Einstein analyzed what is necessary to maintain our reality bubble as follows. He imagined a moving train where a floor light reflects from a mirror up on the ceiling. A train passenger sees the light go straight up and down but a platform observer sees it travel a longer path in the same time (Figure 5.2). If time and space are the same for both, they get a different speed of light and different physics. Einstein deduced that space had to shrink and time dilate to keep the speed of light constant. Lorentz saw his transformations as mathematical curiosities but to Einstein they were what made Poincare’s relativity work. Einstein saw that for the universe to be as Poincare described, space and time had to change as Lorentz described. Space and time had to change to make physics invariant or torches might not always shine and mirrors might not always reflect!
The implications of this are strange indeed. Imagine a rocket flying past a space station in orbit (Figure 5.3). It seems impossible that people on the rocket and on the space station both get the same speed of light, but they do! If they didn’t, our physics wouldn’t work on Mars.
But who is really moving – is the rocket going past the space station or is the orbiting space station passing the rocket? It turns out that it doesn’t matter. If the rocket moves, its space and time contract and dilate, or if the space station moves the same applies. Regardless of how the rocket and station move relative to each other, distance and time change just enough to keep the speed of light the same for both. For a particle model, this extraordinary finding makes no sense at all.
Experiments have verified that time and space change as matter moves. It seems weird that time and space change with speed but as Einstein said, this is why the universe isn’t weird. That the speed of light is constant for all movement is why we appear to live in a “normal” universe.