Broca's Brain - Carl Sagan [120]
The original motivation for traveling fast must have been, as the whiting’s plaint reminds us, to escape from enemies and predators, or else to seek enemies and prey. A few thousand years ago a remarkable discovery was made: the horse can be domesticated and ridden. The idea is a very peculiar one, the horse not having been evolved for humans to ride. If looked at objectively, it is only a little less silly than, say, an octopus riding a grouper. But it worked and—especially after the invention of the wheel and the chariot—horseback or horse-drawn vehicles represented for millennia the most advanced transportation technology available to the human species. One can travel as much as 10 or perhaps even 20 miles an hour with horse technology.
We have emerged from horse technology only very recently—as, for example, our use of the term “horsepower” to rate automobile engines clearly shows. An engine rated at 375 horsepower has very roughly the pulling capacity of 375 horses. A team of 375 horses would make a very interesting sight. Arrayed in ranks of five horses each, the team would extend for about two-tenths of a mile in length and would be astonishingly unwieldy. On many roads the front rank of horse would be out of sight of the driver. And, of course, 375 horses do not travel 375 times as fast as one horse. Even with enormous teams of horses the speed of transportation was only ten or so times faster than when we could depend upon only our legs.
Thus the changes of the last century in transportation technology are striking. We humans have relied on legs for millions of years; horses for thousands; the internal-combustion engine for less than a hundred; and rockets for transportation for a few decades. But these products of human inventive genius have enabled us to travel on the land and on the surface of the waters a hundred times faster than we can walk, in the air a thousand times faster, and in space more than ten thousand times faster.
It used to be that the speed of communication was the same as the speed of transportation. There were a few fast communication methods earlier in our history—for example, signal flags or smoke signals or even one or two attempts at arrays of signal towers with mirrors employed to reflect sunlight or moonlight from one to another. News of the recapture of the Fortress of Györ by Hungarian commandos from the Turks was apparently conveyed to the Hapsburg Emperor Rudolf II through such a device: the “moonbeam telegraph,” invented by the English astrologer John Dee, which apparently consisted of ten relay stations placed at intervals of forty kilometers between Györ and Prague. But with only a few exceptions, these methods proved impractical, and communications proceeded no faster than a man or a horse. This is no longer true. Communication by telephone and radio is now at the velocity of light—186,000 miles per second, or about two-thirds of a billion miles per hour. This is not simply the latest advance: it is the last advance. So far as we know, from Einstein’s Special Theory of Relativity, the universe is constructed in such a way (at least around here) that no material object and no information can be transmitted faster than the velocity of light. This is not an engineering barrier like the so-called sound barrier, but a fundamental cosmic speed limit built deeply into the fabric of nature. Still, two-thirds of a billion miles per hour is fast enough for most practical purposes.
What is remarkable is that in communications