The brief summary is that we observe two things: (1) we exist, with the full set of memories we have, (2) these memories don't include any evidence of other intelligences (I'll assume - readers who think they've ridden on UFOs can draw other conclusions).
The existence of our particular civilization (in all its detail) is more probable if intelligent life is more probable in general (assuming one dismisses arguments about infinite universes containing all possibilities, so you can never conclude anything from anything).
But if intelligent life is generally more probable, it's more probable that we have seen other intelligent life, contrary to observation.
So the most likely situation given what we observe is a compromise - intelligent life is fairly likely (explaining our existence), but not really likely, or at least not really likely to explore other stars (explaining why we haven't seen any aliens).
One unfortunate possibility is that intelligent life reaching our technological level is common, but getting to the level of colonizing the galaxy is uncommon. But that needn't be highly likely. It's also possible that there's other intelligent life out there not far away, in which case it may well be within our ability to detect it with a bit more effort. That's what one would conclude from this article as well.
The brief summary is that we observe two things: (1) we exist, with the full set of memories we have, (2) these memories don't include any evidence of other intelligences (I'll assume - readers who think they've ridden on UFOs can draw other conclusions).
The existence of our particular civilization (in all its detail) is more probable if intelligent life is more probable in general (assuming one dismisses arguments about infinite universes containing all possibilities, so you can never conclude anything from anything).
But if intelligent life is generally more probable, it's more probable that we have seen other intelligent life, contrary to observation.
So the most likely situation given what we observe is a compromise - intelligent life is fairly likely (explaining our existence), but not really likely, or at least not really likely to explore other stars (explaining why we haven't seen any aliens).
One unfortunate possibility is that intelligent life reaching our technological level is common, but getting to the level of colonizing the galaxy is uncommon. But that needn't be highly likely. It's also possible that there's other intelligent life out there not far away, in which case it may well be within our ability to detect it with a bit more effort. That's what one would conclude from this article as well.