Current scientific estimates are that there are about 200 billion stars in the Milky Way, so that means there could be at least 400 billion drifting planets in space, add to that the planets that orbit stars and the smaller free-floaters we can't detect yet. Well that means somewhere out there are between 600 and 800 billion planets give or take. The number is subject to upward revisions.
So what exactly are the possibilities that we are the only rock in the Milky Way that has somehow managed to sustain life. Not to mention we are only talking about the Milky Way, our galaxy. So, we are just talking about the local neighborhood and not the entire universe or universes depending on your nomenclature. And we are talking life as we define it, you know carbon-based in need of oxygen and probably H2O. Other life forms based on different chemical processes, well...
The point being - the intelligent, thoughtful question is no longer "Are We Alone Out Here?" but rather, "When are they going to find us or us them?" Of course, science fiction has speculated for a long time that we have already been found and they are simply patiently waiting for us to grow up or blow ourselves up, in which case they may just start over with another seeding of the Earth and hope the next evolutionary cycle ends with the survival of a rational, intelligent species that will contribute to the cosmic empirical experience.