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In The Character of Physical Law, Feynman presents a brief proof that charge conservation must be local. I had some confusion over local vs. global conservation, but thought I understood after reading the discussion in this question.

Later on in the same lecture/chapter, Feynman says

A mass, in a box, cannot just disappear from one position and move over to another position all by itself. That is nothing to do with conservation of the mass; you still have the mass, just moved from one place to another. Charge could do this, but not a mass. [emphasis mine]

Video of the same is here.

It seems to me like Feynman is contradicting what he just proved and saying charge in fact can disappear and reappear without moving through the space in between, indicating I have some misunderstanding.

What is Feynman saying charge could do that mass cannot?

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andars
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1 Answers1

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Good question. Here, Richard Feynman is contrasting the properties of charge and mass. A charge can move down a wire or something without affecting the angular momentum. A mass cannot move like that without affecting the angular momentum. So he's saying "mass" has a different kind of physical property than "charge".

If you watch the succeeding part of the video and think about the point he's trying to make, it makes more sense.

Suzu Hirose
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