The concept of extraterrestrial life is one that never fails to inspire and amaze – influencing countless movies, books, and stories. We live in an age in which technological advancements have enabled us to seek signs of life elsewhere in the cosmos. The Fermi Paradox seeks to answer the apparent deficiency of extraterrestrial life. This article explores the Fermi Paradox and what the discovery of aliens or lack thereof suggests for humanity, as well as current developments in the field of space technology.
1. An overview of our galaxy and beyond
The milky way is vast, spanning over 100,000 light-years in diameter  and 13.5 billion years old ± 800 million years. It is said to be one of the first galaxies that formed within our universe, which is 13.7 billion years old ± 200 million years . There are over 200 billion other galaxies with billions of star systems within them, suggesting that we could just be another civilisation within a vast and living universe. Named after the Italian physicist Enrico Fermi, the Fermi Paradox is the contradiction between the high probability estimations of the presence of extraterrestrial life and its apparent absence. It seeks to answer the question “Are we alone in the universe?” and remains one of the most debated mysteries of science.
2.The Fermi Paradox
There are billions of stars within our galaxy and there is a significant probability that some of these are orbited by Earth-like planets. A recent study by the Proceedings of the National Academy of Sciences of the United States of America (PNAS) found 22% of Earth-like planets are orbiting sun-like stars in their habitable zones, with the nearest probably only 12 light years away . Assuming even a small proportion of these planets developed intelligent life and that interstellar travel is possible, it would take only a few million years to colonize the galaxy  – a relatively short time on both geological and astronomical scales. On this basis we should long have come in contact with another life form, yet we have not. This lead Fermi to ask one important question – why?
Scientists have proposed a few answers to this question. Arguably, the most famous is the existence of what is known as ‘The Great Filter’. In the context of The Fermi Paradox, The Great Filter  is a hypothetical barrier which is extremely difficult for life to surpass. If we were to discover aliens commonly and life was abundant through the galaxy, it would mean The Great Filter is likely ahead of us. Therefore, we would be set to encounter it somewhere in the future, suggesting a bleak future for humanity, as it would be difficult for life to surpass this. However, if, perhaps, we are truly alone and fail to discover life, then we can hypothesise that we have passed The Great Filter. It is not known in what form the Great Filter has manifested or will manifest itself as.
Some believe The Great Filter was abiogenesis. Abiogenesis is the evolution of life from inorganic substances. This gradual evolution of life from single-celled organisms to complex, multicellular organisms occurred on our planet more than 3.5 billion years ago and was eventually preceded by biogenesis – the theory that life arises from life. Others believe we carry the seeds for our own destruction, and that it may be climate change or a nuclear war. Whatever the truth, humanity understands that no sign of alien life is a good sign, indicating The Great Filter is behind us.
Despite its popularity, The Great Filter is not the only plausible explanation to The Fermi Paradox.
One similarly popular explanation is the simulation argument, which includes the idea that an alien species has created a simulation so that the universe appears lifeless.  Proposed in a paper written by Nick Bostrom, a philosopher at the University of Oxford, the simulation argument states that if a species at our current level of development can avoid extinction, and they are interested in running computer simulations of minds like our own, then we are almost certainly living in a simulation. Bostrom implies that if we are living in a simulation, we should not change our way of living. Instead we should try to predict what would happen next in our simulation through the extrapolation of past trends and scientific modelling.
Another explanation to The Fermi Paradox is the Rare-Earth hypothesis. The Rare-Earth hypothesis argues that the conditions which lead to the survival of life on Earth are too rare. The Earth has conditions which support life: it is in the Sun’s habitable zone, has a required magnetic field, the correct atmospheric composition, and the presence of oceans and plate tectonics. The Rare-Earth hypothesis suggests this combination of conditions does not occur frequently enough on other planets simultaneously as they do on Earth for life to be discovered.
Another notable explanation is that we have already been visited. Perhaps aliens paid Earth a visit several thousand years ago when we were unable to detect them. Or perhaps, more chillingly, they are here now and remain undetected.
