From the philosophers of Ancient Greece to the modern day, humanity has always wondered if we are
alone in the universe. After thousands of years the question remains: will we ever find alien life?
In 1950, Enrico Fermi asked the pivotal question: “Where is everybody?”, highlighting the apparent contradiction between the likelihood that other intelligent life exists and the fact that we have never been able to find it. This is now known as the Fermi paradox. From the Drake Equation, created by Frank Drake in 1961, we can predict the existence of at least ten intelligent civilisations that should be detectable from Earth in the Milky Way alone. In spite of this, it’s radio silence from space. Drake’s Equation depends on a host of factors relating to the probabilities of life appearing and developing into an intelligent civilisation, and the length of time that an intelligent civilisation is detectable for.
It is largely assumed that alien life would require conditions similar to the ones on Earth to develop. This idea is mainly centred around the distance a planet is from its star – it must lie in the star’s ‘habitable zone’ where the climate of the planet is such that water can exist in its liquid form on the planet’s surface. In addition to water, a planet must also have a host of elements, including carbon, nitrogen, hydrogen, phosphorus and sulphur, which form the basic ‘building blocks’ of life.
However, these aren’t necessarily the only conditions that life can develop in. It has been suggested in recent years that Europa, one of the largest moons of Jupiter, could have life under its vast oceans, despite the fact that it is outside of the solar system’s habitable zone, meaning the surface of the oceans are covered in ice. This year, the James Webb space telescope was used to find evidence of carbon under one of Europa’s oceans, building more evidence for the possibility of life. If life exists on Europa it will be far from an intelligent civilisation, but the prospect of alien life within our own solar system brings hope to the chances of finding it in the rest of the universe.
If life is able to develop, there are a number of theories as to why we have never come across it. One of the main ones is known as the Great Filter. This theory states that there is some barrier to the evolution of life, either before or after it develops enough to be detectable. This ‘filter’ has been theorised to be very near to the beginnings of life, possibly in the creation of life itself or in the jump from prokaryotic to eukaryotic cells. This would mean that the chances of there being any other life in the universe at all is very slim. Alternatively, it has been suggested that after the development of technology that makes a civilisation detectable, the civilisation also develops technology that ultimately destroys them. Comparisons can be made with Earth and recent developments such as nuclear weapons and climate change. The estimation that there could be at least ten intelligent civilisations in the Milky Way assumes that a planet will produce detectable activity for at least 100 years, but if a civilisation destroys itself in a short amount of time after starting to produce activity, this estimation reduces significantly.
The Great Filter therefore suggests that humanity is either a rare example of a species overcoming the filter, or comes with the daunting implication that we may not survive as a civilisation for much longer. However, it is only one of many theories as to why we have never come across other
intelligent life. In 1975, astrophysicist Michael Hart published “An Explanation for the Absence of Extra-terrestrials on Earth”, which suggested a multitude of reasons why aliens have never come
to Earth. For example, it could be that aliens are simply uninterested in communicating with us, or that they have not existed for long enough to have the resources to do so. Hart suggested
that aliens may have even already visited Earth at some point without making contact with us – we have only been on the lookout for alien life for a short amount of time compared to the age of the universe. Generally, we have a picture of intelligent civilisations as being similar to us in motivation and
technology, but whatever life has developed separately from us could be vastly different to us and therefore not prioritise making contact with other life in the same way we do.
As it is, there are massive uncertainties and unknowns when it comes to estimations made in the Drake Equation, so we may never know whether there actually is other life out there. Despite the apparent impossibility of finding alien life within our lifetimes, humanity will continue to search for years to come to find out if we really are alone in the universe
