Theories of physics proposed by Albert Einstein in 1905 to explain the influence of he relative motion and position of an observer on his own observations.

They say, among other things, that space and time can not be considered separate ideas. The perception of space-time is different for a person standing still on earth than it is for someone moving very fast away from or toward it.

What we see is relative to (depends on) our acceleration as we move.

The General Theory of Relativity, published in 1916, defined gravitation as a function of four-dimensional space-time.