An interesting article in Scientific American Reports’ special Astropohysics edition , written by Paul Davies, discusses how it could be possible to build a time machine.
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The theories on how this is possible already exist, however the implementation of these is beyond our current scientific abilities. The following explains some of the current theories and concepts.
Time isn’t constant
Most people believe that everyone experiences time in exactly the same way, regardless of the physical circumstances present. The truth is that this isn’t the case.
Einstein, in his theories of relativity, postulated that the measured time interval between two events, would depend on how fast the observer would be moving. This hypothesis has been proven by various methods.
The problem is that on Earth, the amount of speed needed to alter the time effect, just isn’t applicable to us, in an everyday sense. Tests have shown that travel by plane, increases a second by a few nanoseconds.
In the laboratory, subatomic particles called muons, have been propelled at light speed in atomic generators, and have shown that their rate of decay slows dramatically in respect to their higher velocities.
The author cites that cosmic rays, from outer space, can reach us on earth, because the resulting speed of these rays reduces their rate of decay, allowing them to reach us and be seen by us.
Dramatic time warps start occurring near the speed of light. Mr. Davies gives an example of this phenomenon, by stating that if twins are born at the same time, and one travels at the speed of light for a year before returning to earth, the traveling twin would be one year old, while the earthbound twin could have aged 10 earth years.
The paradox here is that, although they are twins, they would have different ages at this point.
We have now discussed one theory on time travel to the future. By traveling fast, namely the speed of light, time will slow down for us, while continuing at a normal pace elsewhere.
Theoretically, calculations could be made to jump to a specific time and point in the future. It is also known that gravity slows down time as well. We know that time goes by faster in space than here on earth, because we are closer to the earth and the earth’s gravitational pull.
Subsequently, time in a submarine goes by even slower than those on land, for the same reason. Scientists have calculated that a neutron stars’ gravitational pull is so strong, that it slows time down by thirty percent.
Scientists feel that if an astronaut could zoom very close to a neutron star or black hole for that matter, he could leap far into the future.
Going to the past poses a more difficult problem. One theory postulated by Kurt Godel states that the universe rotates and that its gravity affects light. This rotation of the universe would drag the light and the relations between objects, around with it.
By traveling in this closed loop of time, without exceeding the speed of light, it could be possible to visit the past. One of the more accepted scientific scenarios for travel to the past, however, involves the concept of a wormhole.
A wormhole is a shortcut between two points in space. Scientific movies, such as the movie Contact and the author Carl Sagan have used this scenario as a time travel device. The difficulty lies in making the wormhole.
It would have to be found in space as an actual entity, or manufactured on earth. Once found or made, it would have to be enlarged and maintained. Negative energy would have to be produced to ensure the patency of the wormhole and allow for safe travel through it.
The wormhole would need to be transported to a place where the opposite mouths are kept apart. One mouth would be positioned near a sun or neutron star, while the other would be in a non-gravitational point in space.
The gravity of the neutron star would slow time down, effectively creating two different points and times in space. Direction of travel could then determine whether one goes to the future or to the past.
Two prominent physicists have made two other theoretical proposals for time travel. In 1994, a Mexican physicist Miguel Alcubierre wrote an article for the Journal of Classical and Quantum Gravity, proposing that space could be stretched and in part contracted, by waves.
This is known as the Alcubierre metric. The spaceship would ride the wave and be inside what is called a warp bubble. The ship would not be traveling at the speed of light, but would still arrive theoretically sooner than one that would travel at that speed, due to the contraction of the space ahead of it.
The problem of course is that there are no known ways of creating warp bubbles and space contraction. In 1991 a Princeton physicist, Richard Gott, proposed another theory on time travel.
He suggested that string-like objects in space, known as cosmic strings, formed in the early universe, may line up and traverse its entire length. These strings are thinner than an atom.
They are under great pressure and can generate a tremendous amount of gravitational pull. By placing two strings together or placing them near a black hole, space may be able to be warped, allowing objects connected to these strings to travel at tremendous speeds, into the past.
Although these theories are thought provoking, there are many other questions that still need to be answered. One such question revolves on whether going back in time could effect earth history?
Steven Hawkings has proposed that this may not happen with his “chronology protection conjecture”. Of course these are problems we don’t need to face yet. As we advance technologically, many of these questions will need to be addressed, before man ventures into the unknown of space and time travel.