The Common Visualisation Of General Relativity

Robinson (2005: 75, 77):

Gravity would no longer be an interaction of bodies through a law of forces; it would be a field effect that emerged from the way in which mass curved space. When a marble is propelled across a flat, smooth trampoline on which sits a large and heavy ball, the marble follows a curved path around the depression caused by the ball (see Fig. 5).

In the Newtonian view a gravitational force emanates from the ball and somehow compels the marble to move in a curve. But according to general relativity it is the curvature of space — or rather space-time — that is responsible; there is no mysterious force. Matter tells space how to curve; space tells matter how to move — this is a grossly simplified summary of Einstein's general theory of relativity.

Blogger Comments:

If, according to Einstein's theory of General Relativity, gravity is the relative contraction of space intervals and expansion of time intervals, with increasing proximity to a centre of mass, then this very common representation of gravity is inconsistent with the theory, and thus a source of confusion. 

Specifically, the expansion of time intervals is not addressed, and space intervals are not shown as contracting with proximity to the ball, but rather as slightly expanding, as two dimensions of space are curved in a way to cause the curved trajectory of the marble.

The curved trajectory of the marble, however, actually corresponds to the geodesic that arises from space intervals being contracted in the direction of the ball.