A sample of reports related to extraterrestrial intelligence will give you two things: pseudoscientific accounts that aliens have visited Earth based on little to no evidence, and scientific searches with no sign of progress. It’s easy therefore to consign the idea of aliens to, if not quite the same folder as fairies, at least “hobbits” still surviving on Flores. That is, something that isn’t quite impossible but is so unlikely there is no reason to bother.
However, there are good reasons why money and brain power continue to be invested in SETI (the Search for Extra-Terrestrial Intelligence). Here are six of them:
Rocky planets like Earth are not rare
We have known for a long time that there are a phenomenal number of stars in the galaxy, now estimated at more than 100 billion, let alone in the universe as a whole. However, life (probably) requires planets, not just stars. At one point, it was thought planets only formed under very rare circumstances – another star passing a developing system at just the right time – which would have cast serious doubt over the prospects for life elsewhere.
Even once the current model for planetary systems became dominant, questions remained. Perhaps planets, or at least Earth-like planets, were very rare for some reason we hadn’t identified.
However, the abundance of data from the Kepler and TESS telescopes, backed up by other methods of planet detection, reveals that rocky planets are very common indeed. Some systems have at least seven, and possibly more are waiting to be found. Most of the rocky planets we have found so far are too close to their stars to be ideal candidates, but that’s only because planets in those locations are easier to find. The longer we search, the better prospects we find. It’s clear our galaxy is teaming with places where life could exist, and the same is almost certainly true in other galaxies, and possibly globular clusters, as well.
Even if only one in a billion end up inhabited by someone capable of building a spaceship, that still means we’re not alone.
Life’s early start on Earth
We still don’t know exactly how life started on Earth, even if we’ve found a few steps in the chain. Consequently, it’s technically possible the existence of life is a freakish event that has happened so seldom it’s never led to another species capable of advanced technology.
Nevertheless, we know that life got started on Earth very early, possibly about as early as it could without being walloped by space rocks so big they make the dino-killer look puny. It’s been compared to buying a weekly ticket in a lottery where you don’t know the odds (although why you would do is beyond us). If you win on the first draw, you might just be very, very lucky, but it’s more likely the odds just weren’t that long.
If it wasn’t so hard for life to evolve here, it shouldn’t be harder on many similar planets.
Life finds a way under such extreme conditions on Earth
Once life does evolve, it has an astonishing capacity to occupy some truly foreboding niches. From the heat and pressure around (and beneath) hydrothermal vents, to the freezing cold of Antarctica, the dryness of the Atacama, and the hyper-salinity of some desert pools, even in conditions that kill 99.99 percent of life on Earth, something manages to make its home.
There’s no reason to think extraterrestrial life would be any less resilient. In which case, the prospects for life both evolving – and flourishing – elsewhere seem particularly good. Life may have no inbuilt tendency to progress towards intelligence, but the more diversity exists, the higher the chance some will eventually get smart.
It’s not that surprising we haven’t found the signs of life
We’ve been looking for signs of life on other worlds longer than most readers have been alive. This has led some people to reverse the lottery analogy used above. If you enter a lottery long enough and don’t win, you might not just be unlucky; maybe the chances are very small, or the game may even be rigged.
The problem with that conclusion is that we really have not looked that hard. Most of our efforts to find life outside the solar system would only work if aliens were either very, very nearby (on cosmic scales), were advertising their presence very loudly, or were sending messages straight at us. There’s no reason to expect any of these things to be true, even if there are a great many advanced civilizations already in existence.
Techniques capable of detecting more modest signals, or picking them up at greater distances, only started last year. Unless we expect to find societies at least as advanced as us on almost every habitable rock, there’s just no reason to expect to have found anything yet.
We may be using the wrong techniques to look
There’s also the question of whether we’ve even got our methods right. It’s possible the universe is abuzz with intelligent chatter, and we’re just not tuned into the right frequency (metaphorically, but perhaps also literally). Our searches for alien communication are reminiscent of the proverbial drunk looking for their keys under a streetlamp because the light is better there.
We’re doing a little better than the character in that story, who famously knew he’d dropped his keys elsewhere, but couldn’t be bothered hunting in the dark. In our case, the radio frequencies that have been the focus of our search for alien chatter have been picked in part because they make some sense. However, it’s also true that we’ve mostly looked in ways that are cheap and (relatively) easy. If highly advanced species communicate between worlds using lasers, or something we can’t yet imagine, we’d have no way of tapping in just yet.
Expectations of space travel are based on quite dubious assumptions
When Fermi constructed his famous paradox, he wondered why the aliens were not visiting us already. We still don’t know, but in the time since, people have come up with a great many explanations, some quite plausible, and only a few of these require there to be no aliens.
Put simply, space is big. Sailing across the Atlantic was once seen as an epic voyage, but that only took nine weeks, even with the rickety ships that first made it. Unless there is a way around the light barrier, space travel is orders of magnitude longer, as well as more expensive. The assumption that pretty much as soon as anyone invents space flight they’ll be colonizing the galaxy, is based on confidence about alien psychology that has little basis. It may be that interstellar travel is so expensive, it’s only done in extreme situations, and many places are left in peace.
Addendum on “belief”
Whenever the words “belief” or “believe” get used in a popular science article, some may want to rubbish the terms, deeming it incompatible with evidence, particularly on a topic like this. We put believe in our headline because when it’s used in conversation, it’s with a more nuanced meaning. On the available evidence, it makes sense to believe alien species at least as advanced as us are likely to exist in the galaxy. It does not, however, make sense to believe they’re regularly buzzing Earth and abducting travelers, or that they built the pyramids before heading off and taking their technology with them.