Edit: I mean a new concept as in new with regards to the century before. I'm aware that lorentz and maybe others had some idea even before GR So time slows down for the individual under a stronger gravitational field than for an individual under a weaker gravitational field. But why does this nessicarily have to go against common sense? Can't it just be thought of as the gravitational field slowing down all the physical processes of an object? Say Alice is under heavy gravity compared to Bob. Well, Alice's physiological processes would be slower. This doesn't contradict common sense, as sometimes, things move slower in general( something moving through viscous fluid for example). It's just that somehow under higher gravity, everything for Alice, her molecules, the molecules of the immediate environment etc, would move slower in unison compared to everything in Bobs enviornment. Well, if her physiological processes are slower due to the field, then of course Bob would perceive her to be aging more slowly. So then why do so many people consider this time dialation to be almost "mystic". Why would we need a correspondence principle? It doesn't really go against our a priori intuitive understanding of reality if thought in that way.