Is there anything smaller than a quark? © Getty Images

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

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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