I was wondering what causes the charge in the subatomic particles.
Current theory has no explanation for the charges. String theory may give an answer when it ever gets worked out fully.
To add to what mathman has explained, charge is basically the coupling constant of electrical interactions. A coupling constant expresses the strength of an interaction.
The electrical coupling constant is actually called the "fine structure constant" as is shown in the website. The e is present in it's definition and in high energy physics, the c is equal to 1 (God's units), so only the e "actually matters" in the definition.
There is a principle in Quantum Mechanics called "Local Gauge Invariance".
Simply put, it means the phase of the wave function is arbitrary at any point in space. It can be shown that LGI can only hold if all particles have a charge (either EM, strong, or weak). The LGI principle, for the first time, answers your profound question. As with any answer, it raises its own questions.
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