From: [j h k 6] at [namaste.cc.columbia.edu] (John H Kim)
Newsgroups: rec.games.frp.advocacy
Subject: Re: Realistic FTL?
Date: 19 Oct 93 20:39:11 GMT

	Aaah, I can't stand it anymore.  

	Alright, my apologies to all those who don't care about Relativity - 
you are completely right.  For SF games played by any normal people, the 
best solution is to throw out the Relativistic view of the universe.  People 
don't understand it anyhow, and it just causes problems.  An explanation like 
my 'sub-space currents' simulates many relativistic effects.  Further, it is 
much closer to people's intuitive understanding, and allows for FTL without 
causality worries. 

--------------------

	Now - as far as various people's explanations of why there isn't a 
problem... well, they're wrong.  

	Relativistic time dilation does *not* mean that time is flowing at 
different rates at different places.  It also means more than just the 
slowing down of people's time as they approach c.  Time 'dilation' can and 
does produce a reordering of events. 

As a quick paradox example: 

	An observer on Earth sees a box disappear on Earth, and microseconds 
later (i.e. before a lightspeed signal could travel there) a box appears on 
the Moon.  The Earth observer watches on a telescope, and then subtracts off 
the lightspeed delay to get the exact time it appeared. 

	Now a spaceship zooming past Earth towards the Moon views these same 
events.  It is traveling at 0.9c, so there is considerable dilation effects 
between its view of things and the Earth's.  It watches these two events by 
telescope and subtracts off the lightspeed delay.  It finds that the 2nd box 
appeared on the Moon *first*, then perhaps a second later, the box disappeared 
on Earth.  

	Now, if there were FTL teleportation, this would be an instant 
violation of causality.  The same box teleports from the Earth to the Moon. 
However, to the spaceship it appears on the Moon *first*.  If the spaceship 
can sense that appearance by an FTL messenger, it can stop the teleportation 
from occuring on Earth before the box disappears.  Instant time paradox. 

	However, if there *is* a lightspeed limit, then this is *not* a 
violation of causality.  The appearance of the box on the Moon *cannot* 
be caused by the disappearance of the box on Earth, because it takes light 
at least a second to travel to the Moon.  Hence - they are different boxes.  
If the spaceship stops the Earth box from disappearing, there is no 
paradox. 

	The basis of this is in the formula for translation between two 
frames.  Where the new (primed/apostrophied) frame is moving at velocity 
v along the x-axis of the old frame: 

x' = (gamma)*x - v*(gamma)*t
y' = y
z' = z
t' = (gamma)*t - (v/c^2)*(gamma)*x
                 ^^^^^^^^^^^^^^^^^

	Note this last term, which means that *where* something is in the 
old frame makes a difference in *when* it is seen in the new. 

------------------

	If people have any questions, write to me by email, as this doesn't 
have anything to do with RPG's as far as I can tell.  
---------------------------------------------------------------------------
John Kim                    | Less well known last words:
[j h k 6] at [cunixb.cc.columbia.edu] |     "I fireball the fools who dare to hijack 
Columbia University         |     the _Hindenburg_."