Are We Alone?

10% of the Milky Way planets are positioned in the habitable zone, meaning there are upwards of 100 billion planets where there is the potential for life to appear. Taking Earth as an example, life appeared as soon as the conditions were agreeable. This can only convince physical scientists that life is not uncommon in the Universe. However, what if they are mistaken. This article will argue the possible explanations for the Great Silence.

?Drake Equation

Through the Principle of Mediocrity, we might conclude that intelligent life should exist on many other planets. This begs the question, why have we not uncovered this so-called abundance of life? Using the optimistic N = L notion of the Drake Equation, we can start to see the probable complications with detecting alien life. Say L = 3000, and we assume these 3000 technical civilisations are evenly spread throughout the Milky Way, then the average distance between them would be approximately 1000 light years. Because radio waves, and all electromagnetic waves, become weaker with the square of a distance, a signal transmitted from this distance reaches Earth one million times fainter than one emitted 1 light year away (Maccone, 2012). Civilisations would run in to difficulty of even detecting this leakage radiation from each other. If there are only a few technical civilisations, the space between them will be larger and contact could become undetectable.

Extra-terrstrial communication (or lack thereof)

It is a real worry from SETI researchers that extra-terrestrial communication could pass us by merely because we do not understand it to be communication; and vice versa. Even the mathematical ‘universal’ Lincos language (Freudenthal, 1960), fashioned from the study of Xenolinguistics, contains large errors in the form of potential confusion. It is argued that it still incorporates human culture and experiences, on the basis that our mathematics may not universal, and therefore is inconceivable to an alien ear or eye. This is so far the best method of communication we have, but we cannot be certain this is a workable universal language. It is reasonable to assume that extra-terrestrial civilisations may also use unknown technologies to us. They could have adopted technology far more advanced than radio waves, assuming with L = 3000 that any extra-terrestrial civilisation that we do come in to contact with will most probably be older, and more advanced than us. It is highly likely that any transmissions we do receive, will be faint, transient (if located on a rotating stage like a planet) and with characteristics that are completely unknown to us. They could easily go undetected.

?The Weird Life hypothesis

Could it even be our Earth-centric definition of life is preventing us from detecting technical civilisations? The ‘Weird Life’ hypothesis (Davies, 2007) suggests we may not be able to detect whether a structure is alive simply by looking at its components. The factors we think are essential to life may just be peculiar to life on Earth. After all, every lifeform on Earth is known to be derived from our single common ancestor, LUCA. Our closest technical alien civilisation may not be formed out of DNA, may be silicon-based instead of water-based, and may not even be a solid. In the words of Josh Gabbatiss (2017) ‘What a tragedy it would be if in the 2020s the new Mars rover trundles straight past a Martian, simply because it does not recognise it as being alive.’

?Human messages into space

The most a METI message has ever travelled is 0.1% of the Milky Way (Kirby, 2019). For this reason, scientists do not expect their messages to be received. The problem then becomes, the universe could be teeming with intelligent civilisations, but they are dispersed widely through space and time, never crossing paths with us. Unless we can send messages faster than the speed of light, this will be a great setback METI and SETI face forever. The expanding universe makes prospects even more dismal. It is logical then to assume we could never arrive at the statement that we are alone, but rather give up on finding intelligent lifeforms elsewhere. SETI will most probably always be limited to searching nearby stars.

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The chances of intercepting a beamed signal are next-to-none unless one is fortunate enough for the transmitting telescope and the receiving telescope to be pointing right at each other. We simply don’t know where to point our telescopes and our current field-of-view, or lack thereof, slows down the search a great deal. The Milky Way is home to 300 billion stars, and if N ~ 3000, a survey of 100 million stars would need to be done before we can realistically expect to find a populated solar system. Furthermore, we can only vaguely guess which dominant frequency will be used to transmit an alien signal - the range of the radio spectrum is enormous, spanning nine orders of magnitude from KiloHertz to TeraHertz (O’Brien et al. 2019). The wide range of Doppler drifts to apply will only make the search more difficult.

?Limits of technology

It could be as simple as a technological breakthrough revealing life beyond Earth. The ability to look for techno-signatures in very distant galaxies, such as unexpectedly bright infrared emissions, gives a tiny sliver of hope to our search. We can only assume civilisations on the Kardashev Type 1-3 (Creighton, 2014) will have great energy requirements, and with this, plenty of waste heat. Even our current generation of telescopes should be able to pick up on this excess emission in the mid and far Infrared. This begs the question, why have we not detected any? Dr Forgan et al. 2019 affirmed “if you imagine the Milky Way as a football field, we have searched an area no bigger than the penalty spot." It is important to remember that SETI is still in its infant stage. Those that see the lack of evidence as being an indicator of no intelligent extra-terrestrial life, may be misguided. We have many technological and space faring barriers to overcome in order to find intelligent life elsewhere. It may not be the Great Silence, but rather the Great Wait.

