Near death experiencer comments on alien life forms....

There's no good evidence for "just 4", but there's very good evidence that there are at least 4. There is, however, no good evidence that there are more than four, either.

Like observing that objects can have length, width and depth (there's 3 orthogonal dimensions, right there), and that objects change over time (that's one more dimension).

That sounds to me like a fancy way of saying that our scientific generalisations (theories etc.) are based on empirical observations. All scientific theories of any value are "abstract generalisations", or rather models that allow us to predict how objects behave and how their possible behaviours are constrained.

Yes there is. For instance, we find that we cannot uniquely specify the location of a given point in the space we observe (say the location of an object, if you need a concrete example) using fewer than three numbers and some unique fixed reference point, using any possible method. That's empirical evidence for 3 spatial dimensions, right there.

Have you ever noticed how stuff doesn't all happen at once? Go figure.