Are we wrong about aliens?

Photo by Alex Andrews from Pexels

In a previous post, I discussed why life in the universe should be incredibly common. The only problem is that it isn’t. Or at least, it doesn’t seem to be. So maybe we got something wrong?

Who is to say the Earth is typical? Or that life tends to appear on planets like Earth? Maybe we are a cosmic accident in an otherwise desolate and lifeless universe?

The problem is, it’s not a good idea to imagine we’re special.

Cosmology — the study of the universe itself — is specifically built on us not taking a privileged vantage point. For us to apply our laws of physics to the whole of reality, we rely on the fact that whatever happens here applies, broadly speaking, everywhere else too.

It’s a somewhat philosophical argument, because we cannot empirically verify that some distant region of space has slightly different physics. Equally, it’s difficult for us to imagine a scenario where life is unique and we have instead assumed one of the majority vantage points of, well, not being alive. Hence, whilst this law of mediocrity is a helpful scientific tool, it’s not foolproof.

Nevertheless, let’s take a fine tooth comb to the process by which a lump of rock turns into a lump of rock with creatures that like ice cream and blog posts, to see if there are any problems with our conclusion that aliens should be everywhere.

Firstly, in our original argument we stated there are lots of planets out there. Is that really true?

Yes. Yes it is.

As of the start of this year, there have been almost 5000 confirmed exoplanet discoveries. This number seems small, but it represents the number we have discovered in the last thirty years. Remember, planets don’t tend to emit light like stars. They’re both far away and very difficult to spot.

According to NASA, since the 1990s the number of known exoplanets has doubled approximately every 27 months. In some cases, multiple planets have been found orbiting a star.

In fact, we can be more specific about our planetary estimate. It’s believed that one in five sun-like stars have an Earth-sized planet, leading us to think there could be 11 billion habitable Earth sized planets in the Milky Way alone.

And this is with a healthy dose of human-centric bias. If planets can exist around red-dwarves this number increases to 40 billion and even greater numbers if we include planets that are not Earth-like, or that are moons, or that have internal sources of energy that don’t require stars. Who’s to say that life can’t exist in gas clouds too?

The number of possibilities might massively exceed 40 billion and that’s just for our galaxy, which makes up a cluster which, in turn, makes up a supercluster. And there are millions of superclusters in the observable universe.

In other words, yes. There are a lot of opportunities for life. But how many opportunities become reality?

We know that Earth is about 4.5 billion years old, and that life emerged about 3.7 billion years ago. This is a tiny fraction of our home’s lifespan, and even smaller when you consider that Earth was subjected to a heavy bombardment of asteroids leading to temperatures that prevented the formation of complex molecules for a significant period of its early life.

Given the first stars formed only a few 100 million years after the big bang — which was 14 billion years ago — there has been more than enough time for a few intelligent species to get a head start over humans.

So, we have the time. What else do we need for life?

Well, we’re made of water, so Hydrogen and Oxygen. We’re Carbon based and use a lot of Nitrogen too. As it turns out Hydrogen, Oxygen, Carbon, and Nitrogen are the first, third, fourth and seventh most common elements in the universe respectively. Which is convenient. (Incidentally, silicon is eighth and speculated as an alternative to carbon for creating life).

In isolation, elements are not that special, however the famous Miller-Urey experiment found that under very simple conditions on Earth, it was possible to create amino acids — the fundamental building blocks of life — in a few days, with just a spark of electricity and some heat.

So not only are the elements abundant, but the process to turn them into the constituents for life is extremely simple and plausible.

So, life is very likely to form but who’s to say it’d be intelligent? Dinosaurs were around for 300 million years — far longer than modern humans — and would have likely continued for a while longer without a meteor ruining all the Jurassic fun. Intelligence is not necessarily important for life.

Here is perhaps the weakest link in the chain from lump of rock to humankind. Maybe the level of intelligence seen in humans is something uncommon. However, perhaps we need to invoke the law of mediocrity once again.

There are billions of opportunities for life in our galaxy. All we need is a species that are a few million years ahead of us or slightly more intelligent. That only needs to successfully happen once for us to see evidence.

To give us credit, we’ve built rockets that take us to the Moon and probes that have left the Solar System. We’re closer than we think to travelling to other stars. Mediocrity might allow us to place ourselves directly at the centre of the intelligence distribution, with plenty of aliens above us who have perfected interstellar travel and those who are still figuring out farming.

However, in thinking about our perfectly average civilisation, we’re making an assumption about our future trajectory. We haven’t achieved interstellar travel, and who’s to say we ever will?

How can we extrapolate to aliens when we don’t even have one datapoint to compare against? Perhaps we should be wary of generalising our future course. In fact, maybe the absence of aliens means we should extrapolate backwards:

If aliens haven’t managed interstellar travel, then perhaps we will not either.

After all, we have rockets to take us to space but also rockets to carry nuclear weapons. It doesn’t take a huge leap of faith to think that the argument we’ve been using to justify life everywhere might apply to why we don’t see it anywhere.

The absence of advanced civilisations could be a warning.

Maybe every species that has been and gone has done something that we will do at some point in our future. A hard limit at the final step to intergalactic colonisation.

This leads us to the great filter. The mysterious process preventing interstellar life. Perhaps the filter represents the end of civilisation. Or perhaps it’s something else.



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