system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How is gravity not faster than the speed of light?

If i drop a ball on the ground, every atom that composes the earth is instantly impacting the strength which with the ball is pulled to the earths mass.

A relationship between a single atom on the other side of the planet and the ball dropped is formed as if in an instant.

If you have spiral arms of a galaxy, the strength which with the arm is pulled to the center is a summary of every atom of that galaxy.

I could go on for hours talking about these absurd effects at a distances far larger than light can cover but somehow is instantly calculated by mass and gravity.

How is gravity not faster than the speed of light?

EDIT: Thanks for the responses everyone, this was awesome.
gpt
This is a very perceptive question.

You have touched on one of the fundamental flaws of Newtonian gravity: the fact that it is "non-local".

We know that the speed of light must be constant in all frames of reference, and yet Newton's formulation of gravity requires that gravitating bodies *instantaneously* know where everything else is, as you mention in your question.

So one of the motivators of general relativity was to develop a *local* theory; i.e. one in which the effects of gravity on a body are simply the results of some feature of its IMMEDIATE surroundings.

And so we describe gravity as the effect of *curved* spacetime.  We imagine that all masses cause a curvature in spacetime around them, and this curvature distorts the paths of other bodies in the vicinity.

So the "gravity" felt by a body is simply the effect of the curvature of spacetime in its immediate region.  This removes the issues of non-locality since no information needs to be transmitted at higher-than-light speeds.

I hope this explanation helps, feel free to ask follow-up questions.

Edit: I've mentioned this a little lower down in the comment chain, but it is an important point which belongs here too: *changes* to curvature propagate at the speed of light.  i.e. if, through some truly epic disaster, the sun suddenly popped out of existence, we would not encounter the effects until about 8 minutes later.  This is due to the fact that *information* cannot travel faster than light (in a vacuum).