The Young in Space

The great spaceship shuddered briefly as it went into hyperdrive and headed for the Whirlpool Galaxy. Captain Dart watched the hand of the c-meter. It was close to the speed of light, and, getting closer and closer. He felt no change, of course, but he knew that his personal time was already running slow. Each tick of the clock, each heartbeat took months or years of earth time. How old were his friends on earth? he wondered. How long had they been dead?

Such science fiction is not based wholly on imagination. If Captain Dart gets to the Whirlpool Galaxy while he is still young enough to make a safe blast-down on some hospitable planet, he will thank, in part, Albert Einstein and the theory of relativity.

Excessive flight-time has worried spacemen ever since Jules Verne's "voyage" to the moon in a habitable projectile (see cut). Today's rocket speeds are good for trips in the solar system, but for interstellar voyages they are hopelessly slow. Conservative space enthusiasts accept the speed of light as the absolute speed limit in the material universe, and they know that even at this ultimate speed a spaceship can reach only nearby stars within a human generation. This seems to put a limit on man's interstellar mobility. But some optimistic scientists see hope in "time dilation." If a spaceship cruising toward a foreign star approaches the speed of light, its time, by relativity, will slow down. Its clocks will run slow by earth time, and the chemical processes that make its crew grow old will run slowly too. So when the ship reaches its destination thousands of light years away from the earth, the men on board will be almost as young as when they left home. If they could return to the earth, where time has been elapsing at its customary rate, they would notice certain changes. All their friends would be dead of old age, and perhaps the nation that financed their trip would have been forgotten.

Some scientists have never admitted that relativistic time dilation can give any kind of immortality. But in last week's Nature, Dr. Frank S. Crawford Jr. of the University of California (Berkeley) offered theoretical proof that high speed can postpone at least one kind of death.

Methuselah of Space. Instead of sending a human subject into space at close to the speed of light and comparing him physically on his return with stay-at-home contemporaries, Dr. Crawford uses mu mesons. When these subatomic particles are at rest in relation to the earth, they disintegrate in an average earth time of less than two-millionths of a second. But when they are created by cosmic rays hitting atomic nuclei high in the atmosphere, they seem to have comparative immortality. Many of them reach the earth's surface more than ten miles below, although their short "rest lives" would permit them, even moving at the speed of light itself, to travel about one-third of a mile. The reason they travel so far is that their speed, given them by the cosmic rays, makes their time slow down. They live, by earth time, 15 to 20 times longer than if they were at rest. By the same figuring, a man moving at meson speed might live 1,400 years.

Some critics of time dilation claim that a spaceship's slowing down as it nears its destination will have a quick-aging effect on the crew, canceling the years gained by high-speed travel. Not so, says Crawford. He cites a set of experiments in which some mu mesons were brought to rest at an altitude of 11,500 ft. and others at Chicago (600 ft.). Their life expectancies were measured and compared. No evidence was found that their slowing down caused rapid aging.

Death on Return. Dr. Crawford, however, does not go all the way with the space-fiction writers. He thinks that time dilation can, theoretically, keep a man young while he speeds through space and permit him to land, still young, on a distant star. But according to Crawford, the man who has ventured deep into space can never return to earth before his life runs out. To keep the age advantage gained during the fast outward trip, he must make the homebound trip at a comparative snail's pace. His clock will tick on earth time, and he will grow old on earth time. The voyage across light-years of space will take thousands of earth years, and death will overtake him long before he sights the solar system.

This file is automatically generated by a robot program, so reader's discretion is required.