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Is there anything smaller than a quark? © Getty Images

What holds together the protons and neutrons in an atom’s nucleus?

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The rule opposites attract and likes repel has to be overcome if protons and neutrons are to stay together inside a nucleus. This is where quarks can help.

Asked by: David Kelly, Manchester

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All protons are positively charged, and as a result repel each other. So the fact that atoms even exist points to a force able to overcome this repulsion.

Called the strong interaction, its origins lie in the particles lurking inside both protons and neutrons, called quarks. These possess a weird form of charge, whimsically termed ‘colour’, which glues them together inside their host particles – and also seeps out to bind the protons and neutrons together, too.

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Authors

Robert is a science writer and visiting professor of science at Aston University.

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