I sometimes wonder about the odds of the most chilling questions. What are the chances we're the only intelligent life currently in existence? ("We" including other primates, dolphins, etc.) The only intelligent life to have ever existed? The only intelligent life to have ever existed and that will ever exist? Even the first and last instance of any kind of life at all?

For a long time, I thought surely these probabilities must basically be zero, due to the sheer amount of dice that can be rolled (tons of space + tons of time), but after hearing a lot of smart people talk about it, I think all of these things do carry a non-zero possibility.

Of course, we'll probably never know, though. There could be some galaxy clusters teeming with life and visible structures but they could be so incredibly far away from us that they basically don't exist from our perspective, and vice versa.

I'm not so sure. I recall seeing calculations that show that, unless an intelligent species was deliberately sending out very high energy, very well targeted signals, it's really unlikely we'd detect them.