Maxwell’s equations describe light as a wave so in the nineteenth century a superfine ether was assumed to propagate it in space. But if the earth orbiting the sun gave the seasons and its spin gave night and day, the ether wind couldn’t always be stationary (Figure 5.1). The speed of light should vary: light going against the wind should go slower and light going with the wind should go faster. But in 1887, Michelson and Morley found to everyone’s surprise that the speed of light was the same in every direction. There could be no ether wind! This was deeply counter intuitive – how could the movement of the earth not affect the movement of light?
In 1904 Lorentz showed that the equations of light stayed the same if space and time changed as objects moved. In 1905 Poincare deduced the relativity principle, that the laws of physics were the same in every reference frame, so a ball thrown up in a moving car acts the same as in a stationary car. In our world, constant speed observers get the same laws of physics, so throwing a ball, swinging a pendulum or shining a flashlight is the same on a constantly moving platform as on earth.
This is fortunate, as the earth is a planetary platform, carrying us through the cosmos. Its spin whirls us around at about 1000mph, it carries us around the sun at about 66,000mph and we go around the galaxy at an amazing 483,000mph. Some estimate that we move relative to the cosmic background radiation at about 1,300,000mph, yet science works on earth as it does in the rest of the universe. We live on a moving planet, so how is our reality bubble maintained?