The Speed of Light

I recently saw a PBS documentary on Albert Einstein in which much of the history of his “relativity” postulating was revealed. In particular, Einstein had been perplexed by the notion, previously proven by Maxwell, that light travels at 186,000 miles per second (about 670 million miles per hour) independent of the speed of its source or that of the observer. Einstein would imagine himself riding on a beam of light and shining another light which would then also travel off at the speed of light – an obvious logical conundrum. Einstein solved this problem when he realized that, as objects speed up, time slows down. Thus, as he sat on a beam of light, an eternity at the original light source would be zero time to Einstein. (This is the basis of much science fiction that has austronauts, after traveling through space at a very fast rate for a few of their years, return to earth to meet their great-great-great grandchildren. Also, please note that Einstein's postulate has indeed been proven by comparing atomic clocks sent into space and returned to be compared with their calabration twins kept here on earth.)

Now this notion of relative time creates its own conundrums. We are traveling at various speeds through the cosmos. At the equator, we are rotating around the earth’s circumfrence (about 28,000 miles) every 24 hours … or at about 1,150 miles per hour. We on Earth are also traveling in our orbit around the sun ever year, which works out to be about 67,000 miles per hour. The sun is also traveling around the black hole at the galatic center of the Milky Way at about 250 kilometers per second (559,000 miles per hour). And the Milky Way itself is traveling on its own track throgh the fabric of the cosmos at a speed combining both absolute displacements from other galaxies and the speed it inherits from the big bang expansion (being relative to its distance from the edge of the universe). I have been unable to quantify this speed … but it is certainly in the millions of miles per hour. (The edge of the universe itself is thought to be expanding at the speed of light.) The result of all this is that “time” through the universe progresses relative to other locations at rates different from one another by factors from nanoseconds up to eons. (However, these discrepencies can probably never be fully reconciled because time appears to be consistant at individual observation points.) To me, this suggests that the notion of multiple parallel universes may not be that far-fetched after all ... they are here with us in ours.

(Note: “speed of light” is an unfortunate term because all electromagnetic radiations (X-rays, gamma rays, microwaves, etc.) travel at this same rate in a vacuum … as well as does the edge of our expanding universe. Thus 186,000 miles per second might be better named the “limit of speed”.)