Time Travel
In 1898 H. G. Wells wrote his most famous novel,The Time Machine. In this novel, a young Victorian invented a device that allowed him to travel into the future or the past. He travels 800,000 years into the future and finds a society very different from the one he was accustomed to, inhabited bythe Eloi and the Morlocks. The Eloi appear to live an idyllic life, but the time traveler discovers that there is a horrible price they must pay.
In Back to the Future (1985), Marty McFly inadvertently finds himself in the 1950s, his "modern" car an oddity in a rural field.Writers such as Wells used fiction to comment on their own society. However, serious paradoxes raised by time travel have led many to contend that it is impossible. For example, what if a time traveler accidentally killed his own father, long before he was born? Isaac Newton thought of time as an arrow, traveling in a straight line at constant speed. But Albert Einstein theorized that time was much more variable. To Einstein, time could slow down and speed up in strong gravitational fields or when an object was traveling at high speed. The faster we travel through space, the slower we travel through time, at least to a stationary observer. Einstein's equations of general relativity allow several varieties of time travel. For example, in a rotating universe, moving against the direction of rotation would be moving backwards in time. Our expanding universe does not have this property.
A more interesting time travel possibility is presented by rapidly rotating, massive black holes. Such a black hole does not have an event horizon, but appears to be a ring. Moving through the center of the ring might lead to a different place and time—a wormhole through space. Nevertheless, no physical process currently known by scientists can produce a black hole with enough rotational speed for this to happen. Even if it did occur, such an object might be unstable and it might collapse if anything did pass through its center.
Stephen Hawking once suggested that time travel must be impossible, because if it were possible, we should have had visitors from the future. Since we have never seen a tourist from the future, time travel must be impossible. However, others have suggested that this argument breaks down if tourists from the future are simply not interested in us, or that time travel might be possible but impractical because of the enormous amounts of energy required.
If time travel is possible after all, how do we deal with the paradoxes? One way is to postulate the existence of alternate realities. Quantum me-chanics teaches us that a given system can exist in two different states, and we do not know which one until we examine the system. So, if we were to travel back in time and prevent, say, the assassination of U.S. President John F. Kennedy, we would have created a parallel universe. We would have changed the past for someone else, but not us.
Black Holes (Volume 2);; Einstein, Albert (Volume 2);; Kennedy, John F. (Volume 3);; Science Fiction (Volume 4);; Wormholes (Volume 4).
Bibliography
Adler, Bill, ed. Time Machines: The Greatest Time Travel Stories Ever Written. New York: Carroll & Graf Publishing, 1998.
Gardner, Martin. Time Travel and Other Mathematical Bewilderments. New York: W.H. Freeman, 1988.
Hawking, Stephen. A Brief History of Time. Toronto: Bantam Books, 1988.
Herbert, Nick. Quantum Reality: Beyond the New Physics. New York: Anchor Books Doubleday, 1987.
Parker, Barry R. Cosmic Time Travel: A Scientific Odyssey. New York: Plenum Press,1991.
Internet Resources
"Sagan on Time Travel."Nova Online. PBS.<http://www.pbs.org/wgbh/nov a/time/sagan.html>.
"The Physics of Time Travel." Explorations in Science with Dr. Michio Kaku.<http://www.mkaku.org/time_ travel.htm>.
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