from Lake Afton Public Observatory
Time travel has been the source of many science fiction stories for generations. Recently the idea of traveling in time has been given some surprisingly serious thought. Albert Einstein's theory of relativity has posed some very interesting questions about the realities of what we perceive as space and time. After all, one of the easiest things to do is to look back into time--just look into the night sky. The light you see from the distant stars is not how they appear today. In some instances, you are seeing the stars as they appeared thousands and even millions of years ago.
Much of what we call classical physics, which is more or less the physics of everyday experience, is based upon two foundations. The first of these is the laws of motion as described by Sir Isaac Newton. These laws are the fundamental building blocks by which we describe the motions we observe--whether here on Earth or in the heavens. But a careful look at these ideas reveals a fundamental, inescapable flaw. At the root of Newton's laws are the ideas of an absolute space and an absolute time--a center to the universe where no motion exists and time is perfect. The only problem with having this kind of center, according to Newton's own law of gravity, is if something were to bump into the center it would rip the universe apart--a major problem. The second foundation is based upon the work of the brilliant Scottish physicist, James Clerk Maxwell, who in 1865 published a beautiful mathematical description of the relationship between electricity and magnetism. The formulation of his ideas culminated in four equations. Derived from these equations is a basic relationship called the electromagnetic wave equation, which describes the motion and properties of a light wave. Contained within this equation is a fundamental constant that appears as a direct result of Maxwell's equations. It turns out that this fundamental constant is a velocity equal to the exact speed of light, denoted as "c". What this implies is that all electromagnetic waves, from radio to x- rays, travel at the same speed everywhere--seven times around Earth in one second. However, a speed needs to be measured with respect to something else! All attempts to find how light traveled with the speed c failed.
The solution to this most perplexing of all physics problems began to take shape in the mind of a 16 year old schoolboy from Ulm, Germany around the year 1895. A young Albert Einstein began to wonder what it would be like to ride (surf?) on the crest of a light wave. Ten years later, in 1905, Einstein would publish a paper called "On the Electrodynamics of Moving Bodies", which would rock the very core of physics and change our perception of reality forever.
Much of Einstein's theory of relativity seems at first glance to be counter-intuitive and just plain outlandish. No other theories have been so successful in describing and predicting the universe we see. If it weren't for the fact that every experiment to test the validity of relativity has confirmed what the mind of Einstein perceived, then we could disregard relativity as the stuff of which science fiction is made.
At the root of relativity is the postulate that all light travels at the speed c, regardless of the observers point of view. For example, if someone traveling in a car at 98% the speed of light (or .98c) were to turn her headlights on, she would see the light move away from the car at the speed of light and someone watching from the side would see the light travel at the speed of light--not .98c + c. If this were not the case, then the universe would be a much stranger place. One light wave could overtake another or an effect could precede a cause. In order for this to be the case other factors such as our ideas of space and time must give way.
Dimensions of length must change at very high speeds. Someone watching a meterstick traveling at near the speed of light would see the meterstick as being very short--perhaps a few centimeters long. Time must change as well. A second for the moving meterstick would seem like hours to the observer, which means that time travels slower for the speeding stick. What was obvious to Einstein was the interrelationship between space and time. Time was a variable just like any other dimension. The only real absolute anything is the constant speed of light.
One of the ramifications of Einstein's theory is the prediction of discontinuities in time and space called singularities. Relativity predicts places (or really non-places?) where time and space simply do not exist. A modern term for one such an idea is called a space-time wormhole, or simply a wormhole. It is a kind of tunnel, outside our dimensions, that could lead anywhere in space and time. If some way could be found to make the wormhole traversable (since mathematically a wormhole has a tendency to collapse), then it is theoretically possible to travel not only vast distances but also to travel forward or backward into time. Perhaps someone in the distant future will find a way to make a traversable wormhole, come back in time, and watch you read about the very idea. Who knows? One thing is certain: By opening up our eyes and minds to the boundless universe we can surely see that the possibilities for mankind's future are infinite.
Astronomy Magazine, June '92, "How to Make a Time Machine".
The Cosmic Frontiers of General Relativity, William J. Kaufmann, III.
Time-Life Books, Voyage through the Universe, "The Cosmos".
Nova Video Series, "It's About Time".
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