Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

When a rock falls from a ledge, why does it head to the surface and not up to where time runs faster?

If a rock, free from forces, follows a worldline of maximum aging, why would that rock approach Earth where the rate of time runs slower, and so would slow down the rocks aging? Shouldn’t the rock avoid earth?

share|cite|improve this question
Related: – Qmechanic Jun 28 '13 at 19:22
This explains it brilliantly:… – Tom Slijkerman Mar 18 '15 at 20:39

A rising trajectory is a geodesic. A falling trajectory is a geodesic. The principle of maximum aging doesn't select one geodesic over other geodesics. It tells us which world-lines are geodesics and which ones aren't. Given two spacetime events A and B, there is typically exactly one geodesic connecting them. In your example, you've only specified A, not B.

share|cite|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.