Thorne believes there could be another type of tunnel-like structure existing
in the universe that could be used for a time travel portal. Wormholes, also
called Einstein-Rosen Bridges, are considered to have the most potential for
time travel if they do exist. Not only could they allow us to travel through
time, they could allow us to travel many light-years from Earth in only a
fraction of the amount of time that it would take us with conventional space
Wormholes are considered possible based on Einstein's theory of relativity,
which states that any mass curves spacetime. To understand this curvature, think
about two people holding a bed sheet up and stretching that sheet tight. If one
person were to place a baseball on the bed sheet, the weight of the baseball
would roll to the middle of the sheet and cause the sheet to curve at that point.
Now, if a marble were placed on the edge of the same bed sheet it would travel
down toward the baseball because of the curve.
Imagining space as a curved two-dimensional plane, wormholes like this
could be formed by two masses applying enough force on spacetime to create a
tunnel connecting distant points in the universe.
In this example, space is depicted as a two-dimensional plane rather than the
four dimensions that actually make up spacetime. Imagine that this sheet is
folded over leaving a space between the top and bottom. Placing the baseball on
the top side will cause a curvature to form. If an equal mass were placed on the
bottom part of the sheet at a point that corresponds with the location of the
baseball on the top, the second mass would eventually meet with the baseball.
This is similar to how wormholes are likely to form.
In space, masses that place pressure on different parts of the universe could
eventually come together to form a tunnel, this is a wormhole. We could then
travel from Earth to another galaxy and back relatively quickly (within a
lifetime). For instance, let's picture a scenario in which we would want to
travel to Sirius, a star that's seen in the Canis Major constellation just below
Orion. Sirius is about 9 light-years from Earth, which is about 54 trillion
miles (90 trillion km). Obviously, this distance would be far too long for space
travelers to traverse and return in time to tell us about what they saw there.
So far, the farthest people have traveled into space is to the moon, which is
only about 248,548 miles (about 400,000 km) away from Earth. If we could find a
wormhole that connected us to the space around Sirius, then we could cut the
time considerably by avoiding the trillions of miles that we would have to cross
with traditional space travel.
So how does all this relate to time travel? As we discussed earlier, the
theory of relativity states that as the velocity of an object nears the speed of
light, time slows down. Scientists have discovered that even at the speeds of
the space shuttle, astronauts can travel a few nanoseconds into the future. To
understand this, picture two people, person 1 and person 2. Person 1 stays on
Earth, while person 2 takes off in a spacecraft. At takeoff, both of their
watches are in perfect sync. The closer person 2's spacecraft travels to the
speed of light, the slower time will pass for person 2 (relative to person 1).
If person 2 travels for just a few hours at 50 percent the speed of light and
returns to Earth, it will be obvious to both people that person 1 has aged much
faster than person 2. This difference in aging is because time passed much
faster for person 1 than person 2, who was traveling closer to the speed of
light. Many years might have passed for person 1, while person 2 experienced a
time lapse of just a few hours. Read more about this twin paradox in How Special
If wormholes could be discovered, it might allow us to travel to the past as
well as the future. Here's how it would work. Let's say the mouth of the
wormhole is portable. Then person 2 in the example above who traveled at 50
percent of light speed into space for a few hours could carry one wormhole mouth
into space, while the mouth at the opposite end of the wormhole would stay with
person 1 on Earth. The two people would continue to see one another as person 2
traveled into space. When person 2 returns to Earth a few hours later, a few
years may have passed for person 1. Now, when person 1 looks through the
wormhole that traveled into space, that person will see him or herself at a
younger age, the age he or she was when person 2 launched into space. The cool
thing about it is that the older person 1 would be able to step into the past by
entering the wormhole, while the younger person 1 could step into the future.
Black Holes, Wormholes and Cosmic Strings
While writers have produced some great ideas for time machines over the years, a
real life time machine has yet to be built. Most theories of time travel don't
rely on machines at all. Instead time travel will likely be done by way of
natural phenomena that will transport us quickly from one point in time to
another instantly. These space phenomena, which we are not even sure exist,
Rotating black holes
Rotating Black Holes
Photo courtesy NASA
When stars that are more than four times the mass of
our sun <http://www.howstuffworks.com/sun.htm> reach the end of
their life and have burned up all of their fuel, they collapse under the
pressure of their own weight. This implosion creates "black" holes, which have
gravitational fields so strong that light cannot even escape. Anything that
comes in contact with a black hole's event horizon will be sucked in. The event
horizon is the boundary of a black hole at which nothing can escape.
You can think of the shape of a black hole as similar to an ice cream cone.
It is large on top and tapers into a point, called a singularity. At the
singularity, the laws of physics cease to exist and all matter is crushed beyond
recognition. This kind of non-rotating black hole is called a Schwarzschild
black hole, named after the German astronomer Karl Schwarzschild.
Another type of black hole, called a Kerr hole, is also theoretically
possible. Kerr holes are rotating black holes that could be used as portals for
time travel or travel to parallel universes. In 1963, New Zealand
mathematician Roy Kerr proposed the first realistic theory for a rotating black
hole. In his theory, dying stars would collapse into a rotating ring of neutrons
which would produce sufficient centrifugal force to prevent the formation of a
singularity. Since the black hole would not have a singularity, Kerr believed it
would be safe to enter it without being crushed by the infinite amount of
gravitational force at its center.
If Kerr holes do exist, it might be possible to pass through them and exit
out of a "white" hole. A white hole would have the reverse action of a black
hole. So, instead of pulling everything into its gravitational force, it would
use some sort of exotic matter with negative energy to push everything out and
away from it. These white holes would be our way to enter other times or other
Given the little we know about black holes, Kerr holes may possibly exist.
However, physicist Kip Thorne of the California Institute of Technology
believes that the laws of physics prevent such a formation. He says there is no
such way to enter and exit a black hole, and that anything attempting to enter a
black hole will be sucked in and destroyed before it even reaches the
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