subelectron

A subelectron is a hypothetical particle that would have a charge less than the elementary charge, the magnitude of the charge of an electron. The concept of the subelectron arose in attempts to explain observations in early 20th-century physics that seemed to suggest fractional charges. While the electron itself is considered a fundamental particle with a quantized charge, some experimental results at the time were difficult to reconcile with this idea without invoking fractional charge carriers.

The most prominent historical example related to subelectrons was Robert Millikan's oil-drop experiment. Millikan's meticulous measurements of the charge on oil droplets showed that these charges were always integer multiples of a fundamental unit. This fundamental unit was later identified as the charge of the electron. However, in the early stages of interpreting such experiments, before the electron's fundamental nature was fully established, the possibility of sub-units of charge was considered.

The discovery of quarks in the latter half of the 20th century provided a resolution to the apparent puzzle of fractional charges. Quarks are fundamental constituents of protons and neutrons and possess fractional electric charges (either +2/3e or -1/3e, where 'e' is the elementary charge). However, quarks are never observed in isolation; they are always confined within composite particles (hadrons) such that the overall charge of the hadron is an integer multiple of the elementary charge. Therefore, the idea of a free-flying subelectron with a charge like -1/3e has been superseded by the quark model. Today, the subelectron is largely considered a historical concept, a stepping stone in the development of our understanding of electric charge.