I had a doubt regarding space-time grids... I just don't understand, if the universe is three-dimensional (excluding the time dimension) why do we represent the universe as a single 2D fabric of grids as seen in various internet photos?
For example, Mercury's orbit tilts 3 dimensionally with respect to the sun, my question is why is it represented as just a single 2D sheet spread across space with respect to the view of the solar system where the universe is 3-dimensional.
Earth doesn't have the same orbit positions as compared to other planets, one can be between the $y$ and $z$-axis and the other on the $x$ and $z$-axis, etc. Why is space-time grid just spread across space on a single sheet cause if the coordinates are different we can't form a sheet?
Why?
