To give you an idea of the scope of the Einstein revolution, consider the fact that before Albert Einstein (1879-1955), our understanding of the world had these features:

1. No formal theory of relative motion existed, although an addition-of-velocity rule existed.
2. Physicists believed with Newton that absolute motion exists—that a body’s motion can be detected without reference to any other body.
3. Physicists thought that a fixed ether permeates the universe.
4. Space was viewed merely as an empty container.
5. Physicists could not explain the photoelectric effect or Brownian motion.
6. Several noted physicists rejected the notion of atoms.
7. The separate conservation laws for mass and energy largely were on equal footing.
8. Everyone believed that time is absolute. That is, none realized that motion affects time judgments.
9. None realized that nature has a speed limit (the speed of light), which no material body can attain.
10. None realized that the speed of light is a constant and is independent of the motion of the light source.
11. None realized that all laws of nature are the same in any 2 systems that are moving relative to each other.
12. Everyone believed with Newton that gravity is a force (of attraction).
13. None realized that gravity is equivalent to acceleration (Einstein’s equivalence principle).
14. None realized that energy (E) and mass (m) are related thusly: E = mc², where c is the speed of light.

Items 10 and 11 (minus each one’s first 3 words) are the basis of the special theory of relativity, which considers rectilinear motion sans acceleration. It debuted in 1905. In 1915, Einstein completed the general theory of relativity, which considers all forms of motion. It gave us a new theory of gravity.