The Mysteries of the World’s Tiniest Bits of Matter

Physicists have known for decades that particles called gluons keep protons and neutrons intact—and thereby hold the universe together. Yet the details of how gluons function remain surprisingly mysterious

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The ancient Greeks believed atoms were the smallest bits of matter in the universe. Then scientists in the 20th century split the atom, yielding tinier ingredients: protons, neutrons and electrons. Protons and neutrons, in turn, were shown to consist of smaller particles called quarks, bound together by “sticky” particles, the appropriately named gluons. These particles, we now know, are truly fundamental, but even this picture turns out to be incomplete.

Experimental methods for peering inside protons and neutrons reveal a full-fledged symphonic orchestra within. These particles each consist of three quarks and varying numbers of gluons, along with what are called sea quarks—pairs of quarks accompanied by their antimatter partners, antiquarks—which appear and disappear continuously. And protons and neutrons are not the only particles made of quarks found in the universe. Accelerator experiments in the past half a century have created a host of other particles containing quarks and antiquarks, which, together with protons and neutrons, are called hadrons.

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