# 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 non-zero 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?

- Click here for more about the Internal Space and Time.
- Portraits of Newton are readily available, but have you seen this version?