How does the fabric of space actually works?


If it works exactly like a ball that is placed on top of a cloth, doesn’t the celestial bodies that is rotating around the ball will eventually get sucked into the center?

In: 2

Some will, some won’t.

If a body is just far enough away from the “dip in the cloth”, and is moving away from it at just the right speed, at just the right angle, it won’t. This is called “orbit”.

Otherwise, yes. This is called “gravity”.

The ball and fabric demonstration are good metaphors to help with visualisation. But it has a component that space doesn’t: friction. So when someone uses it for a demonstration the “orbiting” object always falls to the center because it is constantly being slowed by friction while its rolling. Moving through space alone doesn’t have friction.

Yes, but the “friction” of spacetime is in form of _gravitational waves_. It takes an extremely long time for it to slow down enough. Even with black holes, the most extreme example, it takes billions of years; for a planet around a sun, the universe is simply not old enough (yet).

That analogy is OK for getting a very general idea of how gravity can be viewed geometrically, but it’s a very oversimplified picture. The biggest flaw is that it makes it seem as if the “warping” is all in space, but that’s simply not the case. See, in general relativity, (Einstein’s model of gravity, which is the best model of gravity we currently have), space and time aren’t independent entities, but rather different components of one thing, which we uncreatively call “spacetime”. So, in the simple fabric analogy, the fabric represents not *space* but *spacetime*. And, here’s the key point, except in very extreme cases like with black hopes, almost all the “warping” of spacetime from massive objects happens not to the space components of spacetime, but to the time component. So, objects even as massive as planets have very little affect on the *space* surrounding them — instead, the gravitational affect they have on nearby objects is mostly an effect on those objects’ *time* trajectories.

This video does a really good job of breaking this all down and giving an intuitive and *visual* understanding. It’s one of the best ELI5-type explanations I’ve seen on any topic precisely because of how visual it makes things. In actually specifically starts with the simple ball on fabric picture, explains the problems with it, and then, piece-by-piece, fixes the problems and ultimately ends up with something much more accurate and yet still as intuitive as possible. I came across it a couple years ago and it really stuck with me.

No. I’m sorry for so many conflicting answers on here. In your analogy, you’re referring to “the shape of spacetime”.

So the “shape” of spacetime is like a cloth wrapped around a ball. It is also just the surface of a ball. But the surface of the ball contains our entire 3d universe There isn’t any middle for anything to fall into. There is nothing above or below the surface of the ball. Moreover, that nothing above and below the surface of the ball isn’t “nothing” like space is a vacuum, it’s just not.

To explain a different way, the shape of spacetime is “the surface of a sphere” and it isn’t “a sphere”.

It’s really strange to think of the universe this way because it doesn’t make sense to or 3d minds. If you think it is strange or weird or didn’t make any sense, then you’re on the right track.