This is an excellent example of 'thinking inside the boundaries of our paradigm'. Other civilizations may have discovered paradigms that allow them to traverse the galaxy in days, and even in seconds.
> If you think objectively about it, "physics paradigms far beyond our understanding today" do not necessarily exist.
That's what was said in the mid to late 19th century. Then quantum physics was discovered. It was already 'outside' our understanding then, and it still is. We take some things 'just as they are' and accept them, like quantum entanglement. We think we explain them through some unproven theories to avoid admitting the fact that they upended our earlier paradigm of how things are.
A lot of the things that are observed in the ufo phenomenon can be similar things if they are actual extraterrestrial civilizations 'observing' us. 'Shape changing' ufos, ufos that travel in a speed that no creature can withstand etc.