Earlier quoted context omitted.
Space itself means the metric of spacetime: how you measure distances. Locally, if there was no gravity, you could think of space as a plain reticule where distances would be calculated through eucledian geometry: that means cartesian distances, parallel lines would be parallel and the angles of a triangle would sum 180, and the shortest path between two points is the straight line. General Relativity successfully es…
If this is ELI5, we hang around very different kinds of five year olds :-) Joking aside, thank you for the deeper explanation. The idea that spacetime isn’t fundamental is a very non-intuitive concept given how we’ve evolved to interact with the world. Any suggested reading on this topic for laypeople?
let's think about space like a giant, invisible playground. Normally, it's flat like your bedroom floor, where you can measure how far your toys are from each other with a ruler straight across. That's like when there's no gravity in space.
But guess what happens when something really heavy, like a big bowling ball (that's like a star or planet) comes into your playground? It makes everything around it bend and curve. So, the distance between your toys is no longer a straight line. It's like when you throw a ball, it doesn't go straight, it goes in a curve.
This bending is what a really smart guy named Einstein explained in a thing called General Relativity. He came up with a way to measure how space bends around heavy stuff.
And you know what else? There's this really weird stuff called Dark Energy that's everywhere but we can't see it. It makes space grow bigger and bigger, not because of heavy stuff, but because there's a lot of empty room. Scientists are still trying to understand this, but it's like blowing up a balloon: even though there's no heavy stuff inside, the balloon still gets bigger!