# Is there any idea why the electric charges of electron and muon are equal?

Is there any idea explaining why the electric charges of electron and muon are equal?

Edit:

The total charge of a particle is proportional to the integral of its own electric field flow through the sphere of a big radius surrounding the particle at rest.

The free Dirac equation describes charged fermion. It contains the mass term $m$. If $m$ tends to zero, Dirac equation tends to the pair of Weil equations that describe electrically neutral particles. Does it mean that charge somehow depends on mass? If yes, why do the electron and muon (both described by Dirac equation, but with different mass terms) have the same electric charges?

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Is it possible to rephrase the question(v1) in such a way that it does not overlap with this question physics.stackexchange.com/q/4238/2451 ? –  Qmechanic Feb 1 '12 at 16:52
Thanks, I didn't see that question. Give me some time to think about rephrasing/closing the question. –  Murod Abdukhakimov Feb 1 '12 at 17:08
It's worth googling for "who ordered that" (include the quotation marks as you want to search the phrase). –  dmckee Feb 1 '12 at 18:17

How do we know that there exists such a particle as the muon?

From observing its decay into an electron plus two other neutral particles, which are an antineutrino electron and a neutrino muon.

In this last sentence there are three conservation laws:

1) conservation of charge ensures that the muon has the same charge as the electron

2) lepton number conservation ensures that the number of particles with muon leptonic number and the number of particles with electron leptonic number are conserved.

These are observations, the accumulation of which together with a large number of other observations allows us to build up the standard model 0f particle physics. The Standard Model encapsulates our observations/data.

The short answer to the question is: because that is what has been observed.

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It is amusing that there exist people who think they are interested in physics and cannot accept an experimental fact, down voting this answer. They need convoluted theoretical arguments which in the end of course end up on the experimental fact. Data trumps theory every single time. Without data theory is science fiction. –  anna v Mar 24 '12 at 4:46
Of course you are right, and not my downvote, I think it's an ok answer, but the question seems to be confused about the massless limit of the Dirac equation, not about particle properties. –  Ron Maimon Mar 24 '12 at 7:28