| Themes > Science > Physics > Elementary particle physics > Elementary particle physics Today > String Theory and the Unification of Forces > The Four Forces |
Experimentally it is known that there are just four basic forces in nature. Two of them are very familiar: the electromagnetic force, and the gravitational force. The other two are invisible unless we probe deep inside the nucleus of the atom. They are called ``nuclear forces'' and come in two varieties, the ``weak'' and the ``strong'' force. The weak nuclear force is responsible for radioactive decay, while the strong force binds protons and neutrons together to make up the nucleus. |
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