By Stephanie Pappas
How many intelligent alien civilizations are out there among the hundreds of billions of stars in the spiral arms of the Milky Way? According to a new calculation, the answer is 36.
That number assumes that life on Earth is more or less representative of the way that life evolves anywhere in the universe — on a rocky planet an appropriate distance away from a suitable star, after about 5 billion years. If that assumption is true, humanity may not exactly be alone in the galaxy, but any neighbors are probably too far away to ever meet.
On the other hand, that assumption that life everywhere will evolve on the same timeline as life on Earth is a huge one, said Seth Shostak, a senior astronomer at the SETI Institute in Mountain View, California, who was not involved in the new study. That means that the seeming precision of the calculations is misleading.
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