Why are electrons taken implicitly to be the elementary charge? It would save a lot of fractions in particle physics problems.

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    $\begingroup$ It's an accident of history. If we'd discovered quarks before electrons the electron charge would be -3. The convention is too well entrenched to be worth the pain of changing now. $\endgroup$ – John Rennie Sep 9 '14 at 5:16
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    $\begingroup$ Or it might even be +3 :) $\endgroup$ – Ruslan Sep 9 '14 at 6:01
  • $\begingroup$ @JohnRennie I disagree: When it's wrong, it's wrong. It's arbitrary anyway - you could just use a different unit, say "q charge", ie an electron has a q charge of -3. $\endgroup$ – Bohemian May 11 '15 at 1:09

It's a matter of history. When George Stoney developed Stoney units in 1881, or when Robert Millikan performed the oil drop experiment in 1909, it wasn't yet known that it was possible for anything to have a charge smaller in magnitude than the charge of an electron. By the time the quark model was proposed, in 1964, the use of the "elementary charge" being taken to be the magnitude of the charge of an electron was already firmly established. Changing the definition of an "elementary charge" unit due to the quark having been discovered would have led to too much confusion.

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  • $\begingroup$ Not to mention, it'd be a bit cocky to think that 1/3 of the charge of an electron is the ultimate elementary electric charge. I don't know how sure we are of that today, or even if we're sure it is not, but we were much less sure in the '60s when it would have been relevant. $\endgroup$ – hyde Sep 9 '14 at 11:16
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    $\begingroup$ Furthermore, only particle phyisists care about quark charges. All solid state and applied physicists, chemists, electrical engineers and so on only ever deal with multiples of the electron's charge. So besides the historical issue, there is a practical side to it, too. $\endgroup$ – Neuneck Sep 9 '14 at 12:04

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