The expansion of the universe is much more of a gentle tug that only becomes dramatic over large distances. His observations and simple reasoning still set the tone for almost all of modern cosmology, or the study of the universe. You observe this effect whenever anything passes by you at reasonably high speed. The effect is caused by the sound waves of a moving object getting stretched out behind it as it passes by. Stretched out sounds waves mean a lower pitch, which is why a car's radio sounds off-key when it drives past you.
Light is a wave too, and the same thing happens when objects move by one another.
In the case of light, it's not a pitch that changes, but a color. The more stretched out the light is, the more red it looks. Calif. Its mirror was 100 inches across - by far the largest telescope in the world at that time. A group of astronomers led by a man named Hubble began to photograph the mysterious giant star clusters known as galaxies. It was far too red.