The Man Who Grew Young

(ISBN 1893956172 ) A GraphicNovel by DanielQuinn (Illustrated by TimEldred?)

Question: What's going to happen when the universe winds down to the end of its string?

Answer: Like a cosmic yo-yo, it's going to start winding its way back up the string, to its beginning,—and every life that has ever been lived will be lived again: in reverse.

StephenHawking used to believe that this was the case, but has apparently since changed his mind.

Actually, isn't this what's already happening? Isn't that why we remember the past, like looking in the rear-view mirror of a car, rather than remembering the future, like looking out the windscreen?

Interesting thought. Although I'm not sure if this is more plausible than actually having lived before and simply remembering an actual past.

The realist in me needs to comment. Just like the theories of time travel. Nice thoughts, or entertainment for the imagination, but not so.

[Hawking should have known better from the start. There are a number of different ways to define "the arrow of time". Early in the 20th century, it looked as if the laws of physics, both Newtonian and quantum, were time invariant, which inspired a lot of writing. By mid-20th century, it had been discovered that this wasn't quite true. You have to look at the combination of charge, parity, and time (CPT), and the laws of physics are almost, but not quite, CPT-invariant, thus if our universe were running backwards, in principle we could deduce this relative to our current time arrow.]

[Furthermore, arguably the most important arrow of time is the one defined by modern thermodynamics: statistical mechanics, which is based on information theory, and defines entropy in terms of the number of occupied states in the system. This arrow of time means that it is exceedingly improbably, statistically, for macroscopic events to run backwards. If a teacup falls on the floor and breaks, the odds that random thermal motion will cause the fragments to bounce off the floor and perfectly reassemble on the table are something absurd like 1 chance in 10 to the trillion-trillionth power. That doesn't mean it's impossible, but it does mean that the universe would in general behave differently if the arrow of time ran backwards rather than forward.]

[It has always been unclear to me why Hawking did not take those two arrows of time into account when he originally made his statements about the ultimate cosmological reversal of time; they will not reverse, for the above reasons, even if the cosmological universe does in fact ultimate collapse in something that looks roughly like a reversal of the Big Bang. And this was known, although not widely appreciated, before Hawking started college. (It's probably still not widely appreciated, for that matter.) -- DougMerritt]

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