I'm wondering how it has been determined that the electron is really a point-like particle. Searching for this topic, I came across a post by humanino, saying that one way we know this is that observations of the electron's "form factor" are consistent with what you'd see for a pointlike particle. I've never heard of form factors before. I googled the term and couldn't find any basic explanation of it. Could anyone help me to understand- 1. what a form factor is 2. In general, how we know that the electron is pointlike In particular, suppose I wanted to believe that instead of being a fundamentally pointlike thing whose position was often indefinite, the particle was always a continuously distributed entity that sometimes became localized into very narrow regions. what would be wrong with such an idea?