the nature of gravity in the sense of how it works in a 3D universe

Question

I need help with an analogy here because I simply don’t know/can’t visualise the true physics here.

Many people use an analogy for gravity acting on space-time as a sheet of material stretched across a plane and a heavy object in its center acting as a celestial body.
This is great for envisioning orbits, the curvature of spacetime and so on.

Now this is a “2D” sheet/plane that deforms “downward” in the 3rd dimension, I get it… But how does it translate to the actual universe? The universe is always 3D in all directions, isn’t it?

I’m stuck here guys, science help me!

In: 81

Answer 1

“Gravity tells spacetime how to bend, spacetime tells mass how to move.” That ‘heavy object on a bedsheet’ analogy is a 2-D representation of something we can’t really easily visualize in 3-D, which is the actual shape of space itself being warped by gravity. Mass moving through that space moves differently because of the geometric shape of space has warped.

Another way to envision gravity is to imagine spacetime as a fluid being sucked into a gravity well. If that gravity well is deep enough, it will flow quickly towards it, causing everything in it to be caught in the ‘current’. If it is very deep, it will flow faster than the speed of light – now you have a black hole, where spacetime is rushing into the center faster than the speed of light and nothing, not even light, can escape.