Hypothetical particles believed to exist at the Planck scale (right) are about a billion billion times heavier than the known particles (left). The tendency of particle masses to equalize in calculations makes this a puzzling hierarchy.
Supersymmetry theory posits the existence of a twin for each of the known particles, counteracting the particles’ tendency to escalate to the Planck scale. As of yet, no supersymmetric twins have turned up at the Large Hadron Collider.
A new idea holds that particles attain their masses as a result of scale-symmetry breaking: The underlying theory of nature lacks any concept of mass, and independent quantum effects cause mass to arise at two widely separated scales.