Fermi Paradox - there is only us in the Galaxy!
As Arthur C. Clarke said, "There are two possibilities:
either we are alone in the universe or we are not. Both are equally terrifying."
The Italian physicist Enrico Fermi went even further, making our minds almost
certain that the first hypothesis is much more probable than the other...
Roll intro
Among his other merits, the Nobel Prize winner Enrico Fermi was esteemed for his
extraordinary ability to go straight to the heart of a problem and then
be able to describe it in its real essence. Impressive was his way to estimate the order
of magnitude of a numerical value related to a given phenomenon from almost nothing (often by
performing complex calculations in his mind). Fermi tried to impress this ability on his
students, so much so that he used to ask, without warning, seemingly unanswered questions. How many
grains of sand are there on the world's beaches? How far can a crow fly without
stopping? How many atoms of Caesar's last breath do we inhale every time we fill our
lungs? How many piano tuners are there in Chicago? These "Fermi questions" forced students to propose
rough estimates drawing on their knowledge of the world and their daily experience,
rather than on theoretical or prior knowledge. One day in the summer of 1950 Fermi was in
Los Alamos in the company of colleagues such as Edward Teller, Herbert York and Emi Konopinsky.
Together they walked to a nearby restaurant amiably discussing the
recent spate of "flying saucer" sightings that had spread across the country.
After a few jokes the conversation turned serious and the four colleagues wondered whether or not
the flying saucers could exceed the speed of light. Fermi asked Teller what he thought was
the probability of having confirmation of the possibility of superluminal travel by
1960. His friend's answer, one chance in a million, did not convince him: it was too
low. According to him it was closer to one in ten. The four sat down at the table and the talk turned
to lighter topics. Then, in the middle of the conversation and as if it had rained down from the
sky, Fermi asked: "But then, where is everyone?". His diners immediately understood that he was
still referring to the issue of extraterrestrial visitors. And since it was Fermi who was speaking,
they realized that the question was more complex and profound than it first seemed.
York recalls that Fermi made a series of quick calculations and concluded that if
aliens really existed we should have been visited a long time ago, and more than once.
A result that immediately answered his question: there are no extraterrestrial
intelligences in this galaxy (and perhaps in the entire universe), we are alone!
And if you don't like the idea, let's at least try to think about it a bit. Let's put aside the
billions of galaxies in the universe, each of which is home to trillions of planets,
and focus only on our galaxy: the Milky Way. The number of planets that compose it is around
100 billion, of these - even if the estimates vary a lot and the detailed list is much more
concise - about one billion are potentially habitable. If even 0.1% hosted some form of
life, we would still be talking about a million planets inhabited by aliens (from
the little green men of the collective imagination to some modest bacterium).
So how is it that we don't find anyone? As we know, this is the heart of the Fermi paradox:
we are surrounded by billions of planets that host life forms,
but we have never crossed them. Not only that: no extraterrestrial has ever even found us.
It is a question of logic: homo sapiens, for the times of the universe, is a very
recent species. Which makes it plausible that, elsewhere, there’s some species technologically
superior to our. And since we are looking for other forms of life, it is plausible that others
have already done so and are still doing it. So why doesn't anyone send us any signals?
All our knowledge of terrestrial life indicates that life has a natural tendency
to expand throughout the space available to it. Why should extraterrestrial life behave
differently? A technologically advanced alien civilization could colonize the Galaxy in a
few million years. So it should already be here! The Galaxy should be teeming with life!
The reason for this belief is very simple ... If one of these civilizations sent colonizing
spaceships to nearby stars at a speed equal to one-tenth the speed of light (0.1c) and if
the colonies in turn sent their ships, that civilization should be able to colonize the
Galaxy in a very negligible time compared to the age of the universe. If the ships did not take
breaks between the different voyages, there would be a wave of colonization that spreads through
the Galaxy at a speed of 0.1 c. If the interval between voyages were instead as long as the voyage
itself (after all, travelers need to settle on the planet they just landed on before setting off
other ships), the wave would move at 0.05 c: so it could travel from one end of the Galaxy to the
other in a time ranging from 0.6 to 1.2 million years. To simplify the discussion, we can assume
that it takes a million years to colonize the Galaxy. A million years is a long period on a
personal level and it is also long at the level of an entire species, but it is nothing compared
to the total time available for colonization. Yet, as far as we can know so far, there is no trace of
these colonizers. And in the face of this bitter observation, all that remains is to take note of
our uniqueness as a sentient animal species. In reality, these arguments are played
on the opposition of two concepts always in conflict with each other,
called "hypothesis of the rarity of the Earth" and "hypothesis of the principle of mediocrity".
The hypothesis of the rarity of the Earth argues that the emergence of life on our planet required
an extremely unlikely combination of astrophysical and geological events and circumstances.
