If this is true, however, then the ball and the bullet which start off on the same path should logically continue on the same path. The objects themselves are just moving in straight lines. This might not seem strange at first, but under Einstein's reconception of gravity, it's a major problem! Einstein's idea (discussed further on our relativity page) was that there is no such thing as a 'force' of gravity which pulls things to the Earth rather, the curved paths that falling objects appear to take are an illusion brought on by our inability to perceive the underlying curvature of the space we live in.

However, as we know, their paths quickly diverge - the bullet will travel much farther before hitting the ground than the ball does. they both start off moving horizontally away from the person's head). The ball and the bullet both start off along the same path in space (i.e. This is a great question which goes to the heart of why Einstein said gravity is the curvature of space-time, rather than just the curvature of space.Ĭonsider the diagram below, which shows the situation you describe in your question. If gravity can be defined as the curvature of space rather than a force of attraction, why does not a bullet shot out of a gun, say perpendicular to the Earth's crust, and a ball thrown by me on the same trajectory (but obviously at a much slower speed) follow the same curve? If gravity is actually curved space and if falling objects are simply following the natural curves of space why does each object have its own curve?

Gravity as curved space activity