The equivalence suggested to Einstein that the path an object follows is a property of space itself, rather than having anything to do with the specific properties of the object.

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We know that in the absence of any forces, objects follow straight lines, and

we also know that straight lines are the shortest possible paths……

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Perhaps gravity is a manifestation of objects in free fall following the shortest

possible paths, known as geodesics, in curved spacetimes

It is difficult to visualize curved spacetimes, but the surface of a sphere is a simple curved space. Geodesics are great circles that pass through both poles. We see that they can pull apart and then meet up again….

## David Kastor

COSMOS to HUMANITY, Spring 2008

Lecture 2 , slide 4