Notes for 11/11/2025

 

11/11/2025

[Philosophy Club every Tuesday at 5:00pm in CAS 436 ("The Cave")]

[Challenge for today: Try to think of (and possibly ask) at least one question.]

 

How fast does time pass?

 

What is time?

 

Time is often compared to space

 

Time line

 

Time is often considered to be symmetrical with respect to past and future

 

Does time have a direction?

 

 

There are different conceptual models of time

 

There are three dominant models of time:

 

1.   Presentism (only the present exists)

a.   The past used to exist but doesn’t anymore

b.   The future will exist but doesn’t now

c.   The present exists, but not for long

(Analogy: novel written in disappearing ink)

 

2.   Fixed past open future (growing block view)

a.   The past is “fixed”. What has happened is a permanent part of history and has as KIND of reality.

b.   The future is open (undetermined). What is going to happen is not yet fixed.

c.   The present exists and is somehow more robust than the past (the past has a kind of ersatz reality)

 

(Analogy: novel written in permanent ink)

 

3.   Block universe or 4-dimensionalism

a.   Past, present, and future are all equally real. All equally fixed.

b.   The “present” / “now” functions like “here” in space.

(Analogy: Novel that is already written.)

 

Is time travel possible?

 

Start at time 1 and end at time 2 where time 1 and time 2 are different. And we are not traveling at the “normal rate.” (what we want from a definition of time travel is a kind of “jumping” from one time to another without “crossing” the intervening time)

 

Presentism (only the present exists) appears to preclude time travel, because temporal destinations different from the present don’t exist.

 

How is motion through time (even at the normal rate) possible if the future doesn’t exist?

 

How is any change at all of any sort possible under presentism?

 

Also, Presentism appears to be empirically false.

 

The concept of simultaneity (NOW) vanishes under special relativity.

 

There is no such thing as THE present.

What is present/now depends on frame of reference.

 

General relativity also conflicts with presentism.

 

The rate at which time passes is affected by gravity.

 

“How fast does time pass?”

 

The falsity of presentism seems to permit the possibility of some kinds of time travel.

 

Causal limitations on time travel

 

A brings about B

 

If time travel is possible into the past, then it would be possible to avoid B by making A not happen.

 

But B is what brings about your elimination of A.

 

Causal paradox (best known example = grandfather paradox)

 

Going into the past to eliminate A results in your only eliminating A’

 

 

time travel into the past might be possible so long as causality is not violated