answer:The size of the universe combined with the age of the universe makes the probability ridiculous. Consider that humans have only had written communication (And by that I mean the ability to convey specific thoughts with writing – not cave drawings that tell a vague story) since the 7th millennium BCE – so less than 10,000 years. And we’ve only been using radio waves for less than a hundred years. Presuming that the very first radio signal ever used by “Terrans” (1 August 1920) was picked up by an extraterrestrial, and if it were immediately answered, in order for us to have gotten the return message today, the planet could be no further than 46.5 light years away. There are approximately 2000 stars within 50 light years of Earth. An infinitesimal portion of the stars in the universe. And considering that one of those planets would not only have to have evolved intelligent life, but that such life would have to be capable of communicating via radio wave at exactly the time that our message reached them, and not 2 billion years ago or ten thousand years ago… it is just so unlikely. But, on the other hand, the fact that there is evidence of microbial life on Mars as well as on meteoroids that have fallen to Earth gives enough credence to the hypothesis of extraterrestrial life that it makes sense to believe that there may be advanced intelligent life out there somewhere, somewhen.