Time Dilation

Time dilation as stated by Einstein's Special Relativity Theory, is an effect that can be seen when two different observers view the same event from different positions. The theory states that if you set up an experiment on a train using two mirrors and a light source, an observer on the train would time the light beam travelling at the speed of light. An observer on the ground watching the train go passed will observe the light beam travelling at the speed of light, however the motion of the train makes it look like the light has further to travel on the outward part of the journey. So it would to the outside observer look like the light is taking longer to travel from one mirror to the other. However it would seem to travel quicker on the return trip, so wouldn't the observer time the lights round trip in the same time as the on board observer?

There are lots of factors to think about here but in theory x(outward trip)+y(return trip)=c (the speed observed on the train) So it is possible in this example that time dilation may not occur fully just in the timings for the individual runs of the light beam.

In an attempt to prove time dilation the Smithsonian Astrophysical Observatory sent a Scout rocket to a height of 10,000 km in 1976. At this height, a clock should run observably faster than one left on the Earth. The rocket transmitted timing pulses from a maser oscillator which acted as a clock during two hours of free fall from its maximum height. The readings were compared with a similar clock on the ground and the result confirmed the gravitational time dilation relationship to within 0.01%.