Now that the speed of light had been accurately measured, the question of the existence of ether still needed to be addressed. In 1887, a famous experiment was set up to determine if the presence of ether could be found. It was called the Michelson-Morley experiment, named after the two scientists who set it up. The reasoning behind the experiment went something like this. If ether is motionless in space, then any object moving through it, like the Earth, would encounter an ether wind blowing in the opposite direction. The Earth moves through space as it orbits the Sun. Physicists thought that the ether wind was blowing past the Earth at the same speed that the Earth orbited the sun.
Just in case you were wondering or didn't know what the speed of light and all electromagnetic waves was, it is 186,000 miles per second, or 299,800 kilometers per second, or 670 million miles per hour. This speed is constant; it never changes and is the universal measuring tool to establish the distance of all celestial bodies from earth.
The speed of this ether wind could be measured by using a light beam, since the speed of light is always constant. (I'll cover how they knew that in “Cracks in a Newtonian World.”) The idea was to measure the motion of the Earth with respect to the fixed ether by measuring the speed of light as it moved back and forth in different directions on the surface of the Earth. The ether wind would affect the speed of light waves, just like wind affects the speed of sound waves in the air. According to this theory, the speed of light would increase in some directions and decrease in other directions. When the various speeds were compared, it would be easy to calculate the speed of the Earth. Since the speed of light is a fixed velocity, any fluctuations in its speed would be accounted for by the ether wind.
Radiation is a process that occurs when the atoms and molecules within any form of energy undergo an internal change and is sent out as rays or waves through space. For example, you can feel heat radiating from a stove when you stand near it. Or when you stand in sunlight you can feel the heat and see the light radiating from the Sun. (It's those waves that make the ground look like it's moving.)
The experiment was set up very precisely, and carried out a number of times, but it was an utter failure. There was no ether wind discovered. But this failure ended up changing the face of physics. It forced physicists to rethink their ideas about the structure of the universe and this long-held cosmological belief was soon regarded as a quaint superstition. However, even though this particular experiment didn't show any sign of ether, it didn't stop some scientists from still believing in its existence. And an important point to remember is that any experiment is designed so that certain outcomes, within particular parameters, may or may not be found. Just because this particular experiment didn't show any signs of its existence, doesn't mean that another theory or experiment couldn't. The existence of ether still has yet to be solidly proved or disproved. It's just fallen to the side, because its existence isn't necessary for the many theories and mathematics of today's cosmology.
Once it was discovered that light was an electromagnetic wave, a number of other scientists and experimenters found more types of electromagnetic radiation. They established the terminology that helped to define the properties of electromagnetic waves. Here is a summary of some of the most significant discoveries:
To oscillate simply means to swing or move regularly back and forth. An electric current varies regularly between maximum and minimum values. An oscilloscope is an instrument that can visually display on a fluorescent screen the waveform of an electrical current. Oh yes, and you can oscillate yourself when you can't make up your mind about doing something.
Frequency describes the number of cycles per second that an electromagnetic wave or electric current oscillates. It is expressed in hertz. Our household current is usually 60 cycles per second, or 60 hertz. There is a direct relationship between frequency and wavelength. The shorter the wavelength, the higher the frequency.
Wavelength describes the physical length of an electromagnetic wave, from crest to crest, and is measured in meters. For example, low frequency signals have a wavelength of 10,000 meters, or about 6 miles. Microwaves are about 10 centimeters, or about 4 inches. Shorter wavelengths are measured in angstroms. An angstrom is equal to one hundred millionth of a centimeter. X-rays are one angstrom long and gamma rays are 0.001 angstroms. The light we see has wavelengths between 4,000 and 7,000 angstroms.
So there you have a brief list of the early discoveries that were made regarding some of the more common forms of electromagnetic radiation.
Excerpted from The Complete Idiot's Guide to Theories of the Universe © 2001 by Gary F. Moring. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.