Here's why we believe this:
* No evidence of internal structure: Numerous experiments have been conducted to probe the internal structure of electrons, using high-energy collisions and other methods. None of these experiments have found any evidence of substructure within an electron.
* Point-like nature: Electrons behave as point-like particles, meaning they have no measurable size or internal structure.
* Standard Model: The Standard Model of particle physics, which successfully describes the fundamental building blocks of matter and their interactions, classifies electrons as fundamental particles.
However, it's important to remember that our understanding of physics is constantly evolving. It's possible that future discoveries could reveal that electrons are actually composed of more fundamental particles, but currently, there's no evidence to suggest this.
