If something is physically possible to do, then some alien civilization -- many -- will have already done it: look to the heavens for evidence of it being done. If you don't see evidence of it, then it can't be done, perhaps due to difficulties we have not discovered yet.
Vaguely reminiscent of Rule 34 of the internet.
Problems with this reasoning: If it is physically possible for intelligent life to exist in this universe, then there should be plenty of astronomical evidence of its existence. Some things may be possible, but might take billions of years or longer for an alien civilization to accomplish, but the universe isn't yet old enough for us to see evidence of their accomplishments.
Previously, tapping quasars.