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).

More Stories from Science News on Particle Physics

From the Nature Index

Paid Content