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Space Time Theory

Here's some basic background covering how mathematical models of space and time have evolved since ancient times, from the Pythagorean Rule to Newtonian mechanics, Special Relativity and General Relativity.

What is spacetime?

Why was Einstein's Special Theory of Relativity needed?

How does Einstein's Special Theory of Relativity work?

What is "causality" and what does it have to do with time travel?

What is gravity?

What is Einstein's General Theory of Relativity?

Observations of spacetime bending light

Flatland with gravity - how does that work? In one time and two space dimensions, the Einstein equation is almost too simple, but the results are not! See how spacetime curvature warps light cones, creates ambiguities in causal boundaries, and even allows at least a mathematical possibility for time travel.

Space / Time in 2 dimensions