As humans begin to travel to places beyond Earth it’s possible we may encounter new forms of life. In fact branching out may not be necessary, as they may eventually come to us. While the existence of extraterrestrial life is far from certain, discovering such a thing would definitely be a momentous milestone in the history of our species. The possibility of other intelligent life out there is especially fascinating. But even finding some alien microorganism, however rudimentary, would be a game changer. Such a thing would prove that Earth is not unique, and that the galaxy is probably filled with life. And this, in turn, would greatly increase the odds that intelligent life exists elsewhere.
Because so many UFO sightings and alien abduction stories turn out to be bogus, or at least suspicious, there’s an unfortunate tendency to place the notion of intelligent life beyond Earth in the same category as ghosts, ESP, magic, and the like. But unlike these things, which run counter to basic scientific principles, extraterrestrial life does not. In fact, many scientists believe intelligent life should exist elsewhere in the universe. While there are still some gaps in our understanding of how life emerged on Earth, there’s a lot we do know. And there doesn’t seem to be anything about that process that couldn’t happen on other planets.
The Earth formed about 4.5 billion years ago, at a time when the universe itself was already 9.3 billion years old. For its first 600 million years, roughly, our planet was lifeless. Then something happened. Certain chemical reactions occurring in the water transitioned to something more biological. Organic molecules began to replicate, and with replication comes evolution by natural selection: better replicators make more copies of themselves than poorer replicators. For the first couple billion years of life on Earth only single-celled organisms lurked in the sea. Gradually more complex creatures began to emerge, until, quite suddenly, animals evolved during the Cambrian Explosion about half a billion years ago. Our species, Homo sapiens, probably evolved about 150,000 years ago, but only reached our current level of intelligence in the last 70,000 years.
It seems like we humans owe our existence to at least three lucky historical accidents. The first was the emergence of any sort of life on Earth. The leap from organic molecules to organisms is probably the most mysterious step in the history of life on Earth, and it’s possible that it was an extremely unlikely event. The second barrier was the development of multicellular life. It perhaps took longer for multicellular life to appear on Earth than life itself, which suggests this event may also have been improbable. But while life evolved (as far as we know) only once on Earth, multicellular organisms have evolved at least a couple dozen times. So maybe once a planet has life it’s bound to become more complex, however slowly. The third difficult barrier that needed to be crossed, humanity’s hat trick, was to evolve intelligent brains. This allowed us to begin speaking about abstract concepts, write, create laws, preserve history, etc. Of all the millions of species that have evolved we are the only ones that have pulled this off. So a hypothetical alien intelligence would perhaps also have needed to beat the odds three times. But just how hard are those odds to beat?
The famous Drake equation calculates the number of intelligent civilizations in our galaxy that we could theoretically communicate with. It takes into account factors like the age and size of the galaxy, the number of planets in it that may harbor life, how likely those lifeforms are to develop into complex civilizations, and, critically, how long those civilizations last. The down side of the equation is that it is quite sensitive to the values we use for each of its seven variables, and depending on the assumptions one makes about any one of them it can make drastically different predictions. By some estimates the number of other intelligent civilizations in the Milky Way is less than one. In other words we on Earth have already beaten the odds and are most likely alone in the galaxy. If we use slightly different--but still reasonable--values for a couple of the Drake equation variables it predicts several million other technologically advanced civilizations!
There’s a well known story that took place over lunch among scientists working on the Manhattan Project, in New Mexico in the early 1940s. The topics of these lunchtime conversations were predictably nerdy given the caliber of the minds gathered there, and one thing they sometimes discussed was the probability of intelligent life existing elsewhere in the galaxy. One day the physicist Enrico Fermi blurted out something along the lines of, “So where are they?” Others at the table apparently laughed, since although they had not been talking about it just then they all knew he was referring to alien life. The Fermi Paradox is what we now call the apparent contradiction between the likelihood of alien life and our inability to detect them.
Since we know that life emerged on at least one planet in our galaxy, it makes sense to look to similar planets for extraterrestrial life. According to a recent estimate there could be as many as six billion Earth-like planets in the Milky Way. That is, Earth-sized rocky planets orbiting within the “habitable zone” (capable of surface liquid water) of a Sun-like star. Think about the number six billion for a moment. Even if the odds of life appearing on a planet like Earth are as low as one in a million, we should still expect life to have appeared on another 6000 planets. But why assume such long odds? It’s true we haven’t yet found life outside of Earth, which may hint at its improbability. However, our efforts to look for life have thus far been fairly limited. Traveling to new moons and planets could change that.
So if we do find life elsewhere in the galaxy what will it look like? Will it be so different from anything on Earth that we’ll have a hard time even comprehending it? Maybe. Given the variety of lifeforms on our own planet it could be that creatures unrestrained by the conditions on Earth would be strange beyond imagining. But then again maybe not. There’s a reason, after all, that we label these six billion other planets “Earthlike”. Moreover, such planets would be constrained by the same laws of chemistry and physics that exist on Earth, and, just as importantly, by the same laws of evolution. An intelligent alien life form would have evolved from something simpler, just like we humans did. An intelligent being on one of these planets probably evolved under similar environmental pressures. We know from life on Earth that different creatures in the same environment can undergo convergent evolution. This means that as a general principle, similar environments will tend to harbor similar life forms. Of course, a species’ ecological niche, as well as purely random factors, are also important in determining its characteristics. Nevertheless, it wouldn’t be unreasonable to expect an alien intelligence to share some physical characteristics with human beings. Perhaps Star Trek and Star Wars aren’t that far off in their depictions.
In the event that intelligent beings exist elsewhere in the galaxy, it would be an improbable coincidence for their civilization to be at the same level of development as ours. Much more likely they would far more technologically advanced than humanity. If we make contact with such a civilization, and if we're friendly to each other--perhaps a big if--what could we learn from them? What sorts of things would an ultra-advanced species have already mastered? Could we be taught the secrets of interstellar travel? Of longevity, superintelligence, or even happiness? These kinds of questions are very speculative, but fun to consider.
Comments