I recently read a book by Ben Bova, an engineer and sci-fi writer. One of the topics he discussed is that of interstellar travel. He posited that if aliens used something like antimatter as propulsion for interstellar travel, we should be able to see them because of the large amount of energy that would be created. His explanation is that quasars could be alien spacecraft that are currently moving away from us near the speed of light resulting in the large redshift. He had a reasoning for craft moving toward us also but I don't recall that one. Anyway, he also mentioned that his idea could be disproved but only with some advanced knowledge of cosmology. Since I have no advanced knowledge of cosmology, I was wondering what you guys think of Bova's idea.