universe alien life

Is there alien life?

If the Universe is teeming with aliens then where is everybody? It’s one of the biggest conundrums in the Universe, known as the Fermi Paradox. That means that if the Universe is so conducive to life, and if there are so many opportunities for it within our galaxy alone, why isn’t there any evidence (outside of the History Channel of extraterrestrial life?


Life and intelligence

universe molecule

Self-replicating complex molecule

After all, given the fact that the universe is nearly 14 billion years old, while our galaxy itself is only a hundred-thousand light years from end-to-end, shouldn’t all of the potentially habitable planets have been visited, and colonized, by now? There are good news and bad news.

The good news is we’re here! That means we have at least example in the Universe where things worked out in favor of intelligent life. As far as we can tell, this means the following things have happened:

  • A star was born with a planet that orbits it at the right distance for it to be potentially habitable.
  • That planet had the right mix of elements on it, particularly carbon, nitrogen, oxygen, hydrogen and phosphorus, in order to create life-as-we-know-it.
  • Life actually begun, at some point. This means, at the very least, a self-replicating complex molecule found a way to replicate itself. (The “information-encoded” clause distinguishes DNA/RNA-based life from, say, a non-living crystal.)
  • Life succeeded for a long enough time that it evolved not only beyond this simple, primitive state, but into complex, multi-cellular, highly differentiated organisms.
  • At least one of these organisms developed what we consider “intelligence” to be, and used it to learn about their environment.
  • Eventually, before going extinct, these organisms managed to leave their own world, and set out to explore, and possibly colonize and/or inhabit some of the other ones in our galaxy.

Now, there’s no doubt that all but the above-mentioned last step has already happened here on Earth. And there are huge contingents of our society striving to achieve that last one.


But the big question is this:

alien civilizations

Should there really be tens-of-thousands of civilizations just like us?

How common should this occurrence actually be? Should there really be tens-of-thousands of civilizations just like us, or even more advanced, out there right now, in our galaxy alone? Or are we the only ones like us, in the entire history of the observable Universe, who’ve ever existed? Of course, we don’t know. But the fact of the matter is this: we have no right to expect that just because it happened once, here, that any of these steps are at all common! Thankfully, we do have some evidence to tell us that some of the things that happened are, in fact, common.


The stars, for example.

universe star planets

Twenty percent of the stars in our galaxy have planets within their habitable zones

We know there are somewhere between about 200 billion and 400 billion stars in our galaxy. The vast majority of them, about 95 percent, live as long or longer than our Sun. This means that they do have, at least potentially, plenty of time for evolution to take place. And we’ve also learned, through our exoplanet hunts, that perhaps as many as 20 percent of the stars in our galaxy have planets within their habitable zones. In other words, we’re quite confident that, within our galaxy alone, there are literally billions of stars with rocky planets orbiting at the right distance for life to exist, and they’re loaded up with the right kinds and amounts of elements to possibly give rise to life.


The development part is another great unknown.

evolution

How likely or rare is the evolution of a human-level of intelligence?

For nearly 3 billion years, life on Earth was no more complex than single-celled, asexually reproducing organisms. Yes, this includes some extraordinary one-celled creatures, like corals and sponges, but still single-celled organisms, nonetheless. But at some point, evolution permitted complex, highly differentiated, multicellular animals to arise. Is that a commonplace occurrence in the Universe? Or is that an extraordinary rarity? Again, we have no quantitative information except this one instance here on Earth. Until we do, we’re really just playing a guess-timation game.

Finally, here we are! The most intelligent species, as far as we know, ever to exist! Even given the existence of life and the evolution of highly complex, highly differentiated creatures, how likely or rare is the evolution of a human-level of intelligence? Our brain-to-body-size ratio dwarfs that of our nearest competitor, the dolphin, by nearly a factor of two, and the next-nearest great ape by a factor of about three. A chimpanzee society might not have the intelligence to understand or explore the Universe, but we certainly are capable! How rare is this level of intelligence? As far as we know, we’re the only species to attain it in the history of Earth, and we have no idea how common this is in the Universe. It could be extremely common, or we could be the only ones.


And finally, what about spacefaring civilizations?

universe colonization

What about the colonization of other worlds?

What about the colonization of other worlds? The fact that we haven’t either contacted or been contacted by another species very likely tells us that all of these things haven’t happened abundantly in our galaxy, but how rare or common is it? The evidence, at this point, points to, at best, not that common. (And, at worst, we might be the first-and-only, and even that’s only if we can get our act together!) But the fact of the matter is, I’ve never thought of the Fermi paradox as very much of a paradox. It’s not at all hard to imagine that the answer to, “Where is everybody?” is that there isn’t anybody else.

If the answer turns out to be that there isn’t anyone else, it’s up to humanity to change that. And if there is somebody else… well, I want to know! Don’t you?


scienceblogs


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