Humanity May Be Alone In The Universe -

Humanity May Be Alone In The Universe

There may never have been another intelligent, technologically advanced alien species in the entire history of the Universe. Last week, in the New York Times, scientist Adam Frank emphatically wrote that Yes, There Have Been Aliens, concluding that given all the potentially habitable worlds we know must be out there from our astrophysical discoveries, intelligent life must have arisen.
What he fails to account for, however, is the magnitude of the unknowns that abiogenesis, evolution, long-term habitability and other factors bring into the equation. Although it's true that there are an astronomical number of possibilities for intelligent, technologically advanced lifeforms, the huge uncertainties make it a very real possibility that humans are the only spacefaring aliens our Universe has ever known.

Back in 1961, scientist Frank Drake came up with the first equation to predict how many spacefaring civilizations there were in the Universe today. He relied on a series of unknown quantities that he could make estimates for, and ultimately arrive at how many technologically advanced alien species there were, at present, in both our galaxy and our observable Universe right now. With the advances of the last 55 years, many of those quantities we once could only estimate via guesswork can now be known to an incredible degree of precision.For starters, our understanding of the size and scale of the Universe has increased dramatically. We now know, thanks to observations made with space-based and ground-based observatories covering the full spectrum of the electromagnetic wavelengths, how big the Universe is and how many galaxies there are within it. We have a much better understanding of star formation and how stars work, and so when we look out into the grand abyss of deep space, we can calculate how many stars there are out there in the Universe, both now and over the entire cosmic history since the Big Bang.

That number is huge -- somewhere close to 10^24 -- and it represents the number of chances the Universe has had, over the past 13.8 billion years, to produce life like ours.We used to wonder how many of those stars had planets around them, how many of those planets were rocky and capable of having atmospheres like our own, and how many of them were the right distances from their stars to have liquid water on their surfaces. For innumerable generations, this was something we only wondered about. But thanks to huge advances in exoplanet studies, most spectacularly with the advent of NASA's Kepler spacecraft, we've learned so much about what's out there, including that:
  • somewhere between 80-100% of stars have planets or planetary system orbiting them,
  • approximately 20-25% of those systems have a planet in their star's "habitable zone," or the right location for liquid water to form on their surface,
  • and approximately 10-20% of those planets are Earth-like in size and mass.

So adding that all up, there are more than 10^22 potentially Earth-like planets out there in the Universe, with the right conditions for life on them.And even if you get there, how rare is a tool-using, technology-developing, rocket ship-launching species like a human? Complex reptiles, birds and mammals that could be considered intelligent by many metrics have been around for tens to hundreds of millions of years, but modern humans came about less than one million years ago, and we only became what we'd consider "technologically advanced" in the last century or two. Is there a 10% chance that if you make it through the previous step, you get to a spacefaring civilization? Or is that more like one-in-a-thousand, one-in-a-million, one-in-a-trillion or even worse?The truth of the matter is, this: we don't know. We know the Universe gives intelligent life a very large number of chances, on the order of 10^22. And we know that there's only a small probability of going from a chance at life to a spacefaring, technologically advanced civilization. What we don't know is whether that chance is something like 10^-3, 10^-20, 10^-50, or any number in between (or even worse). We know that life like humans arose once, at least, so the probability must be non-zero. But beyond that? We need data. And no amount of speculation or pronouncements will substitute for that information; we've got to find it to know. Anything else, despite what the New York Times claims, is nothing more than guesswork.

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