When I started college there was an orientation lecture by a special guest -- Carl Sagan. He asked us what we thought the probability is that there is life on o

When I started college there was an orientation lecture by a special guest -- Carl Sagan. He asked us what we thought the probability is that there is life on other planets. The guy sitting next to me mumbled "50-50". Dr. Sagan said "50-50". He said there was no data on either side, and without it, 50-50 was the only probability he could assign to a binary question.