Space is shorthand for “There is nothing there” So, how does one compress that?
Put the government in charge of it.
There will be a shortage of space in a jiffy.................
The thing is, if you read Einstein carefully, he never says that gravity is produced by warping space. Never; not a single time. It's a common misunderstanding of his theory, but it's not a part of relativity at all.
What Einstein said is that gravity is an effect of warped spacetime, and he also agreed with you that space itself is not a physical thing that could be warped or compressed.
So if spacetime is just a combination of time and space, and the space itself cannot be warped, then that only leaves the time element. That is the thing that is actually being warped to produce the effect we see as gravity. Gravity is an effect of warped time, not warped space.
Now, since time is just something we use to measure rates of change it might seem just as nonsensical to talk about warping time as it does to talk about warping space. But essentially what it comes down to is that things change at different rates depending on the density of matter and energy in their vicinity. Now why that is happening is the real question!
First of all, it’s spacetime; not space. And in either case, second: it is *not* shorthand for “nothing”!
If it were nothing, there’d be total chaos. There’d be no infrastructure there to determine which trajectories are inertial, which paths are trajectories in time, versus curves in space, which directions are temporal versus which ones are spatial, to determine what is congruent to what, which angles are right angles, which points are near which other points, which regions are contiguous to which regions, how many dimensions there are, which paths & motions are smooth versus jagged, the lengths of paths, the durations of trajectories, which speeds are light speed, etc.
That all counts as something. And all that infrastructure is what spacetime is and contains. In fact, everything else can be reduced to it (via Einstein’s field equation). Even the law of inertia is, itself, a consequence of Einstein’s field equation.
So, it’s not only not nothing, it’s everything.
You’re way behind the curve- Einstein already created the theory of relativity.
And many experiments proved it to be true. A black hole is proof of it.