# Some Relativity Questions

*Most recent answer: 05/29/2017*

- Ian Lee (age 17)

San Diego, CA USA

I'll try to answer those, not in order, but you may find some of the answers unsatisfactory.

"...why objects experiencing stronger gravitational pull experience larger time dilation?" Objects don't actually "experience" gravity. There's no feeling or other local change due to a uniform gravitational field, no matter how strong. The time dilation factor between two regions depends on which one is "down" in the gravitational field, and how far down. You could have two planets so that somebody in between two would be at a zero-field point (in a conventional center-of-mass frame) yet their clocks would run slower than those of somebody farther away who was uphill but still in a field.

For your first questions, yes, the geodesic (what passes for straight in this context) paths through spacetime of two objects, say you and the earth, can start off parallel and then approach each other at accelerating rates. That is, as you say, because their mass causes spacetime to be warped. Maybe this picture will help. Imagine a space that's the surface of a sphere, like the surface of the Earth but not imbedded in some bigger space. You and a friend start north from the equator, initially at a fixed distance, say 3 feet. Neither one of you bends or swerves but just continues on as straight a path as possible. You'll start getting closer and, when you reach the north pole, collide. Neither one of you will feel a sideways force at any time before the collision. Yet keeping track of your distance, it looks like one or both of you must have accelerated sideways. To keep from colliding, you have to push apart and experience sideways forces. I think that captures the basic idea behind what you're wondering about.

Mike W.

*(published on 05/29/2017)*