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From: swift@reed.UUCP (Theodore Swift)
Newsgroups: net.space
Subject: Re: Speed of Light
Message-ID: <1535@reed.UUCP>
Date: Wed, 15-May-85 04:49:19 EDT
Article-I.D.: reed.1535
Posted: Wed May 15 04:49:19 1985
Date-Received: Fri, 17-May-85 00:05:48 EDT
References: <52@uw-june>
Reply-To: swift@reed.UUCP (PUT YOUR NAME HERE)
Organization: Reed College, Portland, Oregon
Lines: 33

In article <52@uw-june> dtuttle@uw-june (David C. Tuttle) writes:
>So, any ship approaching 1.0c can still be passed by light at 1.0c, thus
>the ship can never bridge that gap and travel at lightspeed...
>
>True physicists are now free to punch holes in this layman's arguments.

Rather than punch holes in it, maybe we can do some tailoring to a suit
with potential, but doesn't quite fit yet.
  The reason anything with mass can't go the speed of light (e.g.,
spaceships) has to do with the not-to-easy-to-grasp idea that as your
velocity approaches v=c, your _relativistic_ mass increases according to
Mmotion=Mrest/sqrt(1-(v*v)/(c*c)).  The mess in the denominator is called
the "gamma function" (dunno why).  If you consider the case where v is
approaching c (from below!! we don't wanna mess with the case v>c,though
one of the seniors did his thesis on just that idea) you should be able
to convince yourself that the sqrt(1-(v*v)/(c*c)) term goes to zero, so
the relativistic mass, Mmotion, goes to infinity.  To get something going
fast (or faster), you need to accelerate it.  You apply a force to the 
mass to accelerate it. (Newton said it best: F=ma).  Now, near c, your
relativistic mass gets to be huge, so the amount of force necessary to
get you going any faster (closer to c) also gets huge.  You just can't 
carry enough fuel to generate "huge enough" forces.
  The gamma function also works on time.  This is the basic idea behind
the "twin paradox" (available in any good intro physics text) where the
twin in a spaceship going at some relativistic speed ages "slower" than
his sibling on the ground (or at rest- he can be suffocating in space for
all we care, as long as his Timex keeps on ticking).  The neet idea
this brings up is that interstellar colonists won't have to go through
*as many* generations before planetfall because, if they get truckin',
they will age "slower" relative to the Infinite Cosmos (sorry, Carl...).
One problem: you gotta slow down, to, unless you just want to leave
E. coli on your target planet.
Enough mister science for now.  I'm going to sleep.