I really like thinking about this problem. From a layman's point of view, it often seems to me that people fail to fully account for the impact of time once intelligent life has arisen. Consider the technological advances of the last (just over) 100 years. We went from being a ground-based species to mastering flight, confirming the concepts of Relativity, unlocking the energy the atom, landing on the moon, sending robots to other planets and most of us now carry a device in our pockets that connects us to every other person on the planet and provides access to almost all of human knowledge. Consider what could happen in another 100 or 500 years, which is nothing on the cosmological scale. At this rate, it seems likely that we will achieve a technological singularity within 50 years that will move us closer to things like virtually free, clean energy, genetic modification, machine fusion and who knows what else. I'm sure there are things that we will come to understand in the coming decades that we can't even articulate as a subject matter today.
So, my point is that if we can imagine it, we will eventually do it. Notwithstanding an extinction event (external or internal source), we will begin colonizing planets and we will begin traveling to other solar systems eventually. Regardless of the difficulty of the physics, we will find a way.
From what we understand, statistically, ETs must be there. And yet, we see no signs of them. My theory is that life and consciousness become something we can't even understand at the moment, which is why we're not seeing what we're looking for; we don't know what we're looking for, we don't know where to look (they may be in other dimensions) and we don't know how to talk to them. Once thing is for sure, the next few generations are going to see some crazy shit, whether it be immortality or the whole planet getting aloha snackbar'd is difficult to say.
