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From: dtuttle@uw-june (David C. Tuttle)
Newsgroups: net.space
Subject: re: Speed of Light
Message-ID: <52@uw-june>
Date: Fri, 10-May-85 01:42:30 EDT
Article-I.D.: uw-june.52
Posted: Fri May 10 01:42:30 1985
Date-Received: Sat, 11-May-85 01:41:43 EDT
Organization: U of Washington Computer Science
Lines: 41

Well, there's nothing like a layman that can (try to) explain things to
another layman, so concerning the Speed of Light problem, I'll give it a
shot (trying to remember my sophomore-level physics from 6 years ago):

> \-------/   (Ship #2 going at .9C)  (Laser, at 1.0C)       (Ship #1 at 0.1C)
> |	 |			>--> ------------------------	>-->
> | Earth|----------------------------------------------------	>-->
> |      |  (Laser, going at 1.0C)
> /-------\

> Ship #1 took off first, a LONG time ago, going in the same direction at
> 0.1C (relative to Earth!). 
> Ship #2 now takes off going at .9C (relative to Earth!) and fires a
> SECOND laser in the same direction, said second laser traveling at 1.0C
> (relative to Ship #2, NOT to Earth!!). 
> Hence, BOTH lasers are going at 1.0C, but RELATIVE TO DIFFERENT BASES.
> When both lasers get to Ship #1, won't the laser from Earth have an
> apparent speed of .9C (C minus the speed of Ship #1 (.1C)), and won't
> the laser from Ship #2 have an apparent speed of 1.8C (.9C Ship #2
> velocity plus 1.0C speed of laser minus 0.1C velocity of Ship #1)? 

The problem here is thinking of relativistic speeds as being LINEAR.
In fact, they are NOT (0.9c + 0.9c does NOT equal 1.8c).
Instead, the speed of light is ASYMPTOTIC.  
A ship traveling at 0.9c would view a laser overtaking it at 1.0c as going
by at 1.0c, not 0.1c (although it might be severely blueshifted (?))!

So, when you say the second laser travels at 1.0c relative to Ship #2, but
not to Earth, that is wrong.  It is 1.0c relative to ALL frames of reference.
In fact, "relativity" is a misnomer in that sense, because the speed of 
light comes out as absolute as ever!  The only difference in the lasers will
be that of the Doppler effect (redshift and blueshift).

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.
============================================================================
"No matter where you go, there you are..."		David C. Tuttle
			-- Buckaroo Banzai		Computer Sci. Dept.
							U. of Washington