The challenge of discovering extraterrestrial life

Since the dawn of time, humans have been entranced by the night sky and the mysteries it withholds. Every advanced culture documented a certain obsession with space and the concept of another life form existing out there – the Greeks and Romans frequently debated the notion, with one Roman Epicurean poet Lucretius saying, “Nothing in the universe is unique and alone and therefore in other regions there must be other earths inhabited by different tribes of men and breeds of beasts.” However, it was only a short while ago that SETI, an organisation dedicated to the discovery of extra-terrestrial species, was set up. There have been many concerted efforts by humanity to find other beings somewhere in the universe, but so far nothing has been found, which begs the question: is anything actually out there?

The Fermi Paradox, named after Italian scientist Enrico Fermi, is the supposed discrepancy between the lack of evidence supporting the existence of extra-terrestrial life, and the probability of another civilisation having developed somewhere. There have been many estimates of the likelihood of alien presence in the Milky Way galaxy, most notably the Drake equation, but despite all the signs pointing to yes, we still have yet to find any concrete evidence. After all, it is approximated that there are billions of stars in our galaxy, a vast number of which could have planets with Earth-like qualities. Many of these stars, and consequently their planets, are billions of years older than our sun, meaning hypothetically they could have developed intelligent life many years prior to the existence of humans on Earth. If these civilisations are as advanced as we believe them to be, assuming they established some form of interstellar transportation, in theory they should have spanned the entire Milky Way galaxy millions of years ago. Therefore, based on this understanding, extra-terrestrial life should already have visited Earth, yet there is no substantial evidence indicating this statement is true.

One possible explanation for the absence of fact-based proof is that we, as intelligent beings, had the great misfortune of “missing” extra-terrestrial contact. As famous scientist Carl Sagan once said, “We are like butterflies who flutter for a day and think it is forever.” In terms of the lifespan of the universe, the presence of humanity is similar to the blink of an eye – insignificant, and easily missed. It is undoubtedly possible that we were not around to witness a time when interstellar travel was flourishing amongst other developments and are therefore not aware of the vast numbers of other civilisations there are out there.

Another reason we may not have found anything is that it is undeniably hard to detect living organisms on distant planets. Levels of gases that are linked to metabolising organisms, such as oxygen and methane, are often far too low in the air to be observed from further away, therefore it is very possible that we may have assumed that some planets are barren when in fact, they are teeming with organisms. On the other hand, this could also mean that extra-terrestrials are not detecting life on Earth, as the aforementioned gases could be impossible to detect over such great distances.

Despite the continuous efforts of scientists across the globe, we are still left asking why humans have not discovered extra-terrestrial life yet. Are we missing alien visits by a few million years? Are our technologies not advanced enough yet to find them? Or perhaps alternative civilisations simply do not exist; they are merely a fairytale conjured up to assure us that we are not alone in this vast expanse of empty space. Many planets that share similarities with Earth have already been located, although it is still unclear as to whether these discoveries will eventually uncover other life forms, or if they will be disappointingly desolate. Either way, it is clear that scientists will continue to search for evidence of extra-terrestrial life, to determine the answer to the ultimate question: are we alone?

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