The Great Silence — Are we alone?
“Humans went from not being capable of flying to become explorers of the solar system in less than 100 years. Considering how old is the universe, where is everyone?”
The following is an excerpt from my upcoming book “A Story of More Than 5000 Worlds: An Insight Into The Possibility of Life Beyond Earth”.
One of the main points of the detractors of the Search for Extraterrestrial Intelligence (SETI) initiatives is that we have been looking for signals for more than 60 years and nothing has been found so far. This argument, however, doesn’t take into account the vastness of the universe, and how little we have actually searched.
The universe is so big that we have only searched a portion “Similar to the ratio of the volume of a large hot tub or small swimming pool to that of the Earth’s oceans”[1]
Regardless, if life is common out there, we should have heard from someone already.
Humans went from not being capable of flying to become explorers of the solar system in less than 100 years. Considering how old is the universe, and some estimations that some Earth-like planets could be at least 2 billion older than Earth[2], we should have heard by now of any hypothetical extraterrestrial civilization that has the means of achieving interstellar travel.
The Fermi Paradox
In the summer of 1950, the Italian American physicist Enrico Fermi asked to some of his colleagues during a lunch break: “Where is everybody?”, referring to the lack of evidence of extraterrestrial civilizations. This question is popularly referred to as The Fermi Paradox.
Since the question was formulated and popularised, people from different backgrounds have tried to answer it. There are thousands of books and articles dedicated to the subject. These documents list solutions, as they are called, to the Fermi Paradox. Traditionally, a good portion of the solutions are framed within the context of the Drake Equation, a probabilistic argument introduced by Frank Drake in 1961. Drake’s goal was to stimulate a scientific dialogue around the existence of technological civilizations.
The Drake Equation
The Drake Equation aims to provide an estimation of the number of technological advanced civilizations in the Milky Way. Some of the terms in the Drake Equation discuss about the possibility of the universe not having enough planets, or planets not being at the right distance of their home star to allow life to flourish. Other terms bring the topic of how long a civilization could survive before being able to make their presence known in the universe. Such civilizations could have gone extinct before their signals were able to reach other stars succumbing to some sort of universal great filter.
The Drake equation has been criticized and loved by many during the years, and new versions have been proposed. One of the most popular versions is undoubtedly The Seager Equation [3], presented by MIT Prof and astrobiologist Sara Seager. Prof Sara proposes a probabilistic argument that is based on our current tools and limitations and permits to calculate the odds of finding life based on the detection of biosignatures.
The Great Filter
The Great Filter is the idea that civilizations exhibiting human-like intelligence are required to go through multiple hurdles before they can colonize the universe. Some civilizations, though, might just be silent on purpose, afraid of any unknown danger out there.
An asteroid similar to the one is believed to have killed the dinosaurs, a dangerous close-by supernova, a massive solar flare, a migrating black hole, nuclear war, climate change, among others, are events that could exterminate all intelligent life on a planet. If a civilization is able to overcome all these filters, then perhaps such civilization can continue their technological progress and reach for the stars.
What about us? Have we already overcome the filters that we needed to overcome? Is the great filter behind or ahead? Finding another civilization could teach us so much about the future that is waiting for us.
In the meantime, we keep looking…
References
[1] Wright, J.T., Kanodia, S. and Lubar, E., 2018. How much SETI has been done? Finding needles in the n-dimensional cosmic haystack. The Astronomical Journal, 156(6), p.260.
[2] Lineweaver, C.H., 2001. An estimate of the age distribution of terrestrial planets in the universe: quantifying metallicity as a selection effect. Icarus, 151(2), pp.307–313.
[3] Seager, S., 2018. The search for habitable planets with biosignature gases framed by a ‘Biosignature Drake Equation’. International Journal of Astrobiology, 17(4), pp.294–302.
