Let me say, I HOPE and would be so excited to think we are actually going to meet an alien civilization in our lifetime. To me it would be the biggest event in human history with incredibly profound consequences.
But my long obsession with astronomy, astrophysics and all things nerd when it comes to our cosmos has me doubtful that this will happen anytime soon.
There's huge obstacles for not only us, but those aliens out there for us to find each other. Here's my list of why I think we're in for a long wait to make first contact.
#1. The size of our known Universe. Its staggeringly huge, so big in fact its incredibly hard for us to even imagine the hugeness. By this sheer fact, even if life is very common in the Universe and advanced alien civilizations are out there exploring right now, its still very unlikely for us to make contact.
#2. Tied to the first one, because of the size of our cosmos, another huge hurdle is traveling vast distances. The laws of physics as we currently know them prevent anything faster than the speed of light, and even if we could travel 99.999999% of the speed of light, a short journey to our closest neighbor Andromeda would take 2.4 million years to say hi. The time for the traveler would be short, but is it worth traveling when you come back to earth 4.8 million years have passed. *see note at bottom.
#3. If Aliens are aware of us, its highly unlikely they would not attempt contact, even though we all love Star Trek's prime directive and how noble it sounds. Because intelligent life recognizes others like it, you'd have to assume they wouldn't come all this way just to not say hi.
#4 Slightly more abstract, but if you red Carl Sagan's Demon Haunted world, you'll see that humans have this long standing tradition of seeing demons, witches, ghosts, angels, and now more recently Aliens. The book goes into much more detail so you should just read it and be cool like me.
Lets listen to Carl explain why we're still waiting for first contact.
Often people bring up the radio noise from earth being heard by alien civilizations and that would bring them to visit us, mostly this is because they saw the movie Contact with Jody Foster
To see why this is unlikely, go to 2:38 of this video to see how much space our radio signals in our Galaxy, spoiler, its tiny.
Finally because he's so awesome, lets her today's modern Carl Sagan, Mr Neil deGrasse Tyson on UFO's:
* I'm going to touch upon this since it will be brought up. I am aware it is very possible advanced civilizations have technology to bypass the time/distance issues I'm talking about; however it might simply not be possible, we have theorized about wormholes, folding space/time, etc.. However its also very possible we cannot go around the laws of physics, and we are stuck only being able to exist and explore in first person our own solar system and not much more. Leaving real exploration to robotics, and AI intelligent creations of humans in the future.