Reading aloud Light reveals all the secrets of the world. From the firefly to the big bang: Photons illuminate the nature of both the microcosm and the macrocosm. They transfer energy and information - and they make life possible. The researchers now know about the birth of the first light, perhaps 15 billion years ago. It was created by the heat of the Big Bang and the destruction of matter and antimatter in the first seconds of the cosmos. Even the number of photons in the observable universe can be estimated: around 1089 - a billion times more than the number of atoms.

Light is still being reborn: by nuclear fusion at 10 to 150 million degrees inside the stars. From there, however, it can not fly straight out, but - as in the young universe - is constantly distracted by swirling electrons and atomic nuclei. Thus, in a century-long zigzagging course, it has to fight its way to space. From the surface of our sun, the light needs only eight minutes to the earth. When sunbathing, ten billion photons per second patter on every square centimeter of skin. Other particles of the solar wind, mainly electrons and protons, travel 20 to 50 hours. Although the terrestrial magnetic field largely shields them - but sometimes some bounce on the atmosphere. Then they provide - especially in high northern and southern latitudes - for furious auroras. Their blue and violet colors are created by excitation of nitrogen atoms in the air, green comes from the oxygen. Polar lights have also been observed in the planets Jupiter and Saturn.

However, light is not only created by the burning up of matter at high temperatures. Nature also brings cooler luminous phenomena. For example, the fluorescence: Some atoms or molecules swallow energy, are thereby put into an excited state and release this energy within a millionth of a second as light again. For example, television screens and fluorescent tubes are based on this principle. Chemical additives in detergents fluoresce bluish in the ultraviolet of daylight; this blue adds up to the yellow of lime residues and gives "bright white".

Living things too can produce light in a cold way - a process known as bioluminescence. It requires energy and the catalytic activity of specific enzymes, the luciferases. They oxidize certain carbon compounds, the luciferins, producing a bluish or green glow. Some insects and fish have their own light cells, which are often lined with reflective crystals. From these cells, the organic light shines through the skin of the animals. So they can communicate with each other or attract nutritious animals. display

For example, light is also used to find partners. In a warm June night, fireflies sparkle in the rush of love: the male insects dance through the air, while the females, known as the fir or locust worm, sit expectantly in the grass and fly back with a bright behind. For some males of the genus Photinus, however, the love dance ends fatally. Because females of the fireflies genus Photuris mimic the flirting signals of the Photinus ladies - and like the light-headed Photinus males to eat.

=== Rüdiger Vaas

© science.de

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