 Once we understood that light was electromagnetic waves with a wide range of frequencies created by accelerating electric charge, a great deal of research went into studying the nature of this radiation as it related to matter and temperature. Because all matter above absolute zero contains vibrating or oscillating molecules colliding with each other, all matter radiates. Take a look at this iron rod. On the right, where it's cool, it's radiating any infrared, so we can't see it. Its gray color is based on reflected light. As it heats up, it turns red, then orange, yellow, and at the hottest it is white. If we could get it hot enough, you'd see it turning blue. These colors are emitted, not reflected. The problem with studying the emitted radiation is that you can't separate out the reflected radiation. What you need is a body that emits without reflecting. Such a body is called a black body, and its radiation is called black body radiation. Here's an example of an early construction of such a device. It's a closed container with platinum interior walls and a small hole at one end. The ceramic exterior keeps the temperature constant throughout the device. Inside, it is literally filled with a wide array of three-dimensional standing waves emitted by the hot platinum walls. Any radiation entering the device through the small hole will have little chance of finding its way back out through the hole. So for all practical purposes, all the radiation that leaks out through the hole will be radiation emitted by the platinum walls of the device. This makes the hole itself a black body. We knew that the amount of radiation, its intensity, goes up with temperature. The question was, do all frequencies or wavelengths increase in intensity at the same rate? Here's how this is measured. A black body is heated to a known temperature. It radiates a beam out of the opening. We then pass this beam through a prism to separate the various wavelengths. As we move a detector across the output, we measure the intensity at each selected wavelength. Then repeat the process with ever-increasing temperatures. We see that three things happen. One, the object emits more radiation at all wavelengths. Two, the peak emission frequency shifts towards shorter, blue wavelengths. And three, the intensity drops precipitously as the wavelengths enter the ultraviolet range. Using Maxwell's equations and the laws of thermodynamics, physicists developed the equation that should describe black body radiation behavior. It's based on the assumption that each wave contributes equally to the total radiation energy and the electromagnetic spectrum is continuous. But the equation predicts an increase in intensity in the ultraviolet range, not the drop-off we see. This dramatic inconsistency between the theory and observation became known as the ultraviolet catastrophe. Something was dramatically wrong with our understanding. In 1900, Max Planck came up with a solution for black body radiation behavior that fit the observations. But he had to break with two universally accepted fundamentals. He proposed that electromagnetic wave energy was not averaged over a range of the frequencies. Instead, energy is a function of each wave's frequency. And he proposed that electromagnetic waves emitted by oscillating atoms are not continuous. Instead, they come in discrete multiples of a minimum quantity. In particular, he proposed that wave energy was described by the simple formula energy equals a constant times the frequency. The new constant, h, is now known as Planck's constant, the fundamental constant in quantum mechanics. Unlike the speed of light, that's a really big number, Planck's constant is a really small number. Remember that a joule was the energy needed to lift an apple one meter? Planck's constant is 66 billion trillion trillion times smaller than that. That's why we don't see the effects in everyday life.