system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: A common model for gravity’s effect on space is a sheet of elastic material with some stuff put on it to make wells and such. But how does that apply in 3D?
gpt
The whole "rubber sheet" model is effective for the limited number of dimensions that we can visually represent. If you wanted an accurate representation of the effect of some mass (e.g. a planet) on spacetime, you would need to make in at least four dimensions (three for space, one for time). The problem is that we cannot draw a truly four-dimensional (or *n*-dimensional) picture - we exist in and directly perceive three spatial dimensions, while time is perceived as sequential differences.

The solution? We exclude something. In the case of a drawing like "the Schwarzchild radius of a black hole," this looks like a "bottomless" funnel around an infinite mass. In the rubber-sheet depiction, it appears as a depression in an otherwise flat surface. Trying to add dimensions simply does not work - even if the underlying physics is true for the additional dimensions - and so to represent a system completely we need multiple such reduced depictions.