There is no other person who had as great an impact on twentieth-century cosmology as Albert Einstein. And while there are many well-known physicists such as Neils Bohr, Werner Heisenberg, Max Planck, Erwin Schrödinger, and more recently, Steven Weinberg and Stephen Hawking, they all stand on the shoulders of Einstein's discoveries.
Even now at the beginning of the twenty-first century, Einstein's theories continue to reveal new information about the universe, both at the microcosmic and macrocosmic levels. His revelations about the structure of energy, the principles under which gravity works, the nature of light, the relativity of space and time, and the proof of the existence of molecules would lead into important discoveries by other physicists and cosmologists. The state that cosmology is in today, which you'll get a chance to see later on, owes much of its success to the theories put forth by Albert.
To begin this section, I would like to summarize the basic assumptions about the dynamic structure of the universe that all scientists at the end of the nineteenth century generally accepted:
Newton's laws of motion accounted for the movement of all physical objects. There are three of them, and briefly stated they go like this:
Within the next 50 years each one of these five assumptions was proven false. Einstein's special and general theories of relativity altered a few and the development of quantum mechanics changed the rest. There were two essential problems that classical physics couldn't seem to answer. The first one dealt with how heat was capable of producing light. And the second had to do with the constant speed of light. Let's take a look at each one of these, because out of these two problems quantum physics and relativity theory were born.
Before light bulbs were frosted they were clear, and you could see the insides. The filament in a bulb was visible and it carried an electric current. As the current was increased, the filament would begin to glow and produce light. The color of that light would also change. The higher the current in the bulb, the hotter the filament got. And the hotter it got, the more the color changed. The question was, why? What was responsible for the changing color of the light? All hot objects, such as electrified light bulb filaments and heated branding irons, emit light. And if the light they emit is passed through a glass prism, that light will spread out into the familiar colored bands of the rainbow. These colored bands are called a light spectrum.
Sunlight produces a balanced spectrum of colors. There are equal amounts of all colors present. That is why sunlight appears “white” or colorless. All objects, no matter what their chemical nature and composition, send out light with the same color balance, if these objects are heated to the same temperature. It was the change in the balance of colors in the spectrum that was producing the different colors observed in the light bulb filament and a heated iron poker. The balance depended on how hot the glowing object became.
As an object is slowly heated to higher temperatures its characteristic color changes in a very predictable manner. Cool objects give off no apparent light. A hot poker glows red and at higher temperatures it starts to glow orange-yellow. At still higher temperatures, it glows blue. To get an idea of just what this looks like, look at a burning match. You'll see that the flame has different colors running through it. The temperature of the flame is not the same throughout, the bluer colors being the hottest part.
The light spectrum is a series of colored bands of diffracted light that are created when white light is sent through a prism. The colors are arranged in order of wavelength from infrared to ultraviolet. An easy way to remember the order of colors is by the acronym Roy G Biv: R = red, O = orange, Y = yellow, G = green, B = blue, I = indigo, V = violet.
When the spectra from various objects are examined at different temperatures, you find that various colors are emitted in differing amounts. It is the shifting of these amounts of colors that changes the characteristic color of the glowing object. But as the object becomes hotter, its color becomes whiter and the spectrum becomes more balanced. Everyone believed that the connection between the temperature of a material and the color of light had to be a mechanical one. After all, the rest of the universe was believed to be just as mechanical.
After Maxwell's success in explaining that a light wave is an electromagnetic oscillation, scientists began to suspect that the different colors of light emitted in a heated object were caused by the different vibrational frequencies. So red light was thought of as having a lower vibrational rate or frequency than blue light. This led to the assumption that the light energy emitted by a glowing body should tend to be given off at a higher frequency rather than a lower one. This is based on an idea called light wave economics.
The inability for classical physics to explain the color change of heated objects is known as the “ultraviolet catastrophe.” The problem is that if radiation is explained in terms of waves, using the same theory that describes sound waves, only the brightness of the light should change with temperature. The color should remain the same.
This idea simply expresses the relationship between the frequency of a wave and its length. Do you remember what that was? The higher the frequency of a wave, the shorter its length. And this related to a geometric factor that influences any glowing object. In other words, this geometric factor states that there are more ways for short waves to fit into any volume of space than for long waves. Light waves with very short wavelengths are able to take advantage of the space they find themselves in. And the geometric factor should produce short waves rather than long waves, or high frequencies rather than low ones.
What this meant was that heated objects should all produce light of very high frequencies, in the ultraviolet, x-ray, and Gamma range. There should be no change in color, only of intensity or brightness. But this obviously wasn't what everyone saw when objects got heated up. Things weren't their characteristic color and then all of a sudden became white hot. As long as light was considered to be a wave and thus mechanical, classical physics and Maxwell's mathematics could not explain light from heated bodies. Light energy would have to be considered to be something other than a wave. Max Planck and Albert Einstein would find the answer. You'll read all about their discoveries in “Famous Equations and Pools of Jell-O,” and, “That Old Quantum Theory.”
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.