The early beginning of black body radiation
In the late 19th and early 20th century a revolution in the understanding of the physical world took place and modern Physics evolved. Much of this revolution was inspired by studies about the nature of light. What was puzzling at the turn of the century was that some experiments seemed to show that light was a wave phenomenon involving energy propagated in the form of waves in some mysterious medium. Other experiments showed the existence of discrete particles carrying that energy. Those experiments were the ground of the black body radiation field. Of course this field is far more advanced today, but this was the beginning of everything.
Very early in the history of the human race (or other close relatives) people had observed that hot objects emitted light. Eventually curious people began to study the concept of the relationship between temperatures, the type of object, and the color of light emitted. At the same time these people also tried to understand the nature of light. Means of studying the nature of the various colors of light were developed (such as prisms and diffraction gratings) and it was soon realized that color seemed to be related to wave-length, implying that light was the result of waves in some mysterious substance, eventually referred to as “the aether”.
Discovery of light behavior
In the late 19th century the photo-electric effect was discovered. This phenomenon, in which electricity or the flow of electricity was caused by light, seemed to indicate that light was made up of discrete particles, which became known as photons. Physicists tried to envision a theoretical ideal light source which they called a “black body”. A black body absorbs and emits all frequencies equally. In order to approximate such an object that was not made up of any specific substance, they considered a hollow object with a small hole. At the beginning, the studies of black body radiation were only theoretical, but soon everyone realized that it had many useful applications in the everyday world.
Early in the 20th century a number of experiments seemed to show that the mysterious “aether” did not exist. However, other experiments made the particle theory of light also seem to not be correct. While studying the relationship between temperature and light, scientists had studied what made objects hot or cold and had theorized that temperature was related to the speed of the basic particles of matter that they called atoms and molecules. One the basic concepts held dear by physicists of the time demanded that the energy of the particles be averaged out as if it were equally divided between the particles. When this concept was applied to the photons in an ideal black body the resulting prediction for the “color” (or if you will, the black body radiation) of the emitted light did not agree with experiment.
the uses of black body radiation today
The way out of this problem was the development of one of the two revolutions in science that produced what is known as “modern physics”. The study of “black body radiation” was one of the most important questions leading to the development of quantum mechanics. Modern physics allows us to understand both very large phenomena and very small phenomena. For most of us, it is the way that these understandings apply to everyday phenomena that matters.
Having the knowledge of black body radiation well understood and reliable allows for the ability to accurately calibrate equipment used to measure temperatures from a distance. For many scientists and engineers, accurate measurement is considered to be the benchmark of good science, the cornerstone upon which all work must rest.
