50 years ago, physicists got a whiff of what glues together protons

Excerpt from the September 16, 1972 issue of Science News

an illustration of the internal structure of a proton

In this illustration of a proton’s internal structure, quarks (represented by the letters U and D) are held together by the strong nuclear force (helices), which is imparted by particles called gluons.

Mark Garlick/Science Photo Library/Getty Images Plus

cover of the September 16, 1972 issue of Science News

What holds the proton togetherScience News, September 16, 1972

An experiment … at the CERN Laboratory in Geneva … gives an important clue to structural arrangements deep within the proton…. The result hints at the existence of a new and very strong fundamental interaction — the process that holds [quarks] together inside the protons.… A number of theorists have speculated about its nature and have even proposed an intermediate particle for it called a gluon.


Physicists finally found evidence for gluons in 1979, in the aftermath of electron-positron collisions at a German particle accelerator (SN: 4/21/79, p. 262). Gluons bind quarks inside protons via the strong force — the most powerful force in nature. Recent investigations of gluons’ role inside the proton suggest the particles’ energy makes up about 36 percent of the proton’s mass (SN: 12/22/18 & 1/5/19, p. 8). Future particle accelerators could gauge gluons’ contribution to the proton’s internal pressure, which averages a million trillion trillion times the strength of Earth’s atmospheric pressure (SN: 6/9/18, p. 10).

Maria Temming

Previously the staff writer for physical sciences at Science News, Maria Temming is the assistant editor at Science News Explores. She has bachelor's degrees in physics and English, and a master's in science writing.

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