Why is it great that we haven’t seen aliens?

If you believe Hollywood, aliens coming to Earth could end in disaster: think Independence Day, or the aliens could come in peace: think E.T. However, the risk inherent in us not knowing what the intentions of an alien race might be is not what I am referring to when I say that it’s fantastic we haven’t seen aliens – and to explain why we’re going to have to zoom out a little bit.

Artist’s impression of the Milky Way. Image by NASA/JPL-Caltech/ESO/R. Hurt via ESO.

Chances for life

In our galaxy, the Milky Way, there are billions of stars, most quite similar to our Sun. Recent discoveries indicate that around each of those stars there are usually a few planets. On average it seems like each star having one earth-like planet is not unreasonable.

So we have billions of earth-like planets in our galaxy, and on each one there is a chance for life to emerge. We don’t have a great dataset for how quickly or easily life comes about (we only know of life evolving here on Earth!), but once Earth cooled, geological and archaeological records show that it didn’t take awfully long for simple life to start evolving.

Even if life is likely, intelligent (potentially space-faring) life is another question entirely. We know of zero life forms that are capable of exploring much further than the planet they started on… but that will change very soon, when we start jetting off to other stars. To understand what I mean by “very soon” we need to do a quick review of the history of everything.

Timeline from Wikipedia (version with clickable links here).

History of everything

The galaxy was formed about 10 billion years ago. Planets usually take a little bit longer to form, but records indicate that Earth formed about 4.5 billion years ago. The early stages of evolution are slow, with the first land-based life forms appearing only in the last billion years or so. When we think of the history of humankind we are really only talking about the last 50,000 years, where we went from cave art to agriculture to rockets. See Carl Sagan’s great take on this history in his original Cosmos series on YouTube.

Technological growth is fast, and it’s very easy to believe that the next 10,000 years could see us off this planet and exploring the galaxy. Ten thousand years sounds like a very long time to us, but for the galaxy it’s just a blink of the eye.

What does all this mean for aliens? Let’s say an alien species had a head-start on us humans, of say, a million years, a tiny little advantage in the history of the galaxy. Then, if they had any desire to leave their planet and explore the galaxy, they would have done so already, and be all across the sky – we would see them in their radio emissions, in any large structures they built, or even in person.

We don’t see any aliens.

A “little green man” alien is not something we have any (confirmed) evidence for, but why don’t we see any species at all? Source Beckie via Flickr.

Fermi’s Paradox

This paradox, why don’t we see any aliens when the probability seems so high, is called Fermi’s Paradox (after the guy who first made the argument) and there are a few ways to resolve it:

  • Maybe life is super rare and we are just a lucky fluke that is never to be repeated on another planet
  • Maybe aliens are very good at hiding, they have a Star Trek-like Prime Directive that says they must not interfere or reveal themselves to other civilizations
  • … or the last solution is that there is a great filter (or filters) wiping out all the aliens before they become galactic civilizations.

A great filter is some event, either they are brought about by the intelligent life: nuclear catastrophe, war, disease, or they are random: huge solar flare, giant meteors, etc. The first category humankind can, and has, protected ourselves from with good governance, empathy, and medicine… but the really scary options here are the completely random ones.

This is why it’s great for the long-term prospects of humankind that we haven’t seen or heard from aliens: it implies that all of the great filters are behind us! If there were any ahead of us we’d be able to see the remnants of the galactic space-faring aliens, and having some behind us (that we dodged through luck, or ingenuity) explains why we don’t see any aliens out there in the Milky Way.


4 Responses to “Why is it great that we haven’t seen aliens?”

  1. Julian Carlin says:

    @Gabriel, interesting! I have to admit I’ve never really thought about the idea applying on the small scale here on earth.

    @Umer, at a certain level we do have to throw up our hands and resort to the anthropic principle (https://en.wikipedia.org/wiki/Anthropic_principle), the best we can do is have good explanations for why we don’t see any others!

    @Yang, the possibility of having alien life at a similar level of technology as us is actually really small! If you think about the head start idea I proposed above then the chance that we’d be within ~100 years of each other in development seems super unlikely.

  2. Xuexiao Yang says:

    Interesting topic, Julian! Hope all the “great filters” will behind us forever, haha. I just imagine if there are some creatures which have
    a similar level of technologies with us but just living very far away from the Earth, this could be a mysterious question😄.

  3. Umer says:

    One thing that negates the notion that we have left behind the “Filters” is the question that “Why are we the only one’s (out of billion possibilities) to have those odds?” In my opinion this question is same as “Why are we the only life in the universe?”

  4. Gabriel Cornell says:

    The “great filter” you talk about is seen on a smaller scale, particularly when thinking about risks to endangered species. We may be doing really well at increasing the numbers of Pygmy Possum, for example, but if a huge fire (something that even we don’t have a lot of control over) swept through their prime habitat it is possible that they would be wiped out. The world (and universe??) is a cruel place.