Ask Lemmy

Then you drew a line segment between points (1,1) and (3,1). You can stretch the rubber until it’s significantly longer, but your line is always exactly 2 units long, even if the rubber stretches.

Ah, but then we couldn't see or experience gravity at all!

In differential geometry there's a very important distinction between coordinate distance and actual distance. The globe and GPS coordinates give a good example - one degree of longitude is throwing distance at South Pole Station, but ~111km at the equator, even though it's still one degree. On a curved surface additive coordinates will never describe actual distance exactly. In some cases, like a 2-spherical planet, they're even guaranteed to break down somewhere (like the exact poles).

It was a blunder mentioning rubber - this isn't about bowling balls on a trampoline. I just meant that solid matter has a natural spacing between atoms, and if something continuously pulls it away from that - like expanding space or, I don't know, two conveyor belts going opposite ways - it's going to respond with a constant tension offsetting the effect. Or break.

The reason the planet orbits the star is that the star has warped space such that (given speed the planet is traveling) an orbit is a straight line.

And annoyingly, that's only possible in more dimensions than we can picture. All a 1+1 dimensional space can do is expand or contract.

Gravity is mass warping spacetime.