The history of quantum physics began with Max Planck and his correct description of the radiation observed by a very specific device: the black body . Let’s see what this is about.
Historically, a black body has been described as a cavity that admits the entry of light through a single entrance hole , but does not let any of this original light escape. In this definition, something esoteric for many tastes, we have the feeling of being in front of a kind of black hole of light. However, unlike cosmological black holes, the black body is not so mysterious because eventually it did end up emitting radiation through its surface .
The fact that the original light does not come out again through the mentioned hole is simply due to a geometric trick , nothing more, nothing less. It is as follows: if the beam is incident at a small angle, it is highly unlikely that it will be reflected again by the only available aperture , since this is very small (see figure). If you think about it carefully, the black body , in this original conception, is rather a valve of light in which the original beam ends up being engulfed, without the ability to escape through reflections. However, as we said, the cavity heats up little by little and its energy is re-emitted throughout the surface in a homogeneous way and in many wavelengths (or frequencies): visible, microwave, radio, ultraviolet , etc.
A more modern and understandable definition for all would be related to a receptacle that is heated in some way (incandescent resistance, water bath, etc.) and through which the radiation is now emitted through the exit hole (which previously served as an entrance). . There are even companies specialized in the manufacture and distribution of these types of black bodies. The current utility of these devices is, among others, the calibration of optical sensors , since black body radiation is known with very high precision.
But after all, a black body is nothing more than anything that emits radiation when heated . This radiation can be even in the visible, so that they would have little black. For example, the Sun or an incandescent bulb are actually black bodies.
Alberto Corbi is a professor at the Higher School of Engineering and Technology (ESIT) of the International University of La Rioja (UNIR)
