Could LIGO Find MASSIVE Alien Spaceships?

This is indeed a fascinating premise, and while it does seem quite outlandish to envision planet-sized alien spacecraft accelerating to near light speed, the exploration of such ideas pushes the boundaries of our scientific knowledge and stimulates our understanding of the universe. In all reality, our knowledge of the universe is still very limited. We've only just begun to probe the universe using gravitational waves. As we've seen, new and unexpected discoveries have already been made, such as the observation of black holes merging and colliding neutron stars. It's not unreasonable to expect that we'll continue to make surprising discoveries as our technology improves and our understanding deepens. Moreover, the search for extraterrestrial intelligence (SETI) has traditionally focused on detecting electromagnetic signals, like radio waves, from civilizations in space. The idea of using gravitational waves as a new way to search for advanced civilizations adds another layer of possibility to the ongoing search for life beyond Earth. Even if the likelihood is incredibly slim, it's an idea worth exploring. As you mentioned, the universe does weird stuff all the time. It's just a matter of us learning to recognize and understand these unusual occurrences. Even if we never detect an alien RAMAcraft, the insights we gain from considering the possibility will likely prove valuable in unexpected ways.