I thought Max Tegmark's commentary on why we haven't discovered extraterrestrial life yet was reasonable: http://www.youtube.com/watch?v=GctnYAYcMhI http://www.

I thought Max Tegmark's commentary on why we haven't discovered extraterrestrial life yet was reasonable: http://www.youtube.com/watch?v=GctnYAYcMhI http://www.youtube.com/watch?v=GctnYAYcMhI Basically he purposes that there is either a barrier somewhere before our point of biological progress or after; as he explains in the video, the desired reality is that we have already surpassed that barrier. He reasons that space travel is a simple engineering challenge compared to evolving intelligent life on the cosmological scale, so there's less reason to believe the barrier lies after our point of progress.