 | Martin Ratcliffe
is President, International Planetarium Society (2001-2002) and Director of Theatres and Media Services at Exploration Place and has been involved in all aspects of program development for the Boeing Cyberdome Theater and the Simulation Center. The CyberDome theater continues development of fully interactive shows in immersive domed theatres. Prior to moving to Wichita, he directed the Buhl Planetarium at the Carnegie Science Center in Pittsburgh, PA from 1991 to 1997. Martin co-developed the world's first interactive Planetarium in Armagh, N. Ireland. Martin is also an accomplished writer and monthly columnist for the national magazine, "Astronomy". He also films total eclipses of the Sun for television, and enjoys astrophotography. He is a past Council member of the British Astronomical Association. He earned his Bachelor's of Science degree from University College London (England) in Astronomy. Martin is adjunct professor of Astronomy at Baker University in Wichita, Kansas. |
Astronomy
2003-04-01 05:59:00
forever
Let's begin by explaining what light actually is, and then discuss why we can't travel at the speed of light. It was Scotsman James Clerk Maxwell who, in the 1860's, came up with a set of equations that described electricity and magnetism in one coherent theory. Out of his mathematical theory came a fixed number that was the speed of electromagnetic waves, or light, and thus he managed to explain light as an electromagnetic wave. Light travels at about 670,000,000 miles per hour, or 186,000 miles per second (in a vacuum).
Maxwell's electromagnetism theory predicted the existence of other electromagnetic waves that all travel at the same speed. It was not until some years later, in the 1880's, that radio waves were discovered. Since then, of course, x-rays, ultraviolet, infra-red and the ubiquitous microwaves have been recognized as different varieties of light and have been put to every day use. We have much to thank Maxwell for in today's modern society. Such is the power of a real scientific theory in that it predicts what you might discover in the future that has previously been unseen.
One attribute of his theory is that light always travels at the same speed in a vacuum, irrespective of the speed of the object emitting it. While this seems counterintuitive in our unique Earth-bound experience, numerous experiments have shown that the theory accurately describes how light behaves.
Consider a baseball pitcher who fires a baseball at 90 mph from the front seat of a car speeding along at 60 mph. The resulting speed of the baseball would be 150 mph. But, if you are on a spaceship traveling at half the speed of light and you shine a light out front, the light would still travel at the speed of light and not, as you may expect, at one-and-a-half times the speed of light.
Testing this prediction led to one of the most famous experiments of all time, the Michelson-Morley experiment. At the end of the 19th century, Albert Michelson and Edward Morley set out to find if the Earth's speed along its orbital path around the Sun had any effect on the speed of light. A single beam of light was split and bounced back and forth between mirrors. One set of mirrors was at right angles to a second set, so that one light path was along the same direction as Earth's motion and the other perpendicular to it. If the speed of light varied, the experiment would detect the change, but none was seen.
Enter Albert Einstein. His theory of relativity used Maxwell's idea of a constant speed of light to turn our common sense view of the universe on its head and explain the appearance of the world in a whole new way. Einstein's theory of general relativity (essentially a theory of gravity) shows that light is the one universal constant in the universe.
His theories made many predictions, one of which was that as you approach the speed of light, your mass increases (and your length shrinks). Since it takes energy to accelerate a mass, more and more energy is required to accelerate faster. As you approach the speed of light, your mass increases toward infinity, consequently requiring an infinite amount of energy to accelerate any faster. So the speed of light represents a physical limit in today's universe. But what is more amazing is that Einstein's theory of Gravity (relativity) of nearly one hundred years ago have stood the test of time and have passed every test. Application of his theory has a place in our lives today as our reliance on space-based technology increases.
