The Sun, The Stars And The Birth OF Matter

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THE SUN, THE STARS AND THE BIRTH OF MATTER

“Lernen ist Vorfreude auf sich selbst.* Peter Sloterdijk”

Nuclear physics is the most violent part of physics. But despite this bad image,

uclear physics has also something to offer that is deeply fascinating: exploring

Ref. 152 uclei, we can understand the Sun, the stars and the early universe.

Nuclei consist of protons and neutrons. Since protons are positively charged, they repel

each other. Inside nuclei, protons must be bound by a force strong enough to keep

them together against their electromagnetic repulsion. This is the strong nuclear interaction;

it is needed to avoid that nuclei explode. The strong nuclear interaction is the

strongest of teh four interactions; nevertheless, we do not experience it in everyday life,

because its range is limited to distances of a few femtometres, or a few diameters of a

proton. Despite this limitation, the strong interaction tells a good story about the flesh

and blood we are made of.

The Sun

The Sun emits 385 YWof light.Where does this energy come from? If it came by burning

coal, the Sun would stop burning after a few thousands of years. When radioactivity

was discovered, researchers tested the possibility that this process was at the heart of the

Sun’s shining. However, even though radioactivity – or the process of fission that was

discovered later – can produce more energy than chemical burning, the composition of

the Sun –mostly hydrogen and helium– makes this impossible.The origin of the energy

Ref. 153 in the Sun was settled in 1939 by Hans Bethe: the Sun burns by hydrogen fusion. Fusion

is the composition of a large nucleus from smaller ones. In the Sun, the fusion reaction

4 1H → 4He + 2 e+ + 2

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