What is the inside of an electron like?

The electron is one of the oldest-known fundamental particles, and a lot has been learned about it in the last 100 years. We know its mass (9.1095 x 10-28 grams), its charge (4.8032 x 10-10 ESU) and its spin (1/2 units). From relativity experiments and the way its electromagnetic field behaves, we also know that it gains mass as it is accelerated in such a way that it cannot be a small sphere of matter with electrical charge on its surface. It is instead a truly point-like object whose 'size' is smaller than 10-20 inches. Also, its relativistic mass increase is a result of its electromagnetic field energy, not that its 'rest-mass' is increasing. Rest-mass is a measure of a body's inertia when it is not moving in the reference frame of the experiment, and so it is the minimum possible mass that a body can have.

Modern electroweak theory, which unifies the electromagnetic and weak-nuclear forces, says that electrons are actually have no mass at all at energies of 100 GeV or higher .At these energies, the vacuum itself takes on a different energy state and this causes the symmetry between electromagnetism and weak forces to break down. Electrons get their rest mass from the interaction of the massless electron field with the Higgs field in the vacuum. String theory says that electrons have no internal structure until you get to Planck Energies of 1019 GeV where their string-like characteristics become obvious. So, an electron is basically a 'knot' of energy in the electromagnetic field, and the field itself is produced by the emission and absorption of virtual particles from 'within' the electron itself.

This answer was updated in 2011. See my books: The Astronomy Cafe (1998) and Back to the Astronomy Cafe (2003) for more FAQs in printed form. Author: Dr. Sten Odenwald, Copyright 2011

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