[baxtr]

>But there must be something else, all the new cruft contained in Relativity, like dilation of time and space.

Why must there be something else?

[kazinator]

To explain why everyone's interferometer measures the same light speed regardless of its orientation, or their relative motion past the same point.

[baxtr]

Ah ok got it.

Thought you were talking about something else entirely. Didn’t realize you meant the specialties of space-time in "special relativity".