Black holes are a perilous way to travel. Apart from the
dangers of spahettification and collisions with singularities, the tunnel
that connects a black hole to another universe stays open only briefly
and then collapses. But there may be an alternative, although at the moment
it exists only in theory. One day, scientists may be able to turn off the
fury of a black hole using antigravity - the opposite of gravity - to create
a wormhole. A wormhole has two mouths, connected by a tunnel through curved
space. Unlike the event horizon of a black hole, the mouth of a wormhole
allows two-way traffic: you can enter and leave. And a wormhole also has
the great advantage that it can connect different parts of our own Universe,
providing a safe shortcut between two distant places.
Making your own wormhole
It is one thing to keep an existing wormhole open, but
there may not always be one to take you where you want to go. The answer
is to create one. Make a hollow in space until your destination is close
to the base of the hollow. Make a small hole in the base of the hollow,
and another next to your destination. Glue the edges of the holes together.
You have made your own personal wormhole, and are free to travel the Universe.
Holding A Wormhole Open With Antigravity
The tunnel formed between the two mouths of a wormhole
is stable: it will not pinch off. But how do we ensure that the tunnel
remains open? The trick, according to Kip Thorne, is to reinforce the walls
of the tunnel with some sort of exotic material that pushes the wormhole's
walls apart. Instead of having gravity, this material must exert antigravity,
which forces everything away from it. Thorne believes that, one day, an
extremely advanced society will develop the know-how to make an antigravity
material.
Straight-Line Shortcut
A wormhole can provide a swift, straight-line route between
two parts of our Universe, no matter how far apart they are. Since space
can be curved , or folded, the length of the wormhole can stay the same,
whether connecting distant or close parts of the Universe. Going by wormhole
is far quicker than travelling at the speed of light to very distant parts
of the Universe.
One Small Step Into A Wormhole
It's the 25th century. At the Kennedy Space Center, Cape
Canaveral, a NASA scientist is preparing to go to work. But he won't be
using a rocket. No one has for centuries - which is why NASA's armada of
launch vehicles sits gently rusting away on the tarmac, a memorial to the
quaint, bygone days of rocketry. Instead, he kits himself out in his spacesuit
- and enters the waiting mouth of the specially constructed Kennedy Wormhole,
which is lined with antigravuity material. This "one small step for a man"
truly constitues a giant leap. Stepping into the entrance, the scientist
emerges in another world.
One giant leap across space
The NASA scientist emerges from the wormhole into the
Moon base. It has taken him no time at all to cross the 384,000 km that
separate the Moon from the Earth - a journey that took the Apollo astronauts
three days. Through the mouth of the wormhole, you can see the image of
the rusty rockets back on Earth. That's because light also travels through
the wormhole, although it is distorted by the antigravity material pushing
the light beams apart. Look at the picture of the Kennedy Space Centrer
on the opposite spread, and you'll see the corresponding image of the Moon
base through the other wormhole mouth.
Created on a car journey
Kip Thorne, an American physicist, was the first person
to suggest, in 1985, that wormholes might be used for space travel. Asked
by astronomer Carl Sagan to help with his novel Contact, Thorne solved
the problem on a long car journey. Sagan planned to transport his heroine
to the star Vega - 26 light years away - via a black hole. Halfway along
Interstate 5, Thorne realized that the only safe way was by wormhole.
Time travel
One day black holes may give us a means of travelling
through the exotic reaches of space - and possibly into other universes.
They may even provide the key to making a journey through time. To be a
time traveller, you need a "tamed" black hole: a wormhole. The idea of
time travel through a wormhole does not seem so far-fetched when you consider
that wormholes are shortcuts to very distant places in curved space. They
take you to a remote location in almost no time at all, so it is like travelling
faster than the speed of light. And Einstein's special theory of relativity
says that if something is able to travel faster than light, it will move
backwards through time. So wormholes may be the gateways into the past.
Follow the scientist's weird experiences as he creates a time machine using
a wormhole.
1) Starting From Earth
An igenious young scientist on Earth decides to construct
a time machine. First, he makes a wormhole. He attaches one end of it to
the Earth, and the other to an unmanned spacecraft. Next, he launches the
craft so that it sets off across space at a condsiderable fraction of the
speed of light. He has programmed the spaceship to return later on. Now,
all he has to do is sit back and wait....
2) Out Steps the future
At age 30, the scientist finds an aged man climbing through
the wormhole, followed by a gang of futuristically clad children. He is
face-to-face with himself, aged 70.
3) Stepping into the past
Fifty years after its launch, the spacecraft lands in
the 70-year-old scientist's backyard - still with its wormhole attached.
Because of special relativity, only 10 years have elapsed onboard the spaceship.
This means that the wormhole's other mouth is joined to the Earth as it
was 10 years after launch - 40 years ago. It the scientist steps through
the spacecraft's wormhole, he can travel back through time and meet himself
at the age of 30.
The twins paradox
We are all travelling into the future as time passes,
but Einstein's theory of special relativity can provide a shortcut through
time. Start with a pair of twins. While one remains on Earth, her astronaut
sister blasts off into space at almost the speed of light. Relativity tells
us that the faster an object moves, the slower time on it appears to pass
- an effect known as time dilation. When the speeding astronaut returns,
she has hardly aged, while her twin on Earth is an old woman. This method
cannot, however, take us back into the past.
Wormhole to the past
Combine the "twins paradox" with a wormhole, and you
could create a time machine that allows us to travel both ways in time.
Kip Thorne suggests attaching one end of a wormhole to a speeding spacecraft,
while the other end stays on Earth. In this example, 50 years pass on Earth
before the spacecraft returns. But on the spaceship, only 10 years have
elapsed, so the wormhole connects the spacecraft with the Earth as it was
40 years earlier. By stepping onto the spacecraft and through the wormhole,
future humans could travel decades back into the past.
Grandmother paradox
A mad scientist, intent oon evil deeds, creates a wormhole.
Travelling back in time through the wormhole, he finds his grandmother
as a young girl - and kills her. But if he killed his grandmother, then
she would not have been able to give birth to the scientist's mother. She,
in turn, could not have given birth to the scientist. The scientist wouldn't
exist - so how could he go back in time and murder his grandmother? Such
paradoxes prompt some scientists to declare time travel must be impossible.
Shape of time machines to come
Scientists have dreamed up other kinds of time machines,
but these are even more far-fetched than wormholes. One idea is to make
and infinitely long cylinder and to spin it extremely rapidly. Another
involves exotic (and as yet undiscovered) entities called "cosmic strings
- thread-like tubes of concentrated energy formed in the very early Universe.
It two cosmic strings are swiftly moved past each other, they affect spacetime,
and might allow time travel. It is also possible that a spinning naked
singularity could be a time machine.
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