system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How can space bend? or have curvature?

Where is coming from: I have a stress ball in my hand... I was squeezing it...then I started thinking about space while watching the stress ball now I'm confused as hell. I don't have sufficient knowledge to frame the question succinctly so I will explain.


If space can bend i.e.is "pliable", does this mean it exists "within" something else? What does it bend into?

If a two-dimensional "space" object can only "bend" by moving through a three- dimensional space (like bending a piece of paper?), does this mean that a three- dimensional space can only "bend" through the fourth or fifth dimension?

Please ELI5 so I can get back to work.
gpt
Whether or not our universe exists within something else is unknown at this time, and likely will not be known given our current understanding of physics, simply put, the boundary is accelerating away from us too fast for us to ever catch it.

What is often meant with "bending" of space time is how gravity distorts the path of objects.

Imagine, for example, rolling a marble across a perfectly flat friction-less surface.  If no one else touches the marble, we can expect that it will move in a straight line forever.

When space-time is bent, it changes the outside perspective of what that straight line is.  So if we have a massive object (a planet / star / black hole / galaxy / someone's mom), it bends space-time due to it's gravity.  An often used analogy is the bowling ball on a trampoline.  If you roll that same marble across a bent surface, you're still imparting the same energy on the marble, but from your perspective, it does not move in a straight line.  

Now, with a trampoline, we see that the surface has a slope, but empty space cannot have a slope as it's not actually made of anything.  Thus we say that space-time is bent, as forces unseen are acting on the marble and altering it's path.  It is often said that gravity is not a force (such as hitting an object with another object, or magnetism, etc.), but a consequence of mass existing in an uneven distribution across the universe.

[Physicists; I've deliberately simplified a few things to make it a bit easier to understand in ELI5 style, be kind.]