Robin Hanson gives a talk (starting at 5:31) and addresses questions afterwards on building a plausible story (although perhaps unlikely) of UFA/UFO aliens.
Yes, the universe looks completely dead; we see no signs of life outside Earth, even though over millions of years advanced aliens could have made some big visible changes. Some possible explanations:
1. Aliens arise so rarely that the nearest ones are too far to see, or to have traveled to here,
2. Aliens are common but simply can’t travel between stars or make big visible changes,
3. Aliens are common and travel everywhere, but enforce rules against visible changes, or
4. Aliens arise rarely, but in small clumps; the first in clump to appear can control the others.
Of these, only the last two can put aliens here now, and #3 seems too much a conspiracy (i.e., coordinate to hide) theory for my tastes. But scenario #4 works, and could plausibly result from “panspermia.”
That is, simple life might have arisen on a planet Eden long ago, via a very rare event. (My research suggests this happens only once per million galaxies.) After life evolved at Eden for billions of years, a rock hit Eden, kicking up another rock that drifted for millions of years carrying life to seed our Sun’s stellar nursery. A nursery that held thousands of new stars packed close with many rocks flying around, allowing life to spread quickly to them all.” Many thanks to those who participated in the Q&A session.