The constant speed of light (c) on which spacetime theory is based
     In the late 1800's, when an ether medium was in vogue, experiments by Michelson and others appeared to rule out the possibility of the medium and show that the speed of light is constant relative to all bodies such as Earth or a spaceship coasting with constant velocity through the cosmos. It is still generally believed and taught that a photon from Star A and a photon from Star B (below) arrive with the same speed relative to the spaceship, even when the ship is moving at half the speed of light away from A and toward B.

     You may think it's impossible for photons from A and photons from B to have the same speed relative to the ship traveling away from A and toward B, but this is what experimental results indicate when interpreted in the conventional way and without understanding the consequences of the medium. Most physicists do not question this constant light speed because it is based on experimental evidence, and it has been learned and taught for over a century.

     The constant speed of light, customarily designated by the letter c, is a cornerstone of modern physics theory in spite of the fact that modern physics cannot explain how it is possible. It is the assumption underlying relativity theory (i.e. spacetime theory) that results in the theory's strange predictions (e.g. slowing of clocks moving relative to the observer) -- predictions of strange phenomena that are in agreement with experimental results and therefore suggest that relativity theory is correct. As shown in the Glossary, Einstein says the following about c in his book, Relativity: The Special and the General Theory.

There is hardly a simpler law in physics than that according to which light is propagated in empty space. Every child at school knows ... that this propagation takes place in straight lines with a velocity c=300,000 km./sec. ... In short, let us assume that the simple law of the constancy of the velocity of light c (in vacuum) is justifiably believed by the child at school. Who would imagine that this simple law has plunged the conscientiously thoughtful physicist into the greatest intellectual difficulties?

      This strange law leads to relativity theory's strange conclusions. For example, it leads to the conclusion that an observer on the spaceship and an observer at Star A or Star B above can not agree on the distance between the stars or the length of the ship, and that distances are therefore observer-dependent. The law leads to predictions of other strange phenomena that also agree with experimental evidence. The following pages show that the quantum medium view predicts the same experimental evidence and that it reveals logical physical causes for phenomena such as c that seem strange or inexplicable until their causes are understood.