Space Think of it this way: If you want to set up a meeting with someone, you have to give them four co-ordinates: the meeting’s location in space and its location in time.

Differences between Time and Space Space doesn’t have any rules about what comes next to what; time does have rules. You can freely travel any direction in space, but only one direction in time.

Time’s Arrow There are asymmetries in time that don’t exist in space: You can remember the past, but not the future. You can cause future events, but not past ones.

Eternalism

Tenets of Eternalism Past, present, and future all exist equally and in the same sense. There is no privileged “present” moment; every past, present, and future individual experiences their time as “present.” The only temporal notions we need are before, after, and simultaneous with.

No Privileged Present There is no objective “here” in space. Each person is “here” for themselves. Likewise, in time there is no objective “now”, according to eternalism. Each (time slice of a) person is “now” for themselves.

J.M.E. McTaggart (1866-1925) British idealist philosopher Trinity College, Cambridge His place in history

McTaggart against Eternalism McTaggart thought that eternalism was not a theory of time, because it didn’t involve change. Things exist at “times” then other things exist at other “times” but no thing moves through time or changes.

McTaggart on Change Eternalism tries to make do with the relational notions: before, after, and simultaneous with. But McTaggart thinks any real theory of time must include: past, present, and future. Change is something’s being future, then being present, then being past, then being more and more in the past.

The A Theories

McTaggart against Eternalism McTaggart called before, after, and simultaneous with the “B properties” and past, present, and future the “A properties.” Any theory of time that contains a privileged present is called an A theory of time.

Presentism The simplest A theory is presentism. According to presentism only the present exists. Dinosaurs used to exist and next week’s class will exist, but now they don’t exist.

The Growing Block Theory According to the growing block theory, the present exists and the past exists on equal footing, but the future does not exist (yet).

The Moving Spotlight Theory According to the moving spotlight theory, there is a block universe, just like on eternalism. However, there is also a privileged present. The moment that is present moves through the block like a spotlight sweeping across the ground.

McTaggart against A Theories McTaggart thought that time was unreal, so he argued against both eternalism and the A theories. His argument against A theories accuses them of requiring an infinite regress of higher-order temporal properties.

Infinite Regress Consider the event: Michael receives top marks in his student evaluations. This successively has the properties: Future Present Past

Infinite Regress But nothing can be both future and past. Nothing can be both past and present. Nothing can be both… you get the point.

Infinite Regress Resolution: the evaluations: ARE in the future WILL BE in the present WERE in the future WILL BE in the past

Infinite Regress Resolution: the evaluations: ARE in the future WILL BE in the present WERE in the future WILL BE in the past

Presentism

Presentism According to presentism only the present exists. Dinosaurs used to exist and next week’s class will exist, but now they don’t exist.

Common Sense Intuitively, (non-avian) dinosaurs don’t exist. Presentism says the past and all things in it don’t exist. So win for presentism.

Contra Presentism: The Semantic Argument BUT! If dinosaurs don’t exist… not even in the past, which also doesn’t exist… what are we talking about when we talk about dinosaurs?

Contra Presentism: The Grounding Argument The presentist says now it is true that dinosaurs used to exist. But many philosophers think that for something to be true, there needs to be something– an object, a fact, whatever– that makes it true.

Contra Presentism: The Grounding Argument The problem is that it’s hard to point at the thing in the present that makes it true that dinosaurs used to exist. What’s the difference between our world where dinos did exist and one where they didn’t?

Contra Presentism: Special Relativity But the biggest argument against presentism is that it seems to be inconsistent with modern physics. There is no privileged present.

Special Relativity

Brian Greene Professor of physics and mathematics at Columbia University

Video Time! https://www.youtube.com/watch?v=H1WfFkp4puw&t=937s

Things to Talk about Sharing motion metaphor Now/ bread slices The Andromeda paradox Rietdijk-Putnam argument Presentism

Temporal Asymmetries Redux

Time-Reversal Invariance According to the basic laws of physics, processes that run in one direction can just as sensibly run in the other.

Video Time! https://www.youtube.com/watch?v=mGDJO2M7RBg