The Fermi paradox - where are all the aliens?? Our observable universe is vast
with an estimated two trillion galaxies each containing anywhere from a few
million stars to billions of stars. Based on the only known observation of life in
the universe - our own - after an energy source liquid water is considered the
most important ingredient for life. The region around a star where water can
exist as a liquid on a planet is known as the habitable zone and the planets
within this region are known as habitable planets. The trillions of stars in our
observable universe contains trillions of habitable planets that orbit them and
this in turn means that there have been trillions of chances for life have
developed across the universe. And this leads us to ask, where is everyone?
During a discussion with a group of fellow scientists Enrico Fermi asked
that very same question and the lack of any evidence of any form of intelligent
extraterrestrial life along with the assumption that the universe should be
teeming with alien civilisations has come to be known as the Fermi paradox
The local group is a group of galaxies containing our own
Milky Way galaxy and a number of other galaxies and dwarf galaxies all bonded
together by gravity. Everything outside of our local group is unreachable to us
even if we were able to achieve light speed technology in the future.
This is because everything outside of our local group is speeding away from us
faster than the speed of light owing to the influence of a mysterious
dark energy. So instead of focusing on finding alien civilisations in the
universe, let's scale it down to not even the local group but down to just the
Milky Way galaxy. Some estimate that if advanced civilisations are able to build
spaceships that could sustain populations for generations to come
then these civilisations could colonise the entire galaxy
within two to ten million years.
In 1961 Dr Frank Drake came up
with the Drake Equation, a mathematical formula that attempts to use all the
factors we assume will come into play in estimating the number of active
communicative extraterrestrial civilisations in the Milky Way galaxy.
Let's go through each part of the equation one by one. N equals the number
of detectable civilisations that should be present in the Milky Way galaxy,
this is found by multiplying the following, R* which is the number of
stars formed each year. Fp which is a fraction of those stars with planetary
systems. Ne which is the number of planets per solar system with an
environment suitable for life. Fl which is a fraction of suitable planets on
which life actually appears. Fi which is a fraction of life-bearing planets on
which intelligent life emerges. Fc which is a fraction of civilisations that
develop a technology that releases detectable science of their existence
into space. L which is the length of time such civilisations release detectable
signals into space. Let's talk about inserting some numbers into this
equation and see what we are dealing with. Some claim that based on the lowest
estimates, the equation seems to indicate that it is highly improbable that we are
the only intelligent civilisation to exist in our galaxy. But the major
criticism is what we are presuming to be the lowest estimates. We only have one
example of life to work with, we are making presumptions on how likely it is
for life to develop, for intelligent life to emerge, for that intelligent life to
create advanced technology etc. all from our one known example. This leads us to
look at the Great Filter theory.
The Great Filter theory implies that one of
the steps between the formation of life to the colonisation of the galaxy must
be highly improbable. Let's chart four major steps in this
evolutionary path and look at them more closely:
Step one - Abiogenesis, the original evolution of life.
Step two - Development of complex multicellular reproductive life.
Step 3 - The leap to intelligence and Step 4 - colonisation of the galaxy.
Abiogenesis - we have no clear idea of how inanimate chemistry developed into biology, also as
far as we can tell, all living things in our world are related and we trace back
to only one origin of life. Does this mean that life is extremely rare, so rare
that it happens once in every galaxy or even so rare that it is a unique event.
That could very well explain why we have no indication that there are aliens out there.
Development of complex multicellular reproductive life.
Life may exist on a number of planets but for that life to have become complex
multicellular and reproductive means that a very specific set of conditions
must have existed or developed. Perhaps what has happened here on Earth is not
as commonplace as we imagine.
The leap to intelligence. We have plenty of
examples of life surrounding us on our planet but we humans are the only
intelligent life-forms that are looking to communicate with extraterrestrials.
It's highly unlikely that other planets would host aliens that are exactly like us.
So what is the probability that those
aliens would develop intelligence and the urge to communicate. Let's look at
the animals here on earth for example, are there any species that are likely to
develop intelligence similar to us? Is intelligence evolutionarily convergent?
