The standard explanation of gravity (according to Google's dictionary) puzzles me:
Gravity is the force that attracts a body toward the center of the earth, or toward any other physical body having mass.
The whole idea of a "body" or an "object" is really just a human invention. It's a communication tool that allows us to refer to a mass of atoms. When we say "earth" we mean all the atoms in the atmosphere, on the surface, and inside the core of the planet. But from the point of view of pure physics, there is no "earth," just a collection atoms, right? Similarly, there is no "me", just a collection of atoms that are held together through chemical bonds and a semi-permeable membrane (skin).
At first I was thinking "maybe by 'body' it means a collection of atoms that are chemically bonded to each other into molecules, crystals, etc?" but then I realized the earth's gravitational field is made up of many things that aren't bonded. Like, all the water in the ocean isn't bonded to the molten iron in the earth's core, but the mass of both of them counts towards the earth's total mass, and adds to the gravitational force that earth exerts on nearby objects, like the moon.
So my question is, how does gravity really work? If it's not at the level of composite "bodies", it seems like it must be at the level of the individual atom. Here's how I'm guessing it works, but I would love to be corrected if I am wrong:
Each atom in my body is individually affected by the force of all other atoms nearby (proportional to the mass and the distance of the atom). Because there are way more atoms beneath my feet than above my head, the net effect on each atom in my body is to be pulled down towards earth. So an atom at the top of my head has slightly less gravitational force acting on it than an atom at the bottom of my shoe, because it's a tiny bit further from the most of the atoms in the earth. And the atom at the bottom of my shoe is being pulled up slightly by the atom at the top of my head, but the net effect is for it to be pulled down, because there are more atoms beneath it.
But it's not like there is a thing called "earth" that has a certain mass and thus exerts one singular gravitational force on nearby bodies like "me", right?
Is this right, or am I missing something? I am very interested in learning more about this!