TIME TRAVEL 219
could never deviate from its past One second on the Earth was one
second throughout the universe. This conception was overthrown by
Einstein, who showed that time was more like a river that meandered
across the universe, speeding up and slowing down as it snaked across
stars and galaxies. So one second on the Earth is not absolute; time
varies when we move around the universe.
As I discussed earlier, according to Einstein's special theory of relativity, time slows down inside a rocket the faster it moves. Science fiction writers have speculated that if you could break the light barrier,
you could go back in time. But this is not possible, since you would
have to have infinite mass in order to reach the speed of light. The
speed of light is the ultimate barrier for any rocket. The crew of the Enterprise in Star Trek IV: The Voyage Home hijacked a Rlingon spaceship and used it to whip around the sun like a slingshot and break the
light barrier to wind up in San Francisco in the 1960s. But this defies
the laws of physics.
Nonetheless, time travel to the future is possible, and has been experimentally verified millions of times. The journey of the hero of The
Time Machine into the far future is actually physically possible. If an
astronaut were to travel near the speed of light, it might take him, say,
one minute to reach the nearest stars. Four years would have elapsed
on the Earth, but for him only one minute would have passed, because
time would have slowed down inside the rocket ship. Hence he would
have traveled four years into the future, as experienced here on Earth.
(Our astronauts actually take a short trip into the future every time
they go into outer space. As they travel at 18,000 miles per hour above
the Earth, their clocks beat a tiny bit slower than clocks on the Earth.
Hence, after a yearlong mission on the space station, they have actually journeyed a fraction of a second into the future by the time they
land back on Earth. The world record for traveling into the future is
currently held by Russian cosmonaut Sergei Avdeyev, who orbited for
748 days and was hence hurled .02 seconds into the future.)
So a time machine that can take us into the future is consistent
with Einstein's special theory of relativity. But what about going backward in time?
could never deviate from its past One second on the Earth was one
second throughout the universe. This conception was overthrown by
Einstein, who showed that time was more like a river that meandered
across the universe, speeding up and slowing down as it snaked across
stars and galaxies. So one second on the Earth is not absolute; time
varies when we move around the universe.
As I discussed earlier, according to Einstein's special theory of relativity, time slows down inside a rocket the faster it moves. Science fiction writers have speculated that if you could break the light barrier,
you could go back in time. But this is not possible, since you would
have to have infinite mass in order to reach the speed of light. The
speed of light is the ultimate barrier for any rocket. The crew of the Enterprise in Star Trek IV: The Voyage Home hijacked a Rlingon spaceship and used it to whip around the sun like a slingshot and break the
light barrier to wind up in San Francisco in the 1960s. But this defies
the laws of physics.
Nonetheless, time travel to the future is possible, and has been experimentally verified millions of times. The journey of the hero of The
Time Machine into the far future is actually physically possible. If an
astronaut were to travel near the speed of light, it might take him, say,
one minute to reach the nearest stars. Four years would have elapsed
on the Earth, but for him only one minute would have passed, because
time would have slowed down inside the rocket ship. Hence he would
have traveled four years into the future, as experienced here on Earth.
(Our astronauts actually take a short trip into the future every time
they go into outer space. As they travel at 18,000 miles per hour above
the Earth, their clocks beat a tiny bit slower than clocks on the Earth.
Hence, after a yearlong mission on the space station, they have actually journeyed a fraction of a second into the future by the time they
land back on Earth. The world record for traveling into the future is
currently held by Russian cosmonaut Sergei Avdeyev, who orbited for
748 days and was hence hurled .02 seconds into the future.)
So a time machine that can take us into the future is consistent
with Einstein's special theory of relativity. But what about going backward in time?