Physics defines space and time by standard rulers and atomic clocks. Objects that enter the same space at the same time collide and change their movement, so it was assumed that matter only moves when other matter hits it. Yet gravity ignores this convention, as the sun holds the earth in orbit from millions of miles away, with nothing between but space. How then does it do that?
Einstein’s answer was that matter can change space and time. Special relativity lets moving matter alter its time and space, and general relativity lets large objects change the time and space of objects around them. The equations work but don’t explain how matter changes time and space, and Einstein gave no rationale for his equations either.
Particles don’t help, as a particle can’t change the space and time it acts within, any more than a painting can make the frame enclosing it smaller, or a movie slow down the projector running it. Yet space contracts and time dilates, so how can matter change what it exists within?