Space and time in physics aren’t just mental concepts but reality properties measured by rulers and atomic clocks. When objects try to occupy the same space at the same time they collide and the particle model assures us that this is the only way that matter interacts. The problem is that gravity ignores this restriction. It lets the sun hold the earth in orbit around it even though they are millions of miles apart and with nothing between them but space.
Einstein’s solution was that matter changes the reality context, by altering time and space. Special relativity asserts that a moving matter object alters its own time and space and general relativity asserts that large objects change time and space for other objects around them. The equations work but they don’t say how matter manages to change time and space. How can mere matter change the time and space it exists within?
This problem is why quantum theory can’t replace relativity. The standard model works via particles but what particle can alter space and time? That would be like a painting making the frame it presents within larger or smaller! The nub of the quantum-relativity theory clash is that no graviton particle has ever been found and probably never will be. This leaves physics with two grand theories, one about particles and the other about their space-time context, with no common ground at all.