Is there a non physics explanation to help people understand how space (which I thought is nothing) could be curved?
Will you accept a mathematics explanation?
"Curvature", as the term is used in relativity, is a mathematical term. It is defined in terms of the distance metric (as generalized to include time).
To illustrate, consider a cylinder (the surface, not the solid). On the cylinder, we would measure distances as the shortest path along the cylinder. Mathematically, the cylinder is flat, so not at all curved. This corresponds to the fact that you cut cut down along the cylinder, and open it up so that it is flat, and you could do this without changing any distances (not counting those where the shortest path crosses the cut-line).
Take out your atlas, and look at a Mercator projection map of the world. It is really an unwrapped cylinder. Think of it as a cylinder, with the left and right side taped together where they match. Now, let's suppose that we scrap our current way of measuring distance on earth. And, as a new distance metric, we use the old distance between the two places on the Mercator map. We could scale it, say one inch on the map = 100 miles on Earth. This will be a different distance metric than we ordinarily use. With this new metric, the north pole and the south pole will be an infinite distance away. With this new distance, the earth is flat.
When physicists talk about curvature of space (or space-time), the metric they are using is based on light travel. The distance between two points is determined by the time it takes for light to travel between them. This was adopted as the standard for distance, following the Einstein conclusion that the velocity of light is the same for all observers.
I hope that helps.
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