Relativity
Prior to 1905 the concept of relativity was the term where we simply discussed ones experiences from your own frame of reference. The car you see stationary beside you is actually moving relative to the ground, only because you are also moving with that car.
(This is discussed here)
But then in 1905 Albert Einstein developed his special Theory of Relativity. Because of the constancy of the speed of light he determined that the relativity understanding that was known at the time had flaws. Resolving this he determined that, rather than being absolute, time, momentum and length became relative.
The following lessons explores the development of Einstein's special theory of relativity
