I don’t know where you got that idea.
Your logic assumes there’s only one light source, no atmospheric dispersion, light is a particle, and everything around the object is non-reflective. And it’s moved to a white background, something we know reflects light.
salarua@sopuli.xyz 14 hours ago
The reason the shadow is gray is because light is bouncing off the other surfaces in the environment. The shadowed area isn’t receiving direct light, but it is receiving reflected indirect light.