Will We Ever Find Alien Life? - Script (Patreon)

The silence of the galaxy and the resulting Fermi Paradox has perplexed us for nearly 50 years. But our most recent surveys of the Milky Way finally allow us to draw scientific conclusions about the depressingly persistent absence of aliens.

When Enrico Fermi uttered the words, “Where is everybody?” he was succinctly summarizing what has become known as the Fermi paradox. In short: in a galaxy of hundreds of billions of stars, each of which having billions of years to spawn life and civilization, isn’t it odd that none have made themselves apparent to us. Enrico Fermi was, supposedly, using this as an argument against the plausibility of interstellar travel. If aliens can travel between the stars, why haven’t they visited? But the paradox is much broader than this.  There are several ways that an advanced civilization could give away their presence. Radio transmissions, robotic probes, or star-blotting solar arrays. A series of very recent surveys of our galaxy reveal none of the above, while at the same time proving the abundance of potentially habitable worlds. The Fermi paradox has become only more paradoxical, and these surveys are finally powerful enough to draw some serious conclusions about the rarity of advanced civilizations AND about the chance of us ever becoming one.

Before we get to that, let’s see what the state of the art in astronomical surveys is telling us. NASA’s Kepler telescope has discovered 2652 alien worlds to date – spotted as they marched across the face of their parent star in a chance transit alignment. This number allows us to figure out the fraction of stars have planets. Essentially all stars do. It also allowed us to figure out that there are something like 40 billion habitable planets in the Milky Way. By habitable, I mean rocky planets at the right distance from their star to have liquid water. TESS, the Transiting Exoplanet Survey Satellite is now in orbit and taking over from Kepler. It’ll find something like 20,000 new worlds, telling us once and for all how common Earth-like planets really are.

And how many of these planets have life? Uh, we have absolutely no idea. We have no way to even guess that yet. To answer this question we’ll need to look at the composition of their atmospheres. We talked about this before. Life is expected to massively alter the chemical composition of its home world’s atmosphere. We can’t see this effect on Earth-like planets yet, but the James Webb Space Telescope, to launch in a year … or so, will get close.

There’s a good chance we’ll have found hard evidence of extraterrestrial life in the next decade or so. But that’s regular old non-technological life. Surely a high-tech civilization would be easier to spot. We’ve been actively watching for radio transmission from other worlds for a half century. We’ve seen nothing. Even the famous WOW signal has likely been explained as emission from a pair of comets. That said, our search hasn’t even been sensitive enough to see human-level radio transmission in the nearest star system. We’re probably only sensitive to deliberate, beamed communications. Of which there are none.

But radio transmissions may not be our most likely first encounter with ET. Assuming any of those guys are like us at all, they’ll want to expand into and alter their galactic environment. And because they almost certainly have a head start on us of at least 1000s of years, that galactic gentrification might be visible to us.  You might remember Tabby’s star – the strange star in the Kepler field that showed these bizarre dips in brightness. Some very large collection of … something is passing in front of the star. Thrillingly, one proposed explanation was an alien megastructure - perhaps a vast fleet of solar collectors, built by the local inhabitants. Sadly this isn’t the case. Follow-up observations revealed that the wavelength-dependence of the dips is consistent with … dust. So likely natural space junk, not any type of artificial structure. As we like to say on space time, it’s never aliens.

Until it is. For example, these alien solar collectors may be our best shot at spotting other civilizations. An advanced civilization may launch so many solar satellites that it substantially blocks the light from its own star. Let’s call such a solar fleet a Dyson swarm – after the Dyson sphere, which is the next level up –a structure that completely encases a star. A Dyson swarm would cause an unusual dimming of its parent star and also cause an unusual increase in infrared light due to waste heat shed by the structure. These are things we can look for. 

Kepler saw none of this. But actually the best instrument for finding Dyson swarms is the European Space Agency’s Gaia mission. A team of astronomers scoured the Gaia data looking for stars that were unusually faint for their stellar type. They looked at 8,000 stars, and exactly one of those stars had a brightness significantly lower than expected. However they also figured out that the offending star has a binary companion, which may have caused a wobble in the star’s position, and that in turn may have messed with the star’s parallax distance determination and the determination of its power output. i.e. The star may just be further than expected, not wreathed in a swarm. But Gaia’s upcoming 3rd data release will expand this study from 8,000 to a million stars. If they’re out there we’ll find them. Eventually.

