
Mysteries of time, and the multiverse - nickb
http://www.latimes.com/news/education/la-sci-carroll28-2008jun28,0,6029497,full.story
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mynameishere
_The fact that you can turn eggs into omelets but not vice versa is a thing we
know from our kitchens._

Unless you feed a hen nothing but omelets. Am I right?

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crescendo
What about the hen's mother?

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mynameishere
Given a sufficiently efficient hen, you could feed her her own eggs.

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crescendo
But wouldn't you have to feed omelets to the hen's mother also? Otherwise the
hen couldn't have been born. And the hen's mother's mother, and mother's
mother's mother, and so on, leading back from the final egg.

edit: on second thought, this is probably too much philosophizing.

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xlnt
A hen is a machine which can turn food (including omelets) into eggs. It
doesn't matter where the hen came from. The point is one can build a machine
to do this.

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bayareaguy
A hen interpreter?

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Mapou
Time cannot change by definition. Nothing can move in spacetime for the same
reason. This is why the late Sir Karl Popper (of falsifiability fame) once
compared spacetime to Parmenides' block universe and called it "Eintein's
block universe in which nothing ever happens". (Source: Conjectures and
Refutations).

In his textbook, "Relativity From A to B", renown relativity expert Robert
Geroch wrote, "There is no dynamics within space-time itself: nothing ever
moves therein; nothing happens; nothing changes." Very few physicists know
this but it's the truth, a nasty little truth for some, but the truth
nonetheless.

In conclusion, any talk of time travel in any direction (forward or backward)
is pure crackpottery. There is only the NOW, the ever changing present. Don't
mod me down because you have a different opinion. Incessant propaganda and
sci-fi movies like Star-Trek have duped a lot of people. Just think about it
and figure it out on your own.

Nothing can move in spacetime.

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ajross
You're not explaining that very well. Yes, classic relativity is a
deterministic theory which doesn't have a time arrow. You can look at it as a
single, static universe defined as the sum of all moments. But that's neither
here nor there. Classic relativity is, strictly speaking, wrong: the real
universe is, as far as we understand, provably non-deterministic.

And in any case, it has nothing to do with this article, which is about the
time arrow defined by entropy.

~~~
Mapou
I am not sure exactly what you explained. First off, relativity, like
Newtonian mechanics, is a classical physics theory. I am not aware of any such
thing as non-classical relativity. So why even say classical relativity? At
the very least, it is redundant.

Second, of course the universe is probabilistic, a fact that falsifies both
relativity and Newtonian physics.

Third, the universe is probabilistic precisely because time cannot change.
Why? Because, since time is not a variable and is thus non-existent, the
universe cannot calculate precise temporal durations. Thus, in order to
properly conserve energy, it is forced to use the next best thing:
probability.

Fourth, this has everything to do with article since entropy, as explained in
the text books, assumes the passage of time and thus a time direction or
arrow. Since time is abstract, it follows that an arrow of time is imaginary.
As a result, it makes perfect sense that one cannot reverse entropy. Or
anything else, for that matter.

The purpose of my comment was to get people to think and to stop accepting
everything they hear on face value. If time cannot change, which is trivially
shown to be true (changing time is an oxymoron because it is circular), then
all the so-called time-travel conjectures by famous physicists like Kip
Thorne, Stephen Hawking, David Deutsch, and many others, are pure
crackpottery.

