If someone asks us how many colors is the rainbow? The most common is to answer without hesitation seven, and even list them: red, orange, yellow, green, blue, indigo and violet. But how much reality does this have? The truth is that these seven colors only exist because of Isaac Newton's beliefs. The physicist who revolutionized the history of science, when in 1704 he published Opticks his study on the decomposition of white light, listed seven colors to fulfill his belief in the law of seven.

The decomposition of white light, which Newton demonstrated through a prism, can be found in nature, achieving one of the most passionate effects for man throughout history: the rainbow. By extension, the seven colors in which Newton broke down the white light are the seven colors that when we are small they teach us to put in the rainbows that we draw.

The physics of the decomposition of white light, is today something obvious, although at the time involved many headaches to several physicists. According to the theory developed by René Descartes and purified by Newton, every time a ray of light passes through a small drop of water suspended in the atmosphere, it comes out refracted showing all the colors that make up visible light.

Why do we always talk about seven colors? The seven is a number with a strong superstition and associated mysticism. Isaac Newton, in addition to laying the foundations of modern physics, spent much of his life studying alchemy, and was a faithful believer in the law of sevens, as the law that governed the Universe.

A rainbow doesn't just have 7 colors, it's just that you can't distinguish the subtle differences between them. The colors of the rainbow range from ultraviolet, through the 7 colors that the human eye can see, to infrared.