eli5 how do massive objects deform space fabric like a ball on a sheet?


I understand the thought experiment in itself but I dont understand how it interacts like a heavy object on a sheet. If I were to take a ball and place it inside of something 3 dimensional it would press out, not in

In: 0

It’s a *metaphor* to help you understand how gravity comes to exist.

**Like** how a ball on a sheet warps the 2-dimensional plane, causing smaller balls to roll toward it, so too a mass in 3d space “bends spacetime” so that other 3d objects are attracted to it. This is gravity.

**How** this happens is very hard to understand. Or maybe I’m stupid – either way, I don’t know how it happens.

They don’t. Mass curves space towards it. The more mass there is, the more it curves, and the closer you are to it, the more it curves. A ball on a sheet has those properties: a bigger ball bends the sheet more, and the sheet is bent more closer to the ball. That’s about where the similarities end. It’s a useful introductory metaphor, but it doesn’t work as a model of physics, even if you scale it up to three dimensions.

As for how massive objects bend space at all, the best answer we have right now is “they just do.” As far as we know, that’s just how the universe works. If there’s mass (or energy), space gets bent.

Watch [this video](https://www.youtube.com/watch?v=wrwgIjBUYVc) actually, because it shows a better representation of what’s going on. The old ball-on-a-trampoline example uses gravity (Earth’s gravity) to explain the supposed gravity of the heavy bowling balls, and it’s just confusing.

What you’re seeing is not that gravity “sucks in” space, but rather a space and time deformation (because we’re constantly moving in time).

They just do. The ball on a sheet is an analogy meant to show how curved space can make straight lines suddenly not be straight. It’s not actually accurate mathematics.