According to quantum mechanics, the distance range of a force is inversely proportional to the mass of its force carriers. The electromagnetic force, for example, has an infinite range; a free electron on Earth will, in principle, experience a slight repulsion from an electron on the other side of the moon. Photons, which carry the force between the electrons, are therefore massless. In contrast to electromagnetism, the range of the strong force does not extend outside the nuclei of atoms. This fact would imply that gluons are very massive. Gluons, however, appear to be massless.

The strong force is also peculiar in that it seems to pull on quarks more strongly the farther away they get. In contrast, the electromagnetic force between two magnets is strongest when they are close and weaker when they are apart.

This force between quarks corresponds to a weight of 16 metric tons at separations that are roughly the size of a proton. But what happens if an outside force pushes against the strong force’s pull? The string snaps.