# How exactly can we describe the normal force on a static person standing on earth's surface using general theory of relativity?

For planetary motion I can understand that the planets move along the geodesics e.g. the warped space-time geometry. Imagine that the moon gets suddenly stopped by some external force and comes to rest momentarily, which force will bring it to motion towards earth. And how can we describe "Normal force" as mentioned in the subject.

Please excuse me for my ignorance in advance but an excessively mathematical explanation would be very difficult for me to understand.

• I'm not sure what you're asking here. It seems you're worried about the normal force, the one that impedes one object to enter another, and in the gravitational case maintains a person standing on the Earth. The normal force is just a by-product of quantum mechanical interactions and has nothing to do with general relativity. If you're concerned with how to describe near-earth gravity (as a constant force) in general relativity then you can do no better than Feynman's lecture 42 of volume 2, freely available here feynmanlectures.caltech.edu/II_42.html Jun 6, 2014 at 19:00
• @cesaruliana, You've got me right, I can try to clarify my doubt again - "according to Einstein gravity is not a force but an illusion e.g. as moon moves around earth in a geodesic formed by warping of spacetime by mass of earth but not by the so called illusionary gravitational pull. So exactly how can we describe the normal force as I mentioned?", thanks for the link I will go through it. Jun 12, 2014 at 7:56
• I was very much looking for the non Newtonian explanation of normal force which is in conformance with the Einstein's ideas about gravity. Jun 12, 2014 at 8:05
• @ Yogesh, the normal force is non-gravitational and therefore does not have a geometrical description in general relativity, in the same way as electromagnetism does not. In fact from the point of view of GR a person standing on the surface of Earth is not in equilibrium with respect to forces, there is only the normal force pointing against the ground. What happens is that in GR free-fall is inertial behavior, therefore in order to stand still one must be in non-inertial motion, namely subject to net forces, in this case the normal. Is that what you're asking? Jun 12, 2014 at 15:32