History of the Universe

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Nucleosynthesis 3 to 20 minutes

Nucleosynthesis is the process of creating a nucleus, that is, an object which (as we will see later in this story) can become the center of an atom.

Nucleosynthesis occurred during the Photon Epoch. It started about 3 minutes and ended about 20 minutes after the creation.

The process involves the fusing together of two or more particles and so it is an example of nuclear fusion.

Nuclear Fusion

Nuclear fusion is the process of fusing together (or combining) two nuclear particles. Nuclear fusion was the process which powered nucleosynthesis during the Photon Epoch. It also occurs inside stars, and is the main way in which stars convert matter energy into light.

Nuclear fusion occurs in hydrogen bombs. Much work is currently going on to try to make nuclear fusion happen on Earth in a controlled way. Scientists believe that a great deal of energy will be released in this way with very little pollution.

ITER, currently being contructed in the South of France, is a large-scale international trial that aims to prove it is possible to produce commercial amounts of energy from nuclear fusion. It is due to start working in November 2019. The scientists say that "By the last quarter of this century, if ITER and DEMO are successful, our world will enter the Age of Fusion - an age when humanity covers a significant part of its energy needs with an inexhaustible, environmentally benign, and universally available resource."

Proton fusion

One of the most important fusions is described here. It occurred both in the young Universe and still happens today inside stars. It is the main process which produces sunlight. Notice that several important details have been omitted from our explanation to keep it simple.

Simplified diagram of proton fusion

Proton fusion starts when four protons are pressed so close together that the quarks inside them begin to be attracted and the protons stick together. The force of repulsion between the four positive electric charges is so strong that two of the charges are ejected from the group. They materialize as two small particles called positrons. These are the antimatter equivalent of the electron. They very soon met some normal electrons and immediate annihilated with them, all their energy  being converted into radiation.

Helium Nucleus

Meanwhile the two protons which had lost their charge had been converted into neutrons. The original four protons now consisted of two protons and two neutrons. This group of particles stuck together very strongly and produced a single particle called a helium nucleus. These particles are also sometimes called alpha particles.

End of nucleosynthesis

About 20 minutes after the creation, the expansion of the Universe had slowed the free protons so much that they did not have enough energy to overcome their mutual force of electrical repulsion and the period of nucleosynthesis came to an end. From now on the Universe consisted of protons, electrons, helium nuclei (the plural of nucleus) and radiation.

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History of the Universe eBook
History of the Universe eBook
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Written by Wyken Seagrave
Copyright © 2017 Penny Press Ltd