curious children

a note about the trampoline metaphor (because i have misunderstood this metaphor in the past): what is meant is placing heavy objects on the surface of a trampoline, without any bouncing, and then one observes the bending and stretching of that trampoline surface.

leaving eli5 territory, you imply that they are different, when really, special relativity is a special case of general relativity, the general case. special relativity is general relativity, but while ignoring gravity.

in more technical terms, in general relativity, the metric varies in space according to masses in space (contributing to gravity), while in special relativity, we simplify and have a constant metric (minkowski metric, minkowski space). getting away from the technical stuff: this means that in special relıtivity, changing frames of reference is easy, we can take very simple linear transformations of space. like when you hear "space and time is relative" and then one sees a change of reference, like "what if we look at it from the perspective of this person moving fast, as if they were stationary", it is a simple transformation of spacetime, basically transforming it uniformly. this is in contrast to general relativity, where we stretch and squash and warp spacetime nonuniformly.

also a nitpicky note about special relativity and "aging": it is not as simple as "moving fast means aging more slowly" (as of course, who is traveling fast and who is stationary is indeed relative). acceleration (the change of velocity/speed and direction performed for the return trip) is needed to explain this.

instead of the aging thing, which in my opinion is complicated and difficult to explain, especially intuitively, it is more intuitive to explain the classic examples of shining a flashlight on a moving train, or having two lightnings strike the front and back of a moving train at the same time from the perspective of an outside observer.