I see, so what happens to the twins then if one is accelerated? Why is this so much different? Please forgive all the hand holding I need, I am not a physics major, I'm actually a communication major....just really interested in physics; my physics knowledge is just starting to accumulate so I find it very difficult to follow some of the concepts in the link you provided. Actually I don't quite understand how to read the graphs. I wish I had the time to take more physics courses!
* From: John Denker <jsd@av8n.com>
* Date: Sun, 04 May 2008 13:17:55 -0700
RE:
*) Let's assume _uniform_ motion. No acceleration. That is,
let's not get this mixed up with the infamous twins, one of
whom is _accelerated_. http://www.av8n.com/physics/twins.htm
*) 100 years of proper time is 100 years of proper time. The
modern (post-1908) viewpoint is to think of each clock's
proper time as "the" time for that clock.
*) Stop trying to explain what happens to the clocks. Nothing
happens to the clocks.
*) There is no such thing as "the" stationary observer. Each
guy is stationary in his own frame.
The situation is completely symmetric. Each guy observes
that the other guy is moving. That is, relative to the blue
guy the green guy is moving and vice versa. This symmetry
is easy to see if you draw the spacetime diagram. It is
also easy to see in the math: The space/time rotation matrix
[ cosh sinh ]
[ ]
[ sinh cosh ]
has a rather obvious symmetry
*) I won't say anybody's clock "is" slow. The /projection/ of
each guys clock onto the other guy's frame is slow. That's a
property of the projection, not a property of the clocks.
By way of analogy, consider a flagpole whose length (proper
length!) does not change. However the length of the shadow
of the flagpole does change during the course of the day.
I don't have a problem with that. The shadow is a perfectly
real thing, and sometimes has direct physical significance.
But don't think that the shadow "is" the flagpole.
*) The Subject: line needs to be changed, but I'll let it slide
for now. There's nothing special about the behavior of light.
This has to do with the geometry and trigonometry of spacetime,
which affects all reference frames equally, whether it involves
the presence of light, and/or something else, or nothing at all.