Because it makes for a good story.

The mechanics of time travel are not known and everything around it is
purely speculation.

In the movie Back to the Future II, it was
explained how going back in time would
alter the future and, as such, you would
end up in a paralel time line- one in which
your arrival from the future happens.

Biff from the future would never have
returned to the same future after altering
his past- stealing the Delorian and giving
his younger self a fifty year sports alminac.
But, even if the Doc built a new time machine,
he and Marty wouldn't end up going back to the
altered 1995- future of altered Biff- but
instead would have arrived back to the past
they left at the begining of the second movie.
And the alminac would only have worked for
Biff's yonger self for the first two bets at
the most before that altered reality deviated
from the origional time line making the rest
of the alminac worthless.

In the origional terminator, the idea was that
the AI machines in the future built a time
machine and sent a robot back to kill the
mother (Sara) of the human commander who defeated
the machines. Then the human soldiers destroy
the AI and use the time machine to send a
soldier back to defend the would-be mother
from the robot. So, then the origional
Terminator is actually a sequal- an altered
reality in which these dudes from the future
come back and change the past. The story ends
with the solder getting killed, the robot
getting crushed and the woman winds up
pregnant with the soldiers baby- the soldier
becomeing the commanders father.

What would have happened in the origional
time line? I guess Sara would have met some
other guy who would have been the dad of
the future commander. Then, they would have
lived like normal people until the nukes are
all lauched in 1997. Perhaps they are on a
boat cruse at that time and so everything is
toast when they get back to shore. Then her
husband gets killed by a robot so she takes
her son south into mexico, along with lots of
other displaced americans, where she dies of
cancer and her son becomes the great
commander who defeats the robots and the AI
out of his drive for revenge ...I guess.

My only question then is, why send anyone
or anything back to defend Sara or her son
when the robots only went back to an altered
reality- the first one being uneffected? Also,
since things that go back in time pass into
alternate realities, would they represent a
loss of matter/energy from the origionating
universe while a gain of matter/energy to
the destination universe- the altered reality?

Lawrence Hyde wrote:

In the movie Back to the Future II, it was
explained how going back in time would
alter the future and, as such, you would
end up in a paralel time line- one in which
your arrival from the future happens.

Physical reality does not tolerate contradiction.

[snip]

What would have happened in the origional
time line?

Larry Niven has a lovely story about parallel universes. If you
can spin off arbitary realities at will then it makes no
difference what you do in this one - all actions and their
opposites and every possible variation thereupon occur anyway.
Do what you want, and society disintegrates.

Common observation reveals that betting on hard 8 makes a
difference, and the chance of winning a state lottery is the same
(within an epsilon) whether you buy a ticket or not.

[snip]


--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf

"Lawrence Hyde" wrote in message
om...
snip

If I tell you that everything I say is a lie, would you believe me?

You run into similar question with going back in time, (killing your parents
before you were born, etc)

Lawrence Hyde wrote:

In the movie Back to the Future II, it was
explained how going back in time would
alter the future and, as such, you would
end up in a paralel time line- one in which
your arrival from the future happens.

Biff from the future would never have
returned to the same future after altering
his past- stealing the Delorian and giving
his younger self a fifty year sports alminac.
But, even if the Doc built a new time machine,
he and Marty wouldn't end up going back to the
altered 1995- future of altered Biff- but
instead would have arrived back to the past
they left at the begining of the second movie.
And the alminac would only have worked for
Biff's yonger self for the first two bets at
the most before that altered reality deviated
from the origional time line making the rest
of the alminac worthless.

In the origional terminator, the idea was that
the AI machines in the future built a time
machine and sent a robot back to kill the
mother (Sara) of the human commander who defeated
the machines. Then the human soldiers destroy
the AI and use the time machine to send a
soldier back to defend the would-be mother
from the robot. So, then the origional
Terminator is actually a sequal- an altered
reality in which these dudes from the future
come back and change the past. The story ends
with the solder getting killed, the robot
getting crushed and the woman winds up
pregnant with the soldiers baby- the soldier
becomeing the commanders father.

What would have happened in the origional
time line? I guess Sara would have met some
other guy who would have been the dad of
the future commander. Then, they would have
lived like normal people until the nukes are
all lauched in 1997. Perhaps they are on a
boat cruse at that time and so everything is
toast when they get back to shore. Then her
husband gets killed by a robot so she takes
her son south into mexico, along with lots of
other displaced americans, where she dies of
cancer and her son becomes the great
commander who defeats the robots and the AI
out of his drive for revenge ...I guess.

My only question then is, why send anyone
or anything back to defend Sara or her son
when the robots only went back to an altered
reality- the first one being uneffected? Also,
since things that go back in time pass into
alternate realities, would they represent a
loss of matter/energy from the origionating
universe while a gain of matter/energy to
the destination universe- the altered reality?

Google 'grandfather paradox' and you'll get 31,800 results. No one here
even pretends to know and understand everything about time travel, so
why can't sci-fi movies stay fiction?