Intelligent life can and does exist within our Universe. The anthropic principle -- that we ourselves are here -- prove that life is possible and also that life itself is possible. The conditions for it have happened at least once and with the vast size and age of the Universe it is bordering on statistically impossible that it doesn't exist or hasn't existed somewhere else at some point.
Now, if intelligent life is common, Fermi's paradox would seem to come into play because we have not been contacted yet. Realistically, however, we've made our presence known for such a short period of time (by broadcasting waves into space) that it's unlikely to expect a response yet.
If intelligent life is uncommon, though, it's next to impossible to ever encounter it again due to the incomprehensibly vast size of the universe.
At the same time, it's possible that ancestors of humanity have been contacted by alien races. Any sufficiently advanced technology would seem indistinguishable from magic or divinity. That's kind of useless conjecture, however.
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