Situated in the Bay of Bengal, forming part of an archipelago known as the Andaman Islands, lies the small but striking North Sentinel Island. This island, officially part of India, is home to one of Earth’s last uncontacted people: the North Sentinelese. Living alone, isolated and untouched by modern civilisation, these people, aside from the occasional- usually hostile- encounter, will have virtually no knowledge of the wider world. Despite on an official level being citizens of India, it is unlikely they will even know what India is. The North Sentinelese, having been isolated on their home island for thousands of years, have lived beyond the realm of the world wide community. Yet, despite their lack of technology, education or access to the media- and the fact they never leave their island (except for fishing in the immediate waters)- it is very likely they know that they are not alone in the world. Although they likely aren’t aware of modern society, technology and politics- they will have seen clues alluding to the fact they are not alone. They will have spotted planes, boats and helicopters and have had the occasional visitor from the outside world. Despite their isolation, they will know there is fellow beings out there, perhaps more numerous and more advanced. They have made no attempt to contact the outside world, but they know we are here- as we are impossible to miss. If this idea is projected onto a galactic level, why have we yet to see clues of advanced alien races across the void of space? They have had millions- perhaps billions- of years to develop, industrialise and leave their mark on space, yet we have never found solid evidence to confirm this.
Humanity has many questions about the universe, and many things even the most advanced physicists and scientific minds cannot explain. The one thing we can say with absolute certainty is that the universe is clearly engineered in such a way that advanced, intelligent life can arise within it. We know this because, well, we are here. However, we are the only known example of an advanced civilisation in the universe. In a vast universe which is clearly suitable for advanced life to exist, common sense would dictate that advanced civilisations should be fairly common- and easily detectable from Earth. But, unless you believe various conspiracy theories, we are yet to detect another civilisation either in our galaxy or beyond.
The Fermi Paradox, named so after its proponent the Italian-American physicist Enrico Fermi (1901-1954) seeks to answer where extraterrestrial civilisations are, given that our civilisation is extremely young in cosmic terms, there has been ample opportunity for countless other civilisations to arise and develop interstellar travel and intergalactic influence. However, we have yet to witness clear evidence of such exocivilisations either in our galaxy or beyond. In theory, the activities of a highly advanced species should be fairly easy to spot in the vastness of space. Especially those of a Kardashev Type II civilisation who harness the entire energy of a star, or especially a Type III civilisation who do the same but with an entire galaxy. Physicist and Mathematician Freeman Dyson (1923-2020) proposed such advanced beings would require immense amounts of energy and may build structures known as Dyson Spheres around stars to encase them and harness all the energy emitted. These should be reasonably easy for astronomers to come across, as an unusually dim star could be an indication of such a construction, as would a star emitting only infrared radiation, as this would be a by-product of the Dyson Sphere radiating out as it captures the energy of the star. In fact, in 2015 astronomers working on behalf of the Planet Hunters Project noted the unusual dimming of a star known as KIC 8462852 (commonly known as Tabby’s Star) which could not be attributed to normal stellar behaviour. Many hypothesis were put forward, including the possibility of a Dyson Sphere, a Dyson Swarm or some other kind of artificial megastructure in orbit around the star, which is an F-type main sequence star located in the Cygnus constellation. Eventually, it was decided that the dimming was the result of a large and irregular field of space dust blocking some light from the star. Unusual, but not the smoking gun for an extraterrestrial race we were hoping for!
The Drake Equation
The founding father of modern SETI (Search for Extra Terrestrial Intelligence) Frank Drake aimed to determine, mathematically a rough estimate as to how many intelligence civilisations existed in the Milky Way galaxy. In 1961, he wrote what is now known as the Drake Equation:
N=(R*)(fP)(ne)(fL)(fi)(fc)(L)
According to SETI, these values consisted of:
N = The number of civilizations in the Milky Way Galaxy whose electromagnetic emissions are detectable.
R* = The rate of formation of stars suitable for the development of intelligent life.
fp = The fraction of those stars with planetary systems.
ne = The number of planets, per solar system, with an environment suitable for life.
fl = The fraction of suitable planets on which life actually appears.
fi = The fraction of life bearing planets on which intelligent life emerges.
fc = The fraction of civilizations that develop a technology that releases detectable signs of their existence into space.
L = The length of time such civilizations release detectable signals into space.
Using our own solar system as an example for base values, Drake concluded our galaxy likely includes at least 1,000 technological civilisations. With more generous figures in the equation, this could even be advanced to 100,000 or more. With the number of cosmic neighbours out there potentially this high, this once again brings up the Fermi Paradox. If technological civilisations are abundant in our own galaxy, why have we yet to detect any signs of them? It is estimated that any hypothetical technological civilisation utilising radio technology within around 100 light years of Earth would be able to detect our own civilisation with relative ease. Assuming many of these civilisations may have been around for thousands, millions or hundreds of millions of years before Earth, there should be ample time for radio wave communications from exocivilisations to reach us on Earth, whether they are intentional attempts at contact or simply leakage from their home planet. However, we have yet to detect any credible radio signals that are undoubtedly from technologically advanced exocivilisations. This is known in radio astronomy as The Great Silence. In a galaxy, vast but teeming with intelligent beings, if the Drake Equation is indeed correct, we should be able to pick up signs of these civilisations relatively easily. So why haven’t we?
Luke’s Astronomy and Astrobiology blog 