Worlds of David Darling > Children's
Encyclopedia of Science > Could You Ever Fly to the Stars? > 3. Through
the Light Barrier
COULD YOU EVER FLY TO THE STARS?
a book in the Could You Ever? series by David Darling
3. Through the Light Barrier
The fastest that most people ever travel on Earth is about 600 miles per
hour, the cruising speed of a large airliner. Compare this with the 670
million miles per hour of a light ray, and it is clear that we have no experience
of really high speeds at all.
Still, we can use our common sense. The only effect of traveling very fast
would be to make the time of our journey shorter. Whether we travel at 5
miles per hour or 500 million miles per hour should not make any difference
apart from getting to our destination quicker. Isn't that right?
No – it is wrong. In 1905, the brilliant German scientist Albert Einstein
caused a revolution in the way we think about the universe. In his special
theory of relativity, he showed that quantities such as mass, length, and
time are not as fixed as they seem. In fact, very odd things start to happen
when objects move relative to one another at speeds close to that of light.
The Curious Case of the Mixed-Up Clocks
Suppose a spaceship makes a round trip to the nearest star, Proxima Centauri,
at a steady nine-tenths of the speed of light. (We will assume that it comes
straight back without stopping.) Then to everyone on Earth, the journey
will seem to have taken about 9½ years. Yet, according to clocks carried
aboard the spacecraft, only slightly more than 4 years will have gone by.
Incredibly , the astronauts will have aged 5½ years less than their
friends who stayed behind on Earth!
Strangely, as Einstein discovered, time slows down for objects traveling
at extremely high speeds. If someone on Earth with a powerful telescope
could watch the clocks aboard a fast-moving starship, those clocks would
seem to lose time. The faster the spacecraft went, the slower the clocks
would seem to tick. Even the astronauts would appear to do everything in
slow motion. Yet, from the astronauts own points of view, aboard the starship,
all would appear normal.
Other odd changes take place, too, at high speeds. As view from Earth, a
fast-moving spaceship would seem to shrink along its direction of motion.
Also, its mass would increase. At nine-tenths the speed of light, a spacecraft
would look less than half as long as it did at rest and twice as massive.
Yet to the crew, the ship would appear unchanged. To them, dust particles
and everything in space would appear more squashed together and more massive.
The changes that occur at such high speeds have an important bearing on
future travel to the stars. They make it possible for astronauts to visit
even very distant stars well within their own lifetimes. If the astronauts
travel fast enough, they will age much more slowly than if they had stayed
on Earth. For instance, a trip to a star 100 light-years away at 99 percent
of the speed of light would take more than a century as measured by Earth
clocks. But the astronauts who made such a journey would age by only 10
years. In starships that moved even faster, people could cross hundreds
or thousands of light-years in just a few years as measured by the clocks
aboard their spacecraft.
But when the crew returned from such a voyage, they would find that all
their friends and relatives had long since died. The crew members would
have aged by only a few years. Yet they would find that the Earth and everything
on it would be centuries older than when they had left. It is hard to imagine
that anyone would want to go back to a home planet that could no longer
On the Trail of the Starship Enterprise
In the language of Star Trek, "warp factor one" means the speed of light.
The starship Enterprise crashes through the light barrier with
ease. But will that ever really be possible? According to Einstein's theory
of relativity, the answer is no.
Einstein calculated that as an object gathers speed, it also gains mass.
The more massive something is, the harder it is to push it to still higher
speeds. Eventually, a time comes when the object has so much mass that it
is impossible to make it go any faster. In fact, to make a spaceship reach
exactly the speed of light would take more energy than there is in the whole
Einstein's theory does not mean that a starship could not go very close
to the speed of light. In principle, the interstellar ramjet could travel
at 99 percent, or even 99.999 percent, of the speed of light. But it could
never reach light-speed.
This limit on speed appears to mean that real starships cannot hop from
star to star at warp factor one – never mind warp factor eight or
nine. But there is one other possibility that may help us break through
the light barrier.
Into the Black Hole
There are some weird things in the depths of space. But perhaps the strangest
of all is the BLACK HOLE. A black hole is a place where the pull of gravity
is so strong that nothing can escape from it – not even light.
Black holes are thought to form when stars much heavier than the Sun reach
the end of their lives. When a massive star has used up all its available
fuel for making new light and heat, the outer parts of it are blown away
in a monstrous explosion called a supernova. The remains of the wrecked
star – its burned-out core – may then shrink in the wink of
an eye until it is smaller than the dot over this i.
Although the once-bright star has now become tiny, its gravitational pull,
close by, is very strong. From within a radius of about 10 miles of the
dead star, nothing can escape. This is the region of the black hole.
Scientists are not sure what black holes are like inside. They believe that
if a spaceship fell into the kind of black hole that forms when a big star
dies, that ship would be rapidly torn apart.
But there may be other kinds of black holes. Some of these may be much larger
and more massive. The gravitational pull of a supermassive black hole would
be extremely powerful. Yet, it might not prove as damaging to a spacecraft,
because the difference in the pull between one end of the spacecraft and
the other would be far less than in the case of a small black hole. A starship
might be able to enter such an object without being destroyed. If so, that
might create a remarkable opportunity. According to some suggestions, such
a black hole could be used as a way to jump instantly to other, perhaps
remote places in the universe.
At the moment it is just an idea. But black holes may be like the entrances
to subway tunnels that connect may different places in space and time. The
tunnels themselves are known as "wormholes." And just as a black hole could
be the way into a wormhole, a "white hole" could be the way back out. In
theory, a spaceship could travel along wormholes and pop up in a place tens
or even millions of light-years away from where it entered. That journey
could be made in a very short time. The spaceship might even appear in the
far future or in the past, and then travel back to its own space and time
by going back through the wormhole the other way. Traveling in this way,
the speed of light would no longer be a barrier. But if such a journey through
time and space is possible, it remains hundreds of years in the future.