Robert J. Bradbury, <email@example.com>, writes:
> The only statements that can be made with putting yourself squarely
> in the swamp is: "We don't see aliens that are our size nearby
> (literally walking around on earth)" and "Aliens do not appear
> to have restructured or consumed *all* of the stars in the galaxy".
I think you can make some stronger statements than this. With regard to the first statement, you can also say that there are no aliens or alien artifacts big enough to be visible on the other solar system bodies we have observed. You can say that there are no aliens on earth larger than elephants (land aliens, anyway). You can say that there are not too many aliens the size of insects, at least not in areas where people live. You can probably also put some limits on the amount of energy any hiding aliens on earth are using.
With regard to the second part, you can say that if aliens do restructure/consume stars, they appear to prefer small stars and avoid large ones (and then we must interpret microlensing events in a certain way). You can say that if they do this, they apparently do it to virtually all the galaxies we can see clearly (since all have similar missing mass), and all aliens follow the same policies in this regard. You can probably derive something from the fact that dark matter appears to be spherically distributed, while most visible/unmodified stars lie in the galactic plane, but I'm not sure what that tells us about the aliens.
Overall you can say that intentionally or accidentally, the aliens are creating a universe which looks a lot like one which could have evolved naturally.