It’s still early days for our hunt for ET, but maybe we can at least agree that if there are any other technological civilizations in our neighborhood of the Milky Way they’re keeping to themselves. That still seems surprising given those 40 billion possible starting points for life in the Milky Way. After all, it would only take one of these worlds to spawn an expansionist species. Or even a single individual among that species to launch a single self-replicating probe. Give them a million-year lead on us – just one-ten-thousandth the age of the Milky Way – and SOMEONE should have colonized the galaxy by now.

Yet we see nothing. But detecting nothing is still data. Give astronomers data and they’ll write papers. A number of attempts have been made to address the Fermi paradox based on the new data. This is often done in terms of the famous Drake equation, which tries to estimate the number of communicative civilizations currently by combining a series of factors. There are astrophysical factors, like the rate of star formation and the fraction of these that form habitable worlds; biological factors, like the frequency of the appearance of simple life and the proportion of these that lead to intelligent life; and sociological factors, like the fraction of intelligent life that transmits radio signals, and how long that communicative civilization lasts.

The biological and sociological factors are so poorly understood that estimates of the number of civilizations vary between none to tens of thousands. But now that we have a much better understanding of the astrophysics factors, and are also pretty sure that there aren’t tens of thousands of advanced civilizations, we can actually start to constrain those biological and sociological factors. Astronomers Adam Frank and W.T Sullivan did this in 2015. They found as long as the odds of any given habitable planet spawning a technological species is greater than 1-in-60-billion, then humanity is not the first to appear in the Milky Way. Let’s go a bit further: assuming there aren’t 10s of thousands of civilizations before us, we must have beaten some steep odds – it must be harder than 1 in a million or so to go from damp rock to rocketship.

Luis Anchordoqui and collaborators found a less stringent limit on this likelihood by assuming that a lot of life gets wiped out by gamma ray bursts – a type of cataclysmically exploding star. We covered them before. These researchers estimate that, in order for us not to see any aliens, the chance of going from space rock to high-tech society must be less than a half a percent. That sounds high, but remember, it’s only for the planets NOT wiped clean by gamma ray burst.

Whether it’s gamma ray bursts or something else, our failure to find aliens tells us there must be a developmental bottleneck. Or, colloquially, a Great Filter, that seriously limits the Milky Way’s production of highly visible galactic civilizations. Optimists like to think humanity has already passed the great filter. That is, perhaps a biological factor of the Drake equation that keeps the number of aliens low. So watery planets may be abundant, but maybe there’s a step in the slow evolutionary crawl from primordial chemical soup to techno-monkey that makes advanced civilizations hellishly unlikely. This is something we can come back to – but you can look into the rare earth hypothesis or the Gaian bottleneck hypothesis for some plausible proposals.

If the great filter is behind us that’s good. It means we made it. It also means we have a long, lonely future as one of the galaxy’s only advanced species. But hey, one is better than none, right? But our modern understanding of the Fermi paradox permits a second interpretation. To wrap up, let’s consider the possibility that lots of planets produce civilizations at around our level, and they wipe themselves out with such thorough reliability that literally none ever leave a mark on the galaxy. Some scientists have been inspired by the persistent absence of evidence for aliens to investigate this possibility. Statistically, how likely is it that we wipe ourselves out?

Some scientists argue that deliberate annihilation of all humans isn’t just possible, it’s likely. Joshua Cooper and John Sotos point out that the technology needed to create an extinction-level event will inevitably fall into the hands of many  individuals. Over time, one wack-job … or impulse-control-challenged individual - will push the metaphorical big red button. These researchers focus on genetically engineered viruses, but the principle applies to anything doomsday tech – nuclear weapons, genocidal nanobots, willful or negligent environmental destruction, you name it. The researchers argue that all emerging technological civilizations will go through this phase of massive access to potentially cataclysmic technology. Depending on the destruction probability – let’s call it the “wacko factor”, you might expect civilizations to last from decades to thousands of years. But even thousands of years is brief enough to help explain the Fermi paradox.

That’s a nice sobering thought to end on. I should also point out that this same increasing access to technology may get humanity off the Earth and onto other planets. Which will come first? Spread human civilization across the galaxy or humanity's doom? I guess it depends on the relative probabilities – are we more inclined to acts of self-destruction and planetary sabotage, or to acts of preservation and exploration? Or perhaps more importantly – can we choose between these? Well we can sure try. The alternative may be eternal quiet across the lifeless reaches of space time.