Light may vary in speed but we are unable to detect that because both our perceptual apparatus and our brain function via electromagnetic transmission.
My fiction novel Time is Gold will be published soon. Maxi is a marathon runner who applies relativity theory in her brain and dilates time.
Relativity causes movement in a faster time frame to dilate time, either for an astronaut or for a stimulus response signal in human nervous system. Time dilation is explained below.
Einstein did a thought experiment about a spaceship. An astronaut inside it flashes a pulse of light perpendicularly across the spacecraft, setting off a timer and reflecting back from a mirror to the timer again. The travel time across the width is T seconds read from the timer.’
If the spaceship moves forward at the speed of light, would the travel time T across the spaceship and back be the same as when it was stationary?’
If we could look inside through a porthole using a telescope from Earth, we would see the path of the light pulse illuminating dust particles in the air along a diagonal path to the mirror in its new position, being reflected off the mirror and coming back along another diagonal, completing a dogleg.
Can the light pulse still go across in T? It has three conditions to obey. 1. The diagonal path is further than the path perpendicularly across; 2. It must arrive by the same time T; and 3. It cannot go faster than the speed of light.
It can’t, because to go further along the diagonal in the same time, it would have to go faster. But if it was already at the speed of light and couldn’t go faster. Nor could it arrive after the time the astronaut would observe.
Therefore it would be impossible for the pulse to be seen at the same time. Einstein supposed time would dilate or stretch. If each second lasted longer, it would make sense. We are used to a pendulum beating out constant aliquots of time but at high speeds it would have to beat more slowly and because each second would be longer, the longer distance could be travelled in fewer seconds.
Next in this series it is shown how time dilation for a person in a much faster time frame would cause a higher speed of travel.
My fiction novel Time is Gold, to be published shortly, tells how an athlete exploits metaphysics and wins. http://www.martinknox.wordpress.com