In Einstein’s General Theory of Relativity, space and time are unified in a single entity called spacetime. This is the “stage” in which the laws of physics operate.
In Einstein’s theory, the presence of mass and energy warps spacetime, and it is this curvature that affects objects in the way we perceive as gravity. The basic idea is that while we see objects accelerating towards a mass by the effect of a force, in reality is just the object attempting to follow a straight line in this four-dimensional warped space described by General Relativity.
In other words, things fall because they are following a straight line in spacetime.
In usual illustrations, the bending of space is represented as a flat rubber-sheet with masses pressing down on it. This has always bugged me, as it didn’t really represent the nature of 3D space being curved, and it never really addressed the fact that time is also distorted near masses.
This is my first attempt at a better depiction of the effects of General Relativity. Here, we see a 3x3x3 section of an imaginary spatial grid (that extends throughout all of space) being distorted by the presence of a mass. At the intersections of the grid lines there are clocks that show the rate of passage of time at each point in space, relative to a far away observer.
Notice how the clocks near the mass measure time at a slower pace than the clocks further away from the mass.
The distortion of spacetime is real, and can and has been measured experimentally several times. Modern telecommunication satellites and GPS systems all make use of the predictions of General Relativity in order to function.
While bizarre and complex, General Relativity has stood the test of time, and is one of the most well-tested and successful scientific theories ever conceived.