Proton and Electron Charge Signs

Why does a proton have a "positive" charge and an electron have a "negative" charge? Why should charge exist?
- james (age 16)

The convention of which sign of charge is positive and which is negative is purely arbitrary. In fact, it was Benjamin Franklin who proposed in the mid 1700’s that charge is conserved -- that total charge remains the same even though positive charges can be separated from negative ones. He proposed that electric charge was some kind of fluid, and that objects that gained fluid have positive charge and object that lost it gained a negative charge. He based his convention on which signs of charges were deposited by either glass or amber on an object that was rubbed on them. We’ve lived with his convention ever since.

Other kinds of charge exist! The electromagnetic force is just one of several that particles interact with in nature. The weak nuclear force introduces other kinds of charge (often called "hypercharge" or just weak charge) which are actually related in a very wonderful way to the electrical charges; the weak nuclear force and the electromagnetic force are described together in a beautiful model which describes how at very high energies they are one and the same kind of interaction.

The strong nuclear force (for which the 2004 Physics Nobel Prize was awarded to Gross, Politzer and Wilczek just a couple of days before I am writing this), involves additional kinds of charge, which interact with the carriers of the strong nuclear force, called gluons. These are a lot like photons (which interact with anything with electrical charge), except that the gluons themselves carry strong-force charge and therefore interact with each other, making a gluey, sticky mess.

We do not know why charge should exist. (I guess if it didn’t, there wouldn’t be interactions, and we wouldn’t exist if the elementary building blocks of matter didn’t interact with each other).

Tom

P.S. Some of those other kinds of charge cannot be expressed as simple positive or negative numbers at all, but require more complicated mathematical representation. I think we have an old answer on that topic. / Mike W

(published on 10/22/2007)