What makes gravity apply force to objects? Why does gravity not get pulled into the center of gravity itself, or scatter? I know that every physical body has some amount of gravity, that attracts other bodies. I also know that in order to make one physical body move, another physical body must apply force to it, so what is that physical body that gravity is made out of?
Also electric fields of magnets and atoms. What keeps the electrons from flying away from the nucleus? Is it same as gravity?
Is gravity our spacetime “sinking” into itself due to high amount of matter in one spot? Then what physical thing is the spacetime made out of to be affectable by matter?
I know its a lot of speculation and questions on my part, but i am fascinated by how physics does its thing.
In: 109
What is gravity made of?
Short answer: space.
Longer answer:
Well this stuff is difficult, we don’t call it rocket science for nothing. I don’t think there is any explanation a 5yo will grasp, even my own 7yo kid won’t. But we can shoot for 10yo and hope for the best?
I’m going to talk only about gravity. And I’m not really going to talk about gravity, I’m going to talk about a toy model that will sort of illustrate the basic concepts. That’s because the human brain simply can’t directly comprehend it (some claim to, but who knows if they really do). The reason we can’t should become clear. So what we’re going to do is make a toy that has some of the same features and then show how they would have counterparts here in the “real world”. Yes?
Imagine a person that is flat, and they live in a flat universe. So instead of our three dimensions of width, height and depth, they only have the first two, width and height. We’ll call them flatties. Everything we see in our universe is in our 3D space, everything in theirs is in that 2D space. So if two siblings live in that universe, then they are the same plane – you don’t have flatties above each at different depths, they’re all on the same big piece of paper.
Since flatties evolved in a universe with only two dimensions, their brains can only understand two dimensions. It doesn’t make a difference how many dimensions there *actually* are, they just can’t see them. So they assume it really is two, because they never see more than that. You believe what you see, and you see what you believe.
Now here’s the thing, what happens if their universe isn’t actually 2D? Take that piece of paper they live on and push the two sides towards each other so it turns into an upside-down U-shape. From their perspective, nothing has changed, everything still looks like it’s 2D because they simply can’t see *that* direction. But their universe, as whole, is actually 3D.
Now what happens when the one flattie walks over to her brother? Well we know through the First Law that objects will not change its motion unless a force acts on it, or in other words, they want to travel in a shortest distance. To you, that shortest distance is clearly outside of the paper, but again, they can’t see that, to them, that shortest distance is along the surface of the paper, in the shape of a U.
So, that means **every step they take, the universe forces them to move in a non-obvious direction**. And how do they interpret that? Well if you’re not moving in a “straight line”, there must be a force acting on you – that’s what the First Law says, right? So what is this force that we cannot see but seems to be coming from the ground? Well, let’s call it “gravity”.
So what is the force of gravity in their universe? Nothing. It’s just geometry.
You can see where this is going. We do not live in a 3D universe, it’s actually 4D, and just as the flatties can’t see curved space in 3D we can’t see the curved space in 4D. You bent the paper with your hands, but here in our universe there is an effect where the local density of energy causes a sort of similar bending (but more complex). You could imagine this in flatland by drawing the flatties on paper using watercolors, the paper will crinkle up where you paint, so in their universe there is an effect where the local density of flatties results in more curvature. Of course, it’s much more complex, but you get the idea.
So when you try to walk from A to B here on Earth and the ground keeps hitting your feet, it feels a whole lot like something is pulling you down to the ground. But it’s not that, it’s more like the Earth and you are moving in different directions in 4D, and due to the local curvature those two paths intersect. And they always will, because of the form of that curvature.
Now this does leave one bit unexplained. You’ll note that you’re still getting pulled into your chair even if you’re *not* moving from A to B. Well that’s because there’s one odd thing about this 4th dimension, its always moving. Want to see it? Look at a clock. Notice it keeps changing? Well guess what, that’s your location along the 4th axis. So even though you seem to be “sitting still”, nope, sorry, you’re still moving. And since you’re moving one way, and the Earth another, boom, “gravity”.
So wait, *why* is this 4th dimension always moving? Because the universe exploded. The Big Bang, remember that thing? It’s not something that *happened*, it’s something that’s still going on, the Big Bang is name for when it *started*. You can call it “universal expansion” or lots of other things, but it’s all the same effect… we are getting bigger in 4D.
There is nothing pulling on you. There is no “force”. You’re going along a path that is the shortest distance between today and tomorrow, and the Earth is on a different one, and they intersect.
So, back to the question… What is gravity made out of? Nothing. Its just the shape of the universe.
Latest Answers