# Beta- decay

by Edi
Tags: beta, decay
 Mentor P: 11,745 The W- is a virtual particle in this case. Virtual particles are "off the mass shell," that is, they don't satisfy the mass-energy-momentum relationship for real particles, $E^2 = (pc)^2 + (mc^2)^2$. Alternatively, people sometimes say that virtual particles can very briefly violate conservation of energy by "hiding" behind the uncertainty principle.