This hypothesis is opposed to the principle of mediocrity (an extension of the Copernican
principle), that the Earth would be just a typical rocky planet in a typical planetary system,
located in a non-special region of a large but common spiral galaxy.
Stephen Hawking himself stated one day that "we are nothing more than an advanced species of apes
on a planet less than a mediocre star": a vision that is very different from the exceptionality
with which man has always looked at himself. But not all experts think like the recently
deceased astrophysicist: the director of the Columbia Astrobiological Center,
Caleb Scharf, overturned Hawking's thesis in his 2014 book (The Copernicus Complex),
showing how the Sun, in truth, it is not at all mediocre and how much the architecture of
our solar system is very particular. A similar thesis was supported by
astrophysicist John Gribbin in his essay Alone in the Universe. According to Gribbin, life on Earth
was made possible by a chain of extremely unlikely coincidences. Starting with the fact that it took
four billion years for life on Earth to pass from the primordial soup to the first multicellular
forms: an incredibly long and complex process (the entire universe is 13.8 billion years),
during which thousands of things could have gone wrong and instead led “miraculously” to
the incredible variety of life we ​​know today. In short, our planet would have nothing "mediocre"
at all ... indeed, it could even be the only one in which the entire evolutionary process has ended
up generating sentient beings capable of reasoning about themselves and understanding the universe.
Do you want proof? Here is a list of some of the necessary conditions that within a
few billion years have allowed the Earth to fill with life and you to be here watching this video:
A single star to orbit around. Binary or multiple star systems would give rise to
planets with chaotic or unstable orbits. An "ordered" planetary system. There can
be no planets of great mass in very elliptical or closely spaced orbits (a very frequent situation
in the case of exoplanets known today), capable of destabilizing the set of orbits.
A “clean” interplanetary environment. There can be no excess of orbiting solid matter because
collisions would be too frequent and destructive. A second generation parent star. These stars,
like our Sun, were formed by incorporating the heavy metals released by the explosion
of older stars. Without metals in the core of our planet, the "dynamo" capable of forming
the magnetic shield that allows the Earth to defend itself from cosmic rays and the
solar wind would not have been activated. Adequate mass. A low-mass planet could not
hold back its atmosphere, which, like Mars, would be dispersed into space.
The existence of plate tectonics. Some researchers believe that without the movement of continents
life would not have evolved into complex forms. The continual shuffling of the Earth's mantle
allows methane and other compounds to escape through thermal springs on the ocean floor, which
would otherwise be sterile. Tectonic activity also plays an essential role in maintaining the
long-term stability of the Earth's thermostat. Let us consider the case of carbon dioxide. A planet
with too much carbon dioxide could end up like Venus, a planetary blast furnace. The activity of
the plates on Earth helps to regulate their level. The presence of the Moon. Without the Moon, life
on Earth could never have reached too high a level of complexity. Our planet would have been a very,
very different place. Without the Moon to slow down, an Earth day would only last 8-10 h. The
faster rotation would have produced winds of 160-200 km / h. The inclination of the Earth's
axis would have oscillated by as much as 90 °, causing extreme variations in temperature
over thousands or millions of years (which is what happened to Mars, without a sufficiently
large moon). And although our seas would still have had tides, these would have been smaller,
produced only by the Sun, and they would not have been able to continually stir the seabed
ensuring the necessary exchange of oxygen and nutrients. And finally, if we had not been enticed
by the presence of an affordable goal, close enough to be reached in a few days of travel,
and sufficiently "hospitable" to allow humans to walk on it, what future would space exploration
have? Would we have invested equally as much in the technology and skills that led to the
creation of a space station where men and women can live for months, and to human exploration
projects of Mars and other remote places in the solar system? Without the Apollo missions,
we would not have all the information we now have on our satellite, but above all
perhaps the stimulus and enthusiasm to begin the conquest of deep space would have been lacking.
But these that we have briefly listed are just some of the requisites necessary for
the emergence of an intelligent and technological civilization.
Probably, in the absence of even one of these characteristics,
our Earth would now contain only traces of primordial life ... Which leads us to think
that for us it was like winning a large lottery for a considerable number of consecutive times.
How many in our galaxy could have had the same luck as us? Maybe nobody else.
The famous French biologist Jacques Monod wrote one day that "Man finally knows he
is alone in the indifferent immensity of the universe, from which he was born by chance".
It is a rather melancholy thought. But sadder still is the thought that the possibility
offered to us by chance could be badly wasted. If we survive, we will have a galaxy to explore
and make ours. If we destroy ourselves, if we ruin our home planet before we're
ready to leave it... well it could be a long, long time before an individual of
another species looks up at their planet's night sky and wonders: "Where is everyone?"