Is there alien life forms out there? Carl Sagan posited that the numbers imply it's inevitable. In one of my two college astronomy courses, we went through the best numbers available at the time and they indicated that not only is life of SOME sort out there, but there is intelligent life out there somewhere. The professor also noted that there is virtually NO CHANCE that we would ever come in contact with them as the sun will expand and swallow all the planets out to Mars before mutual contact is likely to be established.
So with that knowledge I read today that the current estimate is that there are 17 billion earth sized planets in OUR galaxy. 17 billion! I don't remember how many we thought there were 25 years ago in class as there were a lot of 10 to the nth powers being thrown around. I think we were talking about 10% of suns having an earth sized planet and this revised figure indicates the number is closer to 17%. Regardless, that's a pretty big number of planets the size of earth in just our galaxy. There are estimated to be 125 billion galaxies in the universe (don't get me started on theories of how many universes there are). So math says there are 2.125 trillion planets the size of earth (given the assumption that other galaxies are similar to ours in size and relative density of earth sized planets.
So is there life out there? Yes. Is it like ours? Maybe. Will we establish contact with them? Well, it seems a bit more likely knowing there are likely 17 billion earth sized planets relatively nearby.