As told in certain science fiction, I like to imagine that dark matter/energy is the "pollution" or other side effects caused by some alien civilizations [over]

As told in certain science fiction, I like to imagine that dark matter/energy is the "pollution" or other side effects caused by some alien civilizations [over]use of faster-than-light travel. Which is actually a terrifying existential threat to think about: The more an earlier civilization uses FTL, the more space will expand, and eventually it will become all but impossible for younger civilizations to traverse space without becoming dependent on the elder races.