# Temporal thermodynamics

1. Dec 1, 2003

### jackle

Not sure where to post this. You can move it if you like.

There is no right answer to this but I hope it makes you think as
much as it made me think.

A long time in the future, man-kind can travel backwards in time by
breaking the light barrier. The research team calculate that according
to Einstien's equations, they will trace a smooth path through
space-time as they are travelling backwards through time. The same
set of events can be viewed form inside and outside the ship. They are
however, curious as to what happens if they drop one of the glasses

According to the 2nd law of thermodynamics, the glass drops then
smashes as time goes forward. This gives rise to a simple paradox.
Which way is forwards?

If the second law is obeyed in the reference frame of the space ship,
the on-board team experience nothing unusual, but the rest of the team
on the ground will see the same events, but to them, the glass is
smashing, then rising from the floor! Events aboard seem to go
backwards from the reference frame of the GROUND team.

To correct the paradox, the ground team argue that the second law must
be obeyed in the reference frame of the ground team, now they would
see it the right way round. BUT the on-board team complain
that they would experience the glass smashing, then rising from the
floor as they travel backwards through time! Events aboard seem to go
backwards from the reference frame of the ON-BOARD team.

Only one can be correct. The two teams place a bet. Who wins and why?

Last edited: Dec 1, 2003
2. Dec 1, 2003

### chroot

Staff Emeritus
Simple. Nothing can go faster than light, and thus time-travel to the past is impossible.

- Warren

3. Dec 1, 2003

### jackle

Yes

I quite agree, but did you think it through?

4. Dec 1, 2003

### chroot

Staff Emeritus
Re: Yes

- Warren

5. Dec 1, 2003

Imagine...

6. Dec 1, 2003

### chroot

Staff Emeritus
Imagine what? Shall I also imagine that 1 = 2? And left = right?

- Warren

7. Dec 1, 2003

### jackle

Yes! Anything to expand the mind! Please!

8. Dec 1, 2003

### chroot

Staff Emeritus
The real world is much more fascinating than any imagined.

- Warren

9. Dec 2, 2003

### Mentat

Well, jackle, if it's not enough for you that we can never end up in a situation where this problem would become relevant, then perhaps the fact that reality is different depending on your inertial reference frame will help. Basically, the people on the ship are only going backward in time in some reference frames, and not in others.

Also, if I were to drop a glass before having begun traveling backward, then I could logically expect to see the cup "pick itself up" so to speak. However, if I drop it while traveling backward in time, then it will indeed fall, and shatter. Traveling "forward" or "backward" is only relevant when you have to change it.

10. Dec 2, 2003

### Ivan Seeking

Staff Emeritus
Igor Novikov: an essay printed [p57] in The Future of Spacetime; Cal Tech, 2002

Stephen Hawking: p87 The future of Spacetime

11. Dec 3, 2003

### jackle

But either way, will not the same chain of events be viewed in reverse from the ground team? Wouldn't this mean that the second law has to be violated from at least one observer's perspective?