Abstract

Imagine an ordinary garden fence. Well, not exactly ordinary. It should be infinitly long, or, if this is too much for you: arbitrarily long. The space between the posts, say 10 inches, should be enough to let a ball come through, its diameter being slightly less than the gap between the posts. Alongside the fence, infinitely near, are the rails of a special train, the "Einstein train", its peculiarity being the ability to achieve very high velocities - velocities near the limiting veolocity of light.  The Einstein train with a ball slightly smaller than the gaps between the posts. We enter Einstein?s train and accelerate, until our speed approaches that of light. Now we have two ways of perceiving the same fact. If we peer through the gaps in the garden fence, things look like this, according to Einsteins length-contraction:  The Einstein train, approaching the velocity of light, as seen from the fence. The ball can still be tossed through the gaps. Now take another standpoint. We hop on the train and look at the garden-fence. According to Einstein?s length-contraction, things now look like this: