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The two axioms of Einstein's theory of Special Relativity. 1. The laws 
of physics are independent in all inertial (non accelerating) reference 
frames. That is if you are traveling in a car on a straight road at 
constant speed you can drink you soda without it going all over the 
place just the same as you can stopped at a stop light. You can play 
ping pong on a moving train if it's not speeding up, slowing down or 
going around a curve just the same as you can in your rec room.

2. The speed of light in a vacuum is a universal constant - independent 
of motion of the light source.

There is a pretty good lay discussion at 
http://en.wikipedia.org/wiki/Special_relativity.

Those sound simple but - they carry a wallop. First there are no 
preferred frame from which to make measurements. This results if I am 
"at rest" and measure your atomic clock that is moving - I will observe 
your clock to be moving slower than the same atomic clock in at rest in 
my references. However, you are at rest in your reference frame and you 
will measure my clock to be slower than yours.

These postulates also have the effect of tying space to time (since 
distance is measured by the time it takes electromagnetic energy to 
travel) one gets observes both a time dilation and spatial dilation. 
Relativity knocked time off it's pedestal it had enjoyed till 1905 as 
being "absolute." It is not - it is relative to the observer.

The speed of the clocks don't really change but how they are observed 
changes depending on the reference frame in which they are measured 
(this is a result of the second axiom).

This is the most tested theory in physics and experimental results 
agreement with prediction has always been within the measurement 
limitations of the instrumentation.

Why do you care and how is it endurance related? If you ride with a GPS 
it impacts you. Because the velocity of the GPS satellite is very large 
it relativistic effects of have to be considered. There are actually two 
relativistic effects - one is the special relativistic effect and the 
general relativistic effect (from gravity). This means that the clocks 
on board the space crafts have to be adjusted by 44 thousand 
nanoseconds/second and the receivers have to have software to compensate 
for the dilation effects in order for the system to work. This is so 
time transfer will be accurate and you and the satellite are on the same 
time. They also have to adjust for the Sagnac effect because both the 
earth and satellites are in a rotating frame 
http://en.wikipedia.org/wiki/Sagnac_effect. Another practical use of the 
Sagnac effect is laser gyroscopes which are extremely accurate.

For most things on the earth the relativistic effects are present but 
are negligible - when a satellite is involved that is no longer true. As 
we are tying to do more and more precise and accurate remote sensing 
from space - we are finding that we have to be more and more careful in 
understanding both the relativistic and quantum effects and compensate 
for them in the design and processing of the sensor data.

For example some of the original imaging radar images produced by the 
old SR71 Blackbird imaging radar payload were all fuzzy because of the 
impact of time/distance dilation and in order to focus the images - 
relativistic effects had to be considered in the processing. So even at 
that Mac 3, for some high performance sensor applications, relativistic 
effects had to be factored in.

More than you ever wanted to know.

Truman

Sisu West Ranch wrote:

> Perhaps we should also consider the possibility that the Fitzgerald* 
> contraction can affect saddle fit on an Arabian horse.
>
> Ed
>
> *There was a young man named Fisk
> Whose fencing was exceedingly brisk
> When he went into action
> The Fitsgerald contraction
> Diminished his sword to a disk
> ---Anonymous
>
> Objects going at speeds very close to the speed of light appear to an 
> outside observer to be shorter than they were at rest.
>
> (Actually, if I remember correctly, from the point of view an observer 
> on the horse neither the horse or saddle would appear to change in 
> length. This is puzzling to me since the observer on the horse would 
> know that it was him and the horse that had changed speeds and thus 
> were going near the speed of light. I'm sure that Truman can give a 
> better explanation. He actually uses this stuff, I was mostly involved 
> in "Carpet Science" not rocket science.)
>
> Ed
> Ed & Wendy Hauser
> 2994 Mittower Road
> Victor, MT 59875
>
> (406) 642-9640
>
> ranch(at)sisuwest(dot)us
>
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--

“Ethical axioms are found and tested not very differently from the 
axioms of science. Truth is what stands the test of experience.” Albert 
Einstein


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