By Rafi Letzter
No one really knows what happens inside an atom. But two competing groups of scientists think they’ve figured it out. And both are racing to prove that their own vision is correct.
Here’s what we know for sure: Electrons whiz around “orbitals” in an atom’s outer shell. Then there’s a whole lot of empty space. And then, right in the center of that space, there’s a tiny nucleus — a dense knot of protons and neutrons that give the atom most of its mass. Those protons and neutrons cluster together, bound by what’s called the strong force. And the numbers of those protons and neutrons determine whether the atom is iron or oxygen or xenon, and whether it’s radioactive or stable.
Still, no one knows how those protons and neutrons (together known as nucleons) behave inside an atom. Outside an atom, protons and neutrons have definite sizes and shapes. Each of them is made up of three smaller particles called quarks, and the interactions between those quarks are so intense that no external force should be able to deform them, not even the powerful forces between particles in a nucleus. But for decades, researchers have known that the theory is in some way wrong. Experiments have shown that, inside a nucleus, protons and neutrons appear much larger than they should be. Physicists have developed two competing theories that try to explain that weird mismatch, and the proponents of each are quite certain the other is incorrect. Both camps agree, however, that whatever the correct answer is, it must come from a field beyond their own.
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