No no no, I understand how time travel screws
around with causality. If I go back in time
and give Lee Harvey Oswald a wedgie, thus saving
JFK (I'm assuming no other shooters), then events
happen in 1963 (JFK celebrates Thanksgiving) due
to an action taken in 2008 (me getting on my time
machine).
Then of course there's the whole question of if I
know JFK's life was saved why do I bother going
back? According to the history books, he doesn't
need any help from me.
Even if I just go back an hour and stand still for
a minute and then come back, you still have the
situation that some O2 was converted to CO2
*back then* because of something I did an hour
later.
Corkscrew causality.
But it seems that FTL *without* time travel
wouldn't have causality problems. Perhaps FTL
inevitably involves time travel, but then again,
there might be a loophole.
> But it seems that FTL *without* time travel
> wouldn't have causality problems. Perhaps FTL
> inevitably involves time travel, but then again,
> there might be a loophole.
suggests we are living in a Relativistic world. Global positioning
satellites must allow for Relativistic speed and gravity to account for
their position, which would be miscalculated under Newtonian laws.
In both models, Time Travel would violate the notion that
matter-and-energy can be neither created nor destroyed. (This axiom is
the cornerstone for most of our understanding of physics.) Traveling
backward would cause the addition of your mass to be created in the past
universe. Skipping forward would subtract your mass, leaving an
unexplained destruction of your matter-and-energy, then recreate your
matter-and-energy upon arrival. A "Rip van Winkle" approach to moving
forward is possible, since we all ride forward in time anyhow. But
unless you were plucked cleanly from your current dimension, any
transition backward in time would result in the forward and backward
'you' trying to occupy nearly the same space at your transition event.
In Relativity, *Simultaneity* of an event differs according to one's
speed approaching or receding from that event. An FTL signal could tell
you what to expect to happen at a planet you are yet approaching,
introducing paradox.
- Twisty
Yeah, the mass-creation thing alone probably makes
time travel impossible. First occurred to me when
I was reading a "juvenile" where the character had
a hand-held time machine he called "the Egg." He
decided he wanted several, so he set the Egg in
his closet and waited an hour. Then he opened the
closet, picked up the Egg, and traveled back
fifty-nine minutes. He opened the closet, and
there was the Egg. He set own Egg next to it and
waited. Then he picked up both Eggs, went back
fifty-eight minutes, opened the closet and set his
two Eggs next to the two already there. Repeat as
needed, and you could have thousands of Eggs.
would have increased in mass by the value of many
Eggs in a single hour.
So I get it with time travel. I just don't get it
with non-time-travel FTL. I'm not arguing that
it's not true. A lot of really smart people with
tons of education in exactly this sort of thing
seem to think it's that way, and they would know
better than I would. So I'm not saying it's wrong,
I'm just saying I don't quite get it. Maybe I can't.