I think I read that you have to either do extremly complicated equations or measure the speed from a nonmoving frame of reference, to tell the actual speeds(all of which are less than light).
Trouble is there is no such thing as a non-moving frame of reference.
I remember a simple example that my college physics proffessor showed us once to demonstrate relativity and why time is the variable rather than light speed. You have to have a pretty good imagination for this.
There is an observer on an asteroid who watches a spaceship fly past at high speed.
On board the spaceship is another observer who carries out an experiment to measure the speed of light. he fires a light beam from one side of the ship to the other, where it hits a mirror and returns to a detector at the source. He knows the distance travelled and he measures the time taken so he can easily calculate the velocity. Distance = twice the width of the ship. Time = t. Go figure.
The observer on the asteroid is able to watch the beam of light that traverses the spaceship and makes his own measurements of it. To him the light beam doesn't simply cross the ship and back in a straight line, It travels diagonally as the spaceship is moving. Let's say the ship is moving at the correct speed for the light beam to be moving at a 45 degree angle to the perpendicular.
From the asteroid observer's frame of reference, the light beam travels a much greater distance than it does for the observer on the spaceship. he measures that distance as 2 * the square root of (double) the square of the width of the spaceship using simple trigonometry.
He calculates the speed of light from his time and distance measurements.
According to Einstein, both observers will measure the speed of light to be exactly the same.
We know that the light beam must actually be moving in the way that the observer on the asteroid sees it since the ship is in motion. It is logical that the light beam must be moving with the direction of the spaceship's travel and not just side to side since it takes a finite time to complete its trip.
Therefore, in order for the observer on the spaceship to measure the speed of light to be the same universal constant, his time must be moving slower than that of the observer on the asteroid. (relatively)
Everybody follow this still?
I will leave it at this point before carrying on. More later.
:D PY :D