2009-03-03 09:00:00
We are not aware of it but our vision of the world is a hoax, an illusion created by each object and its peculiar way of behaving in light.
A red dress we could say that it is of all colors, except red. When the white light, which is the set of all the colors of the rainbow, falls on it, the dress rejects the red and stays with all the others. If we illuminate the dress with green light only, it will not reflect any color, for us it will be black.
Our limited sense of sight is to blame for the deception, at least in part. We look through a window because the glass is transparent to the colors that we can see, however it is opaque to the radiations that we do not see, those that are below red (infrared) or beyond blue (ultraviolet). If our sense of sight could see infrared, we would have to change the glass in the windows.
Other bodies do not reflect light, they generate it; are light sources, a light bulb or a star are good examples. These objects glow more or less and it seems to us that we can reduce the intensity of the light at will, making it dimmer and dimmer to infinity. Another lie.
It was the German scientist Max Planck who discovered this other trick of Nature and, in doing so, revolutionized our view of the world. Energy, it was thought before him, is continuous and we can divide it into as small pieces as we want. Planck discovered that it was not.
The game of absorption and emission of energy that shapes our world was particularly attractive to scientists at the end of the 19th century. It was clear to them that visible light, infrared or ultraviolet radiation are just different aspects of a type of emission that receives the generic name of “electromagnetic radiation”. They also knew that if a body absorbs radiation it heats up and, on the other hand, a hot body emits radiation.
What the scientists of those days did not know is how each material emits radiation. To find out, they came up with a game: they devised a theoretical body capable of absorbing all radiation, a black body.
And black body It resembles a hermetic oven, perfectly insulated, inside which the walls absorb all the radiation without letting anything escape. Said like this we have a problem: we cannot see what happens inside. To find out, there is no other choice, we have to open a small hole.
If we open a hole to look, the external radiations will be able to enter through it, they will add energy to its interior and the body will heat up. The same thing happens when we put on black clothes in the sun, the clothes absorb the energy and we start to sweat. So, as we have said that a black body it is a perfect absorbent, the accumulated energy will increase and it will get hotter and hotter.
There cannot be a body capable of accumulating energy to infinity because it would end up stealing all that exists and the Universe would freeze to death. Impossible. If we open a hole, we also open an escape door for radiation. The black body is, at the same time, a perfect absorber and a perfect emitter.
In 1859, Kirchhoff, who would later be Max Planck’s teacher, carried out a series of experiments heating a furnace and measuring the emission coming out of a hole. It was the closest thing to the emission of a black body but the results were difficult to interpret.
It was in 1900 when Max Planck found the key to the problem and he did it with a revolutionary vision: Radiation is not emitted continuously, it goes in very small but indivisible packages that he called “quanta”. With that premise he deduced the formula that precisely matches the black body experiments and forever changed the world view of the tiny. he was born the quantum world.
We invite you to listen to the life of Max Planck. It starts this way:
On the last day of July 1945, an American officer rang the doorbell of a desolate and demolished house from the ravages of war. The door was opened for him by an old man with sad eyes and almost 90 years old, who moments before had been playing the piano to recover the will to live. Seeing him, the soldier greeted him with a solemn gesture. He was facing Professor MAX PLANCK, the most respected physicist in Germany; a man of impeccable integrity whom he had to transfer, for security reasons, out of Berlin…
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