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Is there exactly the same number of electrons as there are protons in the universe? Is that also true of Earth at any given moment?

Eric Kvaalen
Les Essarts-le-Roi, France

In most stars, hydrogen is turning into helium, and the process starts with two protons coming together to form helium-2. This usually splits back apart very quickly, but sometimes one of the protons turns into a neutron, a neutrino and a positron (a positively charged anti-electron). The positron annihilates quickly with an electron.

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Even though protons in stars last millions or billions of years and the positrons last only a fraction of a second, there are positrons in the stars, and this means that if the star is neutral, there are more electrons than protons. Earth is constantly bombarded by cosmic rays, which are mostly made up of protons. This must give Earth a positive charge, but one that doesn’t continue to grow because it will attract electrons from the solar wind. So there may be more protons on Earth than electrons.

On the other hand, when a high-energy proton hits the air, it creates a shower of other particles, including lots of electrons and positrons. That gives an excess of electrons over protons locally. In any case, it seems certain that there isn’t the same number of protons as electrons, neither in the universe as a whole nor on Earth.

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