Some believe intelligent life is absent elsewhere in the universe and that it resides in a primitive state. If abiogenesis truly is the Great Filter, extra-terrestrial species may remain in a primitive state and therefore lack the technology required for space travel. Others believe civilisations are too far apart. As the universe is continually expanding it remains a possibility that contact may never be established if intelligent life was present in another galaxy.
3.Developments in space technology: LIGO and LISA
Life is not the only thing we search for in the universe. The ability to explore and observe resides not only in the cosmos with the National Aeronautics and Space Administration’s (NASA) rovers but right here on Earth. The Laser Interferometer Gravitational-Wave Observatory (LIGO) was the first to detect gravitational waves from the collision of a binary pair of neutron stars 130 million light-years away. This event caught the attention of thousands of astronomers and was observed by telescopes on every continent. LIGO’s discovery was pivotal for astronomers. It confirmed the speed at which the universe is expanding, proved that neutron star mergers emitted bursts of gamma rays and enabled us to observe nucleosynthesis. Gold over ten times the Earth’s mass was formed along with other heavy elements like lead and platinum.
The success of LIGO inspired the creation of another, much bigger observatory. The Laser Interferometer Space Antenna (LISA) is a project set to launch in 2030 as a collaboration between NASA and the European Space Agency (ESA). It will span millions of miles and consist of three spacecraft observing changes of less than the diameter of a helium nucleus – 1.86 Angstroms – over a distance of a million miles.
4.The Kardashev Scale
Despite the advancements mentioned above, humanity still has a long way to go. The Kardashev scale, proposed by Russian astrophysicist Nikolai Kardashev, classifies civilisations into three types based on their energy consumption. It is based on two assumptions.
1. The scale and activity of any civilisation are restricted only by scientific and natural factors. 2. Civilisations have no limitations on the scale of their activities.
A type I civilisation is one that can harness the energy of all the resources on their planet. Humans are not yet a type I civilisation, but rather a type 0.7 one. This value was ascertained in 1973 when astrophysicist Carl Sagan proposed defining values for the energy consumption of each civilisation. This was done by interpolating and extrapolating Kardashev’s values using the following equation:
where is equal to the Kardashev rating and is its energy consumption in watts. We are set to reach type I status in the next few hundred years as stated by physicist Michio Kaku. The energy consumption of a type I civilisation would be in the range of to watts. Earth’s current consumption is around watts.
A type II civilisation can harness the entire energy of their parent star. One particular proposal of this is the Dyson sphere, a hypothetical megastructure consisting of orbiting solar cells that would encompass the Sun to harness its entire energy. The energy consumption of this civilisation would be around watts.
A type III civilisation is one that can harness the energy of its host galaxy. Theoretically, this could be done by harnessing the energy released from supermassive black holes, or capturing the energy of gamma-ray bursts. The energy consumption of this civilisation would be around watts.
The mediocrity principle states that the conditions that led to life on Earth are not in any way special, and therefore could have occurred throughout the cosmos. Assuming this, the Earth – at 4.54 billion years old – can be compared to a hypothetical 6 billion-year-old planet Y. Further, supposing technological advancements occurred at a similar pace, planet Y would be 1.46 billion years ahead of us. Considering modern humans arose a mere 200,000 years ago and civilisations 6,000 years ago, the progress that 1.46 billion years of advancement could lead to would be profound.
Humanity has always been mesmerised by what lies beyond our planet and the possibility of another life form looking back at us with the same wonder and fascination. Given the age and magnitude of the universe, it is hard to believe we must be its sole inhabitants. It is only in the last few hundred years that technology has allowed us to explore the cosmos. What was once a topic of science fiction is now accepted by people across our planet, spurring those who look up at the night sky to keep looking.
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About the Author
Shannon Rennie is a sixth form student currently studying A-levels in Maths, Physics, Chemistry and Geography and aims to pursue career in astrophysics. Her interests include kayaking, aviation and literature.