Fermi Paradox: The Rare Earth hypothesis
In 1950, Enrico Fermi and some of his colleagues were having lunch at the Los Alamos National
Laboratory. Imagine them eating and chatting, maybe they were also drinking some wine, who
knows? The only thing that we know, and that everyone
knows, is that they had some conversations about UFOs.
In particular, Fermi issued a statement that would become quite famous. He asked: “Where
is everybody?”
Fermi was referring to extraterrestrial life. This question became the basis of the Fermi
Paradox.
Follow me in this video to get to know more about the Fermi Paradox and the so-called
Rare Earth solution!
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The Fermi paradox refers to the high probability estimates for the existence of extraterrestrial
intelligence (ETI) and the apparent lack of evidence. How is it possible, that, given
that the universe is infinite, given the huge number of stars and planets in the universe,
we still haven't found a signature of life other than us?
More than seventy years have passed since that lunch, and we still don't have a proper
answer to Fermi's question. As always happens, when we don't have answers we try to come
up with some theories. During all these years, many theories were
developed to explain why the “Great-Silence” endures. They are theories that could explain
why we seem to be alone in the universe. Some of them are optimistic, some others are
quite creepy and pessimistic.
For example, it could be that aliens are too far away for any contact, or maybe we are
the firs tones and we will be extinct before there are any others, who knows?
A creepy one could be the theory of hibernation. According to this completely speculative theory,
aliens would be hibernating and WAITING. But waiting for what?
Well, if a super-intelligent civilization had succeeded in replacing its biology with
machines, it might be waiting for the expansion of the universe to cool it down in order to
increase the efficiency of its computations. In fact, computers work better in colder environments!
However, among all these theories, in this video, we address the possibility that life-bearing
planets like Earth are just very rare.
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This hypothesis is known as the “Rare Earth Hypothesis”.
Basically, according to this hypothesis, life and the evolution of complexity require a
combination of astrophysical and geological conditions that are simply not common in our
Universe. In other words, we are quite special and unique.
If this hypothesis was true, we would be in a real messy situation.
Astronomy and mostly cosmology today assume the prevalence of intelligent life in our
universe because we think the Universe is isotropic.
For isotropy, we mean that the universe is the same in all directions, on a macroscopic
scale. You can understand isotropy thinking of a
sphere. If you are at the centre of this sphere, and you point towards different directions,
nothing changes. All of this It’s also consistent with the
Copernican Principle, which argues that if something is randomly-sampled, it is likely
to be representative of the majority. If we translate this in the astronomy and
cosmology field, the Copernican principle is telling us that Earth-like planets are
common in our Universe. We need such an assumption, we need the Copernican
principle because if the universe wasn't isotropic it would be very dangerous – and actually
almost impossible – to make quantitative studies of the objects we observe, such as
galaxies, stars and planets. We need it to set up our mathematical understanding
of the world.
If the Copernican principle doesn't hold, then Earth is actually not representative
of the whole and is in a class reserved for very few planets.
Maybe Earth is an outlier. Given the fact that we haven’t found any
evidence of extraterrestrial intelligence in the Universe yet, wouldn’t this seem
like the more plausible scenario?
The Rare Earth argument is based on two hypotheses. The first one is that microbial life is common
in planetary systems. The second one, states that advanced life
is rare in the Universe.
If we combine these two hypotheses, we understand that Earth-like planets may evolve from a
series of events and circumstances that are quite rare, making Earth a very special place.
This argument was in response to the inherent assumptions and biases that were identified
in the Drake Equation which essentially asserts that intelligent life should be plentiful.
For example, Ward and Brownlee, authors of the book on Rare Earth hypothesis wrote:
“The solution to the Drake Equation includes hidden assumptions that need to be examined.
Most important, it assumes that once life originates on a planet, it evolves toward
ever higher complexity, culminating on many planets in the development of culture. That
is certainly what happened on our Earth.”
They also say life originated here about 4 billion years ago and then evolved from single-celled
organisms to multicellular creatures with tissues and organs, climaxing in animals and
higher plants. And then ask themselves if this particular history of life—one of increasing
complexity to an animal grade of evolution—is an inevitable result of evolution or even
a common one. Maybe it could be just a rare combination!
