From: news@sifon.cc.mcgill.ca
Subject: Re: Not the Technical Manual
Organization: McGill University
Date: Wed, 18 Nov 1992 15:12:49 GMT

In article <8758@dirac.physics.purdue.edu> hinson@bohr.physics.purdue.edu (Jason W. Hinson) writes:
>chris@keris.demon.co.uk (Chris Croughton) writes:
>>In article <8738@dirac.physics.purdue.edu>
>>           hinson@bohr.physics.purdue.edu writes:
>>
>>>No one seems to realize the impact that changing one single thing in
>>>time can have on future events.  Star Trek always comes out with some
>>>way of handling it, such as Samual leaving his watch where he knew it
>>>would be found.  But he HAD to do that, so he didn't have free will.
>>>But time travel is another discussion all together.
>>
>>It depends on your model of time.  One theory says that small changes
>>will only have local effects, so in a few hundred years time it won't
>>matter.
>
>This idea has never seemed realistic in the least to me.  Someone once
>pointed out that all you have to do is run around a town on any given
>night and knock on doors and run.  By doing this, you are going to
>"interrupt" some people, and since time of conception can change the
>type of child born, you probably have changed who will be around to
>effect furure events.  Just think of when you personally tell someone
>something that has a small effect on their lives.  That effect may be
>small, but it is there, and it effects other things. ANYWAY
>
Jay's right about this.  Someone cited Strange Attractors from Chaos
theory to argue that physics wouldn't be changed but what Jay said above
is actually closer to what Chaos theory actually tells us.  True, if you
killed Hitler before the Second World War even began, then there *might*
still be a Second World War but then someone else would have to take
Hitler's place and he would inevitably make different decisions.  This
gets back to the idea of free will.
>>
>>>As far as violating causality through FTL travel, I beleive I have a good
>>>argument as to why it is not done in ST technology.  If it were, we would
>>>see its effects all the time!                                         You
You get a distress call from a planet.  You
>>>are running out of time to get there.  All you have to do is get in the
>>>right frame of reference out of warp, then enter warp, and you can get there
>>>any amount of time after the destress signal was sent or even before it
>>>was sent.  We do NOT see this at all.  This is why I don't think the idea
>>>you mentioned about keeping the same F.O.R. you have before you enter warp
>>>is correct.
>>
>>This I don't see.  Planet (A) sends a call to the Enterprise (E).  This
>>is not at infinite speed, so it takes a time Tsig = Dae / Vsig.  E
>>receives the signal, and travels to the planet.  This takes a time
>>Te = Dae / Ve.  This time is still positive.  Because of relativistic
>>effects E and A may disagree on exactly how *large* this time is in
>>subjective time, but both will agree that it is positive.
>>
>>The only time that Te could be negative is if you try to force the time
>>dilation equations of Special Relativity to handle velocities greater
>>than c.  That gives complex values, rather than negative, anyway, which
>>I don't think means reversing time, but (if it has any meaning at all)
>>moving somehow 'sideways' in time...
>>
>>Surely special relativity wouldn't apply anyway, because E is
>>accelerating wrt A?
>>
>Funny you should ask.  I just gave this explantion to a net-friend.  It
>is important that you understand a Lorentz transforms. NOTE: two different
>frames of reference CAN dissagree as to whether an event is in the future
>or the past.
>
>SO, here is an example of how a causality problem can occure:
>
>You are traveling at the same speed as another ship that is 2 light years
>away from you.  You receive their message at x = t = 0.  NOW, lets say
>they sent the message at x = -2 lyrs and t = -1.31893E-3 yrs.  That's how
>long it would take the signal to get to you at warp 9 (I used it just
>because it is easy to calculate).  By setting the ship at a negative
>x, I have just defined the direction of the one space coordinate that
>I will use.
>
>NOW, using Lorentz transforms, I came up with the following fact: If you
>travel away from the ship at a velocity of
>v = 1.45220878778E-3 c then (keeping all numbers in light years and
>years and expressing c as 1 lyr/year) you get:
>
>ct' = gamma(ct - beta x)
>    = (1.00000105446) [-1.31893E-3 yrs (1 lyr/year) - beta*(-2 lyrs)]
>    = 1.68649E-3 years = 13.8 hrs IN THE FUTURE
>
>This assumes that you can get to that speed (about 435663m/s) very
>quickly so that you are still close to x = 0 when you get to that
>velocity. If not, then you have to add on a little correction.
>
>So, in that FOR, the event has not happened yet.  It is 13.8 hrs in
>the future.  Now, if you can then inter warp while KEEPING this frame
>of reference, you can go to warp 9 and get there in 11.6 hrs.  This
>gives you over 2 hours to help them BEFORE they send you the signal.

(rest of the explanation omitted)

He's right.

For that matter, according to my scheme, if the Enterprise were to
enter warp, proceed at warp 9, drop out of warp, apply a boost of
1.45220878778E-3 c, re-enter warp, turn around and proceed at warp 9
then they would arrive at their starting point 2.2 hours before they
left.  I hadn't realized this, mainly because I didn't consider the
idea of turning around while in warp, something that was demonstrated
in TOS: "Let That be Your Last Battlefield" in which they were "going
nowhere mighty bloody fast".  I sincerely appreciate the time Jay put
into thinking up this counter-example.

Oh well, at least it wouldn't happen "all the time". :)

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Martin Phipps (aka Cliche Lad)  ! LOULA@hep.physics.mcgill.ca or simply
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