A hundred years ago, one of the most fundamental questions in physical science was: How fast is the Earth moving? Many experiments had been performed to measure the speed of the Earth through space as it orbits the sun, and as the solar system orbits the galaxy. The most famous was conducted in 1887 by Albert Michelson and Edward Morley using an optical interferometer. The result they obtained was... zero. Today, scientists regard the question of the Earth's speed through space as meaningless and misconceived, although many non-scientists still refer to the concept.
Why has the question disappeared? Einstein's theory of relativity, published in 1905, denied any absolute frame of rest in the universe; speed is meaningful only relative to other bodies or physical systems. Ironically, some decades later, it was discovered there is a special frame of reference in the universe defined by the cosmic microwave background radiation, the fading afterglow of the big bang. The Earth sweeps through this radiation at roughly 600 km per second (over a million miles per hour) in the direction of the constellation Leo. This is the closest that modern astronomy gets to the notion of an absolute cosmic velocity.
PAUL DAVIES is an internationally acclaimed physicist, writer and broadcaster, now based in South Australia. Professor Davies is the author of some twenty books, including Other Worlds, God and the New Physics, The Edge of Infinity, The Mind of God, The Cosmic Blueprint, Are We Alone? and About Time. He is the recipient of a Glaxo Science Writers' Fellowship, an Advance Australia Award and a Eureka prize for his contributions to Australian science, and in 1995 he won the prestigious Templeton Prize for his work on the deeper meaning of science.