Structure of Matter
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An Unanswered Question

 
 

By the 1930s, the view of atoms had reached a critical stage. Atoms were understood to be made of a nucleus composed of protons and neutrons (James Chadwick, The Nobel Prize in Physics 1935) and an outer cloud of electrons (Joseph John Thomson, The Nobel Prize in Physics 1906). These three particles were thought to be the fundamental constituents of all matter.

But the question remained: How does a nucleus hold together when all of the protons inside are repelling each other? What is keeping the nucleus intact?

This led to experiments with particle accelerators to study neutron and proton interactions. However, in addition to finding an answer, these experiments found many other types of particles. This raised a host of new questions that eventually led to an entirely new understanding of the fundamental structure of the nucleus.