Though both dark matter and dinosaurs are independently fascinating, you might reasonably assume that this unseen physical substance and this popular biological icon are entirely unrelated. And this might well be the case. But the Universe is by definition a single entity and in principle its components interact.
If our Galaxy truly contains many intelligent civilizations, some of which may be ahead of us by a billion years, how is it possible that we have not seen any sign of them yet? Nobody knows the answer to this so-called "Fermi Paradox," but one of the speculations is that there exists some bottleneck to the emergence of intelligent civilizations, and that this bottleneck could have either been in our past, or we will hit upon it in the future.
Scientists have assigned the role of Mister Answer to science, the source of knowledge on every subject. This is peculiar because science does not accept a complete body of knowledge at any one time as final, therefore no answer can be final. This is how science progresses. Scientists, though, often forget that.
Much of modern physics has been about exploring inherently invisible things, which seem to be far more common than the obvious things we experience with our senses. Yet these invisible things follow rigorous laws that allow us to test their existence in many ways. Here is a very short list of some of the "invisible" things that we routinely work with.