Charged and uncharged particles respond differently to an electric field, allowing for a clear distinction.
Gravity is not a force like electromagnetism, but a feature of space-time itself.
Einstein proposed that gravity could be a result of curved space-time.
Einstein learned non-Euclidean geometry from mathematician Marcel Grossman, which allowed him to develop his theory of general relativity.
My little pandemic-lockdown contribution to the world was a series of videos called The Biggest Ideas in the Universe. The idea was to explain physics in a pedagogical way, concentrating on established ideas rather than speculations, with the twist that I tried to include and explain any equations that seemed useful, even though no prior mathematical knowledge was presumed. I’m in the process of writing a series of three books inspired by those videos, and the first one is coming out now: The Biggest Ideas In The Universe: Space, Time, and Motion. For this solo episode I go through one of the highlights from the book: explaining the mathematical and physical basis of Einstein’s equation of general relativity, relating mass and energy to the curvature of spacetime. Hope it works!