[shuzchen]

Numbers and math are required for theoretical space travel, but not necessarily for practical space travel. Catching a ball requires solving differential equations, but children and animals are capable of performing this action with no problem.

Given that there is so much of physics that we have yet to understand (assuming what we think to be true is actually true), and given the infinite possibilities of what forms alien life could take, you can't make any assumptions about what sort of language they'd have. This was a point they briefly tried to make in the movie.

[Latty]

Another way to do 'practical space travel' without 'theoretical space travel' is with tools. Just because you can't develop it with your language doesn't mean you can't use a tool someone else developed, or even an animal that evolved with the capability.