In experiments where high-energy electrons occasionally scattered straight backward off protons, what did that backward scattering suggest to researchers about the structure of the proton?

1. Scattering an incoming particle straight backward requires hitting something small, dense, and hard to move, much like a ball bouncing off a wall rather than a piece of fluff. 2. This is exactly the outcome observed for electrons scattering off protons. 3. It states that this backward scattering implied a very small and very dense particle makes up the proton, taken as near direct evidence of quarks. 4. Momentum conservation is the analysis tool used to interpret these results, not something the results call into question, and this evidence points toward internal structure, not the absence of any. _Source: OpenStax College Physics (CC BY 4.0), Ch 8 "Linear Momentum and Collisions", section 8.3 Conservation of Momentum_