Time Travel

Long before time travel was embraced by science, the subject captured the imaginations of shamans, mystics, and science fiction writers. In his novel The Time Machine, H. G. Wells depicted a world where the past, present, and future coexist all at the same time. The distant future was a terrifying realm where murky, subterranean beings cannibalized the people who lived above ground. And returning to the past was as simple as making a [Page 1365]U-turn on the highway of time. For centuries, perhaps thousands of years, time travel to both the past and the future has been a persistent dream.

In 1905 Albert Einstein brought time travel into scientific discussion with his special theory of relativity. In a “thought experiment,” Einstein demonstrated that a clock moving through space will tick more and more slowly the faster it travels, until it stops completely at the speed of light. (A clock could never actually attain the speed of light, however, because its mass would become infinite at that speed.) Ever since Einstein, it has been assumed that because the tick of a mechanical or atomic clock slowed with increasing speed, a way to travel into the future had been discovered. This widely accepted theory of time travel is explained by the so-called twins story.

Imagine that spaceships in the future are capable of traveling near the speed of light. A twin decides to journey to another solar system 15 light years distant while his brother stays home. Because the traveling twin is moving at high speed, his clock slows and from his perspective the trip lasts just 1 year. However, the clock of the twin who stays home ticks off 30 years while his brother is away. When the traveling twin arrives back home, he finds that his brother has aged 30 years.

Most theoretical explanations of time travel assume that a highly advanced civilization could overcome the insurmountable technological problems of designing spacecraft that could fly at near the velocity of light, where time dilation is most pronounced. Science fiction accounts, therefore, have time travelers hurtling through space at nearly the speed of light; in some cases their journeys last billions of earth years.

But do we live in a universe where such travel is actually possible? Are the clocks in living cells like mechanical clocks, and will they slow down at high speeds?