Convergent evolution is the independent evolution of similar
features in species of where those traits were not present in their last
common ancestor, an example of convergent evolution is the eye in both cephalopods
such as squids and octopuses and vertebrates such as us.
Will evolution decide that intelligence is a similarly beneficial feature to all
creatures and in 100 to 200 years time can we expect crows and dolphins to
evolve a level of intelligence that bears any resemblance to our own?
We don't know, but if they did it would make the idea of intelligent aliens more likely.
Colonisation of the galaxy.
And finally we turn our attention to the
colonisation of the galaxy. All the other great filters are behind us but this one
may lay before us. Is there something that happens to all intelligent
civilisations - approaching the ability to develop technology that lets them travel
and colonise the galaxy - that sets them back or destroys them entirely?
Something like an asteroid colliding with the earth leading to mass extinction or
nuclear war or out of control climate change that makes the host planet uninhabitable.
Types of civilisations.
Civilisations are broadly categorised
into Type 1, Type 2 and Type 3 civilisations based on the amount of
energy a civilisation is able to use. This scaling system was first proposed by
Russian astrophysicist Nikolai Kardashev and it is known as a Kardashev scale.
A Type 1 civilisation can use and store all of the energy of its home planet.
A Type 2 civilisation can harness the total energy of his home planets parent
star, in our case this would be the ability to harness all the energy of the Sun.
The way to do this would be to use a Dyson Sphere,
a hypothetical device which would encompass the entire star and transfer
its energy to all the planets the civilisation has colonised.
And a Type 3 civilisation - also called a galactic civilisation - can control all the energy
of its entire host galaxy. Humans have not yet reached Type 1 civilisation
status and were estimated to become a Type 1 civilisation in a century or two,
but there's a huge leap between Type 1 and Type 3 and the great filter theory
which we have discussed earlier questions whether there is something
between the two that stops Type 1 civilisations from developing into a galactic civilisation.
Other solutions to the Fermi paradox.
There are a number of other potential solutions suggested for the Fermi paradox,
from the simple to the more fanciful and we'll explore some of them now.
Aliens have a more appealing virtual reality. Advanced alien civilisations may have
developed a virtual reality in which they prefer to spend their time, over
searching for other life forms in the universe.
We are uninteresting.
We are uninteresting to an advanced alien civilisation and while they may be aware
of us, they may not think that we are worth their time. They may view us the
way we view ants, interesting but not interesting enough to try and communicate with.
Communication problems.
Currently we are transmitting radio
signals in an attempt to connect with extraterrestrials but how likely is it
that they are using that exact same method of communication or that they can
even understand that form of communication. Perhaps we are too
different to even effectively communicate with advanced alien
life-forms anyway. We can't even communicate with most of the animals on
our planet so how can we expect to be able to do serve with extraterrestrials?
We may not be around at the exact same time. If advanced alien civilisations are
extremely rare we may not exist at the same time with the appropriate level of
technology on both sides to make contact. Or we may not even have been looking for long enough.
Simulation theory. We live in a simulation, a great matrix and we are
the only sentient beings programmed into this simulated universe. This begs the
question why the creators of the simulation decided to create such a huge
universe if all they wanted was for us to exist as the only intelligent
communicating life-forms in it.
Zoo hypothesis.
The zoo hypothesis imagines that an advanced alien civilisation is watching over us and
when the time is right they will make contact,
very much like the plot of the movie 2001 a Space Odyssey.
The super predator theory.
This theory imagines that an alien
civilisation has become a Type 3 civilisation that annihilates any future
civilisations that come close to attaining Type 2 or further capabilities
in order to remain the dominant civilisation in the universe. Or maybe an
even simpler explanation is the reason why we've not made contact with aliens
in that we are the first. We just happen to be the first intelligent civilisation
to have appeared in the galaxy. And that concludes our explanation of the Fermi
paradox and our exploration of some of the potential solutions to the paradox.
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