Well… some things may actually be impossible… and I even wrote an essay about that a little while ago: https://www.stephenwolfram.com/publications/recent/fqxi09/

Some things may happen gradually; others may be the result of a sudden discovery.

I’m guessing “AI” (with some footnotes about what it means) will happen gradually, as will the merger of humans with machines.

Something like cryonics might happen suddenly. Effective human immortality will probably be gradual.

I’m guessing faster-than-light travel is outright impossible in the way we currently think about it. But somehow when our existence is more virtual and distributed it may seem like less of an issue.

Extraterrestrial intelligence: I’ve been interested in that one for a long time… I have a bad feeling, though, that the question doesn’t even really make sense. As a consequence of the Principle of Computational Equivalence, lots of things in our universe should really be thought of as “intelligent”… and we have to be more specific, asking about human-like civilization histories… and that’s a very different story.