When we think of looking for extra-terrestrial
life, we tend to focus on “earth-like” planets, that is, planets with conditions
that are similar to our own. “Life exists on earth,” the logic goes, “so earth-like
conditions are probably a good bet to find more life.” And yet. There are hundreds of billions of galaxies
in the observable universe, each with billions if not trillions of stars, and most stars
have planets orbiting them. That’s roughly a million billion billion planets. The enormity
of this number means it’s probably safe to assume that there are many many *many*
other planets with life – even intelligent life. And this, together with some basic physics
and fancy statistics, implies it’s more likely that species of intelligent extraterrestrials
will live on habitable planets unlike earth and will be unlike humans. More precisely,
they’ll be bigger than us and live in smaller groups on smaller planets. Now, I know it sounds crazy that with only
one data point – us – we can make any predictions at all about aliens we don’t
even know exist. But we can – here’s how: A basic result in statistics is that there’s
a big difference between the properties of a typical *individual* and the properties
of an individual in a typical *group*. The majority of humans, for example, live in countries
with a population of at least 180 million people. But the majority of countries have
populations of less than 6 million. And the majority of *religious* humans are
members of religions with more than a billion followers, while the majority of *religions*
have fewer than a million followers. And the majority of people who follow the
English Premier league are fans of teams with hundreds of millions of fans like Manchester
United, while most *teams* have just a few million fans each. It doesn’t matter how many individuals you
have, or how you make the groups – they can be religions, or fans of sports teams,
or the ingredients of this trail mix. It is a mathematical fact that the group that the
median individual belongs to will be at least as big/bigger than the median group. Or, simply
put, any time groups are not all the same size, most individuals will be members of
groups that are bigger than most of the other groups. The takeaway is that an individual should
expect to be a member of a large group, not an ordinary one. If you don’t know what
group you fall into (like, I don’t know what my blood type is), the most likely groups
to be in are the biggest ones – I’m probably O or A positive. And when it comes to intelligent life forms,
we humans don’t know what kind of group we fall into. So statistics tells us that
we, as individuals, should expect to be members of a large group of intelligent beings. That
is, we should expect that our species has a higher population than most other species.
And just knowing that we probably have a high population tells us a lot. For example, individual living beings require
space to live – I mean, the countries with the biggest populations tend to have large
land areas – so earth, with its high population, is probably bigger than most other planets
with intelligent life. Similarly, smaller living creatures need less
space and energy per creature, and accordingly tend to have higher population densities:
that’s why there are way more ants on earth than elephants. So humans, with our high population,
are probably physically smaller than most other species of intelligent life. In fact, we should expect to be abnormal among
intelligent aliens when it comes to anything that influences overall population size. Like,
easily available energy makes it easier to maintain higher populations, so we should
expect our sun to be somewhat hotter and brighter and closer than the stars of most intelligent
alien species; and we should expect our atmosphere to be more transparent to our star’s light;
and so on. If this all sounds a bit unspecific, well,
with just a few more simple and reasonable assumptions based on basic physics, we can
be more precise. Researchers have predicted that the population of most intelligent alien
species should be below 20 million individuals; the majority of planets with intelligent life
should have less than 80% the radius of the earth; and the individuals of most intelligent
alien species should be at least as massive as polar bears. So instead of looking for nearby intelligent
extraterrestrials on “earth-like planets”, the intelligent approach might be to look
for habitable planets slightly smaller, darker, and hazier than our own. In short, we should
expect to be the Manchester United of the universe, searching for AFC Wimbledon. Video source: https://www.youtube.com/watch?v=KRGca_Ya6OM
