Einstein's general relativity says gravity is spacetime curvature, but what does that mean? Let's take a look at how gravitational time dilation results in a...
It’s just meant as a physical analogue to demonstrate some features (namely how the shape of the sheet/gravity affects things that travel on/through it) in a way that people can understand easily.
This is a pretty accessible visualization of gravity.
https://youtu.be/b9XhexlQMZw
But it’s kind of a terrible one, because it uses gravity to explain gravity.
If it’s the demonstration I’m thinking of, it uses gravity to visualise the affects of an otherwise invisible force.
It’s just meant as a physical analogue to demonstrate some features (namely how the shape of the sheet/gravity affects things that travel on/through it) in a way that people can understand easily.