# Charge is Invariant

1. Aug 28, 2006

### Swapnil

Why is charge an invariant quantity? My professor once said that that is an experimental fact. I believe him. But is there an "intuitive" reason for why a charge should be an invariant quanity?

2. Aug 29, 2006

### pmb_phy

No, there is no intuitive reason that I know of. The conservation of charge is simply taken to be an axiom in physics.

Pete

3. Aug 29, 2006

### HallsofIvy

Staff Emeritus
I dislike that wording. There are no "axioms" in physics. There is only "experimental evidence".

4. Aug 29, 2006

### Meir Achuz

"invariant" here could be ambiguous. If you mean "conserved", that is an experimental question with overwhelming experimental verification.
More likely, it means invariant with respect to a Lorentz transformation. This can be proven mathematiclly, starting with the continuity equation
(which follows from charge conservtion).
The proof is a bit tricky.

5. Sep 10, 2006

### leright

There have been many axioms or assumptions (educated guesses in physics). For instance, Ben Franklin and his GUESS that it was positive charge that was free flowing in the wire. Positive charges DO flow in the direction opposite the electrons, but Franklin believed it was the positive charges in the wire that were the physical objects moving, which is the opposite of what we know now.

Also, the idea that the speed of light was constant was in fact an axiom (Einstein calls it a POSTULATE) in his original paper. There was no experimental evidence for this. Just as Newton assumed all of his laws are the same in all inertial frames, Einstein assumed ALL laws of physics, beyond newton's, were the same.

Last edited: Sep 10, 2006