?Biology of life

The Late Heavy Bombardment made the early Earth a place not encouraging to life. For this reason, the unstable young parts of the Universe are much less likely to contain life. Our large moon has stabilised Earth’s spin, and the strong magnetic field generated in the Earth’s molten iron core acts as armour against harmful particle radiation from the sun (O’Brien, 2019). Life has flourished on Earth, and it is thought that the giant planets were vital to this. Their gravitational power swept the solar system clear of the remaining debris left over from the formation of the planets. The principle of mediocrity does not go as far as the order within solar systems, with many gas giants forming the inner system instead. This means that the Earth could be rare or unique in its ability to provide the requirements of life; formally known as the ‘Rare Earth’ hypothesis (Bounama et al. 2007). Geology has unequivocally formed the history of life on Earth. Evolution has been moulded by mass extinction; the last, the Late Cretaceous, eliminating the dinosaurs and paving the way for the life of mammals. Without this chance event, humans may never have become the dominant species on Earth.

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Biologists caution that there is nothing inevitable about the creation of simple life, let alone intelligent technical civilisations, where ours emerged after a great 4 billion years of evolution. Intelligent life on Earth has risen from a long series of chance events, owed a great deal to how natural selection has responded to random climatic events, which may never be repeated in the Universe ever again. Most life is still single-celled, and most animals are not complex. Evolution really does not have any direction; as a result, the outcome is neither foreseeable nor determinable (Smith et al. 1997). Eukaryogenesis was the key step for intelligent life to be made possible on Earth but has only be known to happen once in 4 billion years, suggesting that multi-cellular life in the Universe is rare and possibly next-to-none (Davies, 2010). The binding of a bacteria and archaea is in all practical terms, impossible, so there is no tendency for this to happen again, ever. Without this, life would have never occurred beyond the microscopic. Corvids are far more intelligent than the average mammal, so why have they not developed intelligence like ours? The answer is simple; human abilities arose from our social organisation; the need to understand the desires of other members and thrive in cruel environments. A change in climate could have led to a very different evolutionary response by our ancestors. This leads us to the finale of Fermi’s paradox, there are no alien civilisations.

?Time Space Complex

If the typical lifetime of a civilisation is short, this might be one of the ‘great filters’ that could help explain why we have not seen any evidence for other technical civilisations in our own Galaxy (Hansen, 1998). When we think about our own challenges we have to overcome to survive as a species; nuclear war, global warming, resource depletion, overpopulation, supernova explosions, unavoidable comet collisions, ice ages, how long do we really think we have left before our civilisation is wiped out? Take supernovas, for example. There are 100 stars currently within the Earth’s lethal radius. The energy of a supernova would be 10x greater than needed to completely annihilate the Earth. It is predicted that within this radius, a star will die every 100 million years (Garrett, 2019). This reality would also be similar to other alien civilisations and threaten their chances of survival. According to Steffen et al. 2011, “climate change is only the tip of the iceberg” for our ‘great filter’ lying ahead of us. A study by the UN (2017) on the maximum carrying capacity of the Earth places a limit of 8 billion people – which we should reach by 2030. Technical civilisations may be inherently unsustainable even on relatively short timescales of a few hundred years, and therefore always subject to immediate collapse almost as soon as they appear. Maybe there are no civilisations that reach Type I, this is the ‘extinction’ hypothesis.

?Alien sightings

A more questionable alternative is that we have already come into contact with intelligent extra-terrestrial life, and there has never been a Great Silence. The baffling resemblance of pagan myths to abduction accounts are frequently used as testimony that aliens have been conducting visits for hundreds of years. For example, in 1645 a Cornish teenager named Anne Jeffries alleged to have been assaulted by “little men” whilst she was unconscious. She had been paralysed as they took her up to their “castle in the air” where they molested her and then sent her home but continued to assault her regularly (Enns, 1999). Accusations of this kind are not nearly unheard of. John Mack, a Harvard Professor who has become infamous for his belief in abduction stories, has theorized that aliens exist in an alternate dimension which we cannot observe; they live in our dreams. Indeed, the number of abductees has risen so dramatically that, according to the last Roper poll, two percent of Americans are being abducted regularly (Blackmore et al. 2000). Yet, only more recently has a consensus emerged of what these aliens look like. The earlier lack of consensus is a strong argument against the so-called abductions. Carl Sagan described this phenomenon in 1993 as an “epidemic of hallucinations”. There is no doubt that these reported abductions are captivating though, and to abductees minds, wholly real.

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It is plausible that we are alone, but the most compelling argument for the Great Silence is the space-time continuum. Our SETI and METI technologies cannot infiltrate into deep space in a timely fashion that would give us results by now, or for many years to come. Humans concept of time is extremely short, and it is not unreasonable that we have yet to find evidence after only 60 years of searching. The find of a simple alien lifeform would bring this debate wide open, as this suggests Abiogenesis is universal, making it more credible that Eukaryogenesis could be universal too, opening up the potential path for extra-terrestrial intelligent life to flourish. For the sake of humanity and in the famous words of Otto Struve, ‘To the value of L. May it prove to be a very large number!’ (Billings, 2014).

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