The speed of light in a vacuum is the same for all observers, regardless of the motion of the light source.The laws of physics are invariant (i.e., identical) in all inertial systems (i.e., non-accelerating frames of reference).However, in 1905, Einstein based a work on special relativity on two postulates: Prior to his pioneering work, scientists had two separate theories to explain physical phenomena: Isaac Newton's laws of physics described the motion of massive objects, while James Clerk Maxwell's electromagnetic models explained the properties of light. The physicist Albert Einstein helped develop the idea of spacetime as part of his theory of relativity. Until the 20th century, it was assumed that the three-dimensional geometry of the universe (its spatial expression in terms of coordinates, distances, and directions) was independent of one-dimensional time. Spacetime diagrams can be used to visualize relativistic effects, such as why different observers perceive differently where and when events occur. In physics, spacetime is a mathematical model that combines the three dimensions of space and one dimension of time into a single four-dimensional manifold.

Curved space time