Only massless 'stuff' can cross space at 300 million meters per second. But the 'meters' might be subject to compression. See science fiction, our only lodestone now. Galaxies may have zero to a billion civilizations; a range of estimates that stands near useless. Anyway, this galaxy has at least one. Civilizations might communicate via electromagnetic fields (at 'C'), but the vast distances and 'one over R squared' dispersal of energy make that seem a waste of time and effort. The possibility of meeting is tied to the possibility of distorting space. More advanced civilizations might be meeting even now. Or destroying each other out of fear (see Liu Cixin). If they notice us and what we say and do, well, we might not attract their attention.
