Newton's Gravity
Newton wrote down his law of gravity for point particles.
It was not a trivial job for him to extend his law to particles
with nonzero size.
In 1905, Einstein formulated his special relativity for point particles.
How about rigid bodies like billiard balls or potatoes? We do not
worry about this question because of the emergence of quantum mechanics
where particles are either wave packets or standing waves. Do we then
understand Einstein's Lorentz covariance of those waves in quantum
mechanics?
Portraits of Newton are readily available, but have you seen this
version?
