It still makes me sad that physics doesn't think about things in the simpler way that Feynman presented.
Two names for the same thing are redundant, so physicists decided to make a meaningful distinction:
By convention, 'mass' denotes the invariant but not conserved scalar quantity (rest mass/energy), whereas 'energy' denotes the non-invariant but conserved quantity, the time component of energy-momentum (total mass/energy).
Two names for the same thing are redundant, so physicists decided to make a meaningful distinction:
By convention, 'mass' denotes the invariant but not conserved scalar quantity (rest mass/energy), whereas 'energy' denotes the non-invariant but conserved quantity, the time component of energy-momentum (total mass/energy).