How did Einstein reshape our world view?

By the early 1900s, scientists had established that the speed of light was a constant, which challenged the classical theory that velocity is additive: A swimmer moving at one mile an hour in a two mile an hour current travels three miles an hour, but light beamed from a moving train still travels 186,000 miles per second. Albert Einstein developed equations showing that space and time, the other variables involved in velocity, change as object approach the speed of light. Astronomical observations eventually confirmed this, as did experiments on airplanes that showed time does slow as speed increases.

Einstein's special and general theories of relatively unified are three dimensions of space with fourth dimension of time; explained in interchangeability of mass and energy through the famous equation E=mc2; and recast gravity as a force that acts by bending space. That effect is only across massive distances and at high speeds, but understanding it helped unlock some very powerful forces, such as nuclear energy.