Mathematically, the Drake equation can be expressed as a product of various factors.
N = R* X FP X NE X FL X FI X FC X L
N is the number of civilizations in our galaxy, R* is the average rate of star formation,
fp is the fraction of stars that have planets, ne is the number of planets that can support
life, fl is the number that will develop life, fi is the number that will develop intelligent
life, fc is the number advanced civilizations, and L is the length of time that these civilizations
would have to transmit their signals into space.
This equation aims to compute the number of civilizations in our galaxy. Of course, the
more we study and understand the universe, the more precise are our constraints on the
factors. For example, astronomers now estimate that
there are between 250 and 500 billion stars in our galaxy, which forms new stars at a
rate of about three Solar masses per year. The discovery of over 4000 extrasolar planets
in the past few decades has also allowed astronomers to get a much better sense of how many stars
have planets, and the number of planets that are likely to be habitable. In fact, based
on Kepler data, a study conducted in 2013 estimated that there could be as many 40 billion
Earth-sized planets orbiting in the habitable zones of their stars, 11 billion of which
would be orbiting Sun-like stars. Nevertheless, there is still a great deal
of uncertainty in the Drake Equation, especially when it comes to the emergence of life, the
rate at which life will give rise to intelligent life, and everything that follows.
But as we saif, Ward and Brownlee were sceptical about Drake's theory.
That's why they presented a new version of the equation in their book. It looks pretty
much like this:
N = N* X NE X FG X FP X FPM X FI X FC X FL X FM X FJ X FME
Here, N* is the number of stars in the Milky Way, ne is the average number of planets in
a star’s HZ,fg is the fraction of stars in the galactic HZ, fp is the fraction of
stars in the Milky Way with planets, fpm is the fraction of rocky planets, fi is the fraction
of habitable planets where microbial life arises, fc is the fraction of planets where
complex life evolves and there are a lot of other parameters that we have to take into
account if we want a good estimate of N. They even try to take into account the extinction
events that could happen during the evolution of an intelligent species.
Like the Drake equation factors, these are also subject to constraints and uncertainties,
but using Earth as a template and employing the Copernican Principle, it’s easy to see
how it would be difficult to find planets that meet all of the above-listed criteria.
Ward and Brownlee also listed other factors that were peculiar to Earth and are believed
to have contributed to the emergence and evolution of life.
For example, there’s the presence of plate tectonics which have been fundamental to climate
stability here on Earth.
And they also cited geological evidence that indicated that twice in our planet’s history,
the Earth was very cold and covered in ice. This is what astrophysicists call snowball
earth epochs. These epochs occurred roughly 2.2 billion
and 635 million years ago, both of which coincided with key developments in terrestrial life.
The latter Snowball period coincided with the Cambrian Explosion (ca. 570 and 530 million
years ago) which was characterized by a burst of species diversification and the appearance
of almost all animal lineages that exist today.
In other words, key events in the evolution of life on Earth appear to have followed a
Snowball Earth period.
So what can we say to conclude?
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In conclusion, we can say that like the Drake Equation, the Fermi Paradox, and all attempts
to resolve them, the Rare Earth Hypothesis is subject to uncertainty.
This has a simple explanation: we know of only one planet where life exists.
We can't develop a statistic, so we don't know if we will ever be able to get in touch
with other civilizations. Having only this one template severely limits
us when it comes to looking for life, which could exist in a range of environments and
chemical conditions. Life in the universe could be very different from life as we know
it!
But the amazing thing is that we only need to prove the existence of just one extraterrestrial
civilization in order to solve one of the biggest paradoxes of history, the Fermi Paradox.
Who knows, maybe it's just a matter of time and dedication. Maybe one day we will wake
up to the amazing news of a discovered alien civilization.
Meanwhile, we can just hope for the best, and keep it curious!
"This video ends here! Thanks for watching everyone! Do you think we will ever signatures
of an alien civilization? Let us know in the comments below, be sure to subscribe, and
I'll see you next time on the channel!"