Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

This question already has an answer here:

Isn't mass a fixed and an intrinsic property of a particle? How can we talk about eigenstates of the mass in the context of neutrinos?

share|cite|improve this question

marked as duplicate by DavePhD, Brandon Enright, John Rennie, Qmechanic May 8 '14 at 10:52

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

Mass is not fixed... considering accelerators and E=mc^2. Energy is an eigenvalue, so the same applies to mass. – somewherehere May 2 '14 at 21:45
Related: – Alfred Centauri May 2 '14 at 22:31
@cppinitiator The "mass of a particle" means (in modern parlance) the Lorentz invariant mass (you may know it as the "rest mass"). There is nothing wrong with the idea of relativistic mass as such, but significant parts of physics have deprecated the term. Particle physics is one of those areas. – dmckee May 3 '14 at 0:51