31 August 2019 | New Scientist | 43civilisations out there, then why haven’t we
seen signs of them already? This seeming
contradiction is sometimes called the Fermi
paradox, after Italian physicist Enrico Fermi,
who gave it its most succinct expression. With
a back-of-the-envelope calculation, he showed
that a single space-faring civilisation could
easily colonise a galaxy within a hundred
million years. Because the universe is
13.8 billion years old, and no interstellar
colonists have yet appeared on our horizon,
Fermi asked: where is everybody?
Radio silence
There are many proposed answers to this
question (see “Solutions to the Fermi paradox”,
page 44). Perhaps, say some, the aliens are
already here, just keeping their identities
secret. Perhaps they are deliberately steering
clear of Earth, treating it as a sort of cosmic
heritage site that deserves their protection.
Or alternatively, there are simply no aliens out
there. As an astrobiologist, I prefer to believe
that aliens are out there; we simply haven’t
communicated with them yet.
It isn’t hard to imagine why this could be the
case. Alien civilisations might well be millions
of years ahead of us in their technological
advancement. Trying to communicate with
them using our primitive technology would
be as absurd as teaching a ladybird to use a
telephone. That hasn’t stopped us trying, of
course, whether by including artefacts, such as
plaques etched with celestial maps and images
of humans, on our long-distance spacecraft or
by broadcasting targeted radio messages into
the depths of space. So far, no reply.
All hope is not lost. The Fermi paradox and
Drake equation specifically deal with the
question of intelligent life, with the ability to
communicate, travel and colonise. But only
a fraction of the life we know of would be
capable of these feats. Today, the vast majority
of Earth’s biosphere consists of microbes.
Single-celled organisms dominated the
planet’s surface for nearly 3 billion years
before multicellular life began. What is more,
microbial cells not only outnumber human
cells on our planet, they even outnumber them
on and in your body. If life exists elsewhere in
the universe, chances are it is microbial.
This means that the first detection of alien
life is unlikely to come from eavesdropping
on an interplanetary conversation. Instead,
we will need to scan the atmosphere of
other planets for familiar molecules that
primitive microbes are likely to emit: as
close as we can get to a fingerprint of life. >