1) it's a really big place. It's likely we can't see that far yet.
2) Will we be here a million years from now? Two million? Other civilizations could have come and gone dozens of times in our galaxy alone before we were here. And dozens may come and go after we're gone.
Why can't they see us? All the arguments for life say "the universe is so big there has to be more life, and highly advanced civilizations somewhere." Assuming that, sure, we can't see them. But why hasn't some advanced civilization seen us?
- some have, and have responded, but we aren't looking for them in the right place and in the right way
- humans have only been able to actively send information into space since only about the 1950s (radio waves), and physics dictates that locations 80 light years away are just now starting to see that, provided they are looking in the right location and in the right way (and that they are technologically advanced enough to do so.
- It could be that a sufficiently advanced civilization no longer has the capability to receive and transmit long-wave radio communications. Just like many computers now don't have any way to read a floppy disk, or if someone were trying to communicate via smoke signals, you'd be hard pressed to find anyone who could understand it.
- Space is so large that if a civilization several hundred light years away (an insignificant fraction of the size of our one galaxy, actually) sent us a message that we received and responded to, it's possible they could have collapsed by the time they receive our response. The converse is also true, they could have 'seen' us and sent a message, and we could collapse before we had a chance to receive it and respond.
We may feel special, but that's only because we haven't found anything else. If they found hundreds (or more) of worlds like ours, then maybe we're just another dot on their galaxy map.
Plus if the media is anything to go by, all we do is shoot each other. Might not be too exciting for a civilization who can travel amongst the stars.
Just seems unlikely that we assume, because the universe is so big, there are advanced civilizations out there - but not ones that can find us, not ones that we can find, for various reasons discussed in these threads.
If our understanding of the universe is true to a certain point, civilizations are far more likely to be essentially alone and "special" than many might think.
Is there a similar abundance of planets with life in the universe?
The deal is, if we were one among hundreds or thousands, what are the odds nobody at all in any of those other civilizations would want to interact with us? Because we've received zero interactions. Dead silence.
Why is that? Well, it takes a lot of energy to broadcast, so they'd have to beam us a message. We're not really looking for beams. Don't even know what they'd look like? Laser pulses? Soliton trains? Neutrino bursts?
And if that is accurate, then essentially we ARE alone in the universe. There simply isn't anything close enough - we'll be enveloped by the sun or some other catastrophe before that happens.