By Jemma Powell | Science Editor
Eight planets circle a single star in our solar system, our galaxy hosts over 100 billion stars, and there are roughly a trillion galaxies in the observable universe. Meanwhile, the mentality that humans are alone in the universe has been criticised for being narrow-minded, reasonably unlikely, and excessively dramatic. But is it true?
What are the barriers to life developing out in space?
As Stephen Webb summarised in his 2018 TED Talk, there are several fundamental barriers to life on other planets.
Simply: these so-called ‘barriers’ must be overcome for life to exist. Webb explains that we must cross a minimum of four barriers for the feasible existence of technologically advanced, planet visiting life-forms popularised by science-fiction
The first barrier considers other planets’ habitability. Webb asserts that a planet must be “just right” for life to exist – not too hot, not too cold (i.e., liquid water exists). Scientists widely recognise these as a ‘Goldilocks Planets’.
Webb’s Second Barrier refers to “the creation of life from non-life” (‘Abiogenesis’). Whilst the essential building blocks of life (amino acids, water, complex organic molecules, etc.) are found across space, from comets to interstellar dust clouds, nothing has brought these elements together to form life as we know it. Scientists still remain uncertain how this even occurred on Earth
Providing that these two barriers are crossed, it would be entirely possible (though incredibly unlikely) for some extremely simple life-forms to exist out in the universe. In order for us to find anything remotely resembling science-fiction aliens. However, to find anything remotely resembling science-fiction aliens, Webb asserts that two additional (and admittedly large) barriers must also be surpassed
The first is that organisms must have made complex technological advancements. Amongst Earth’s millions of life forms, for reference, humans are the only organisms to have developed the capacity to travel outside of the atmosphere.
Webb’s final barrier is that, even if life has developed technology sophisticated enough to leave its planet, it must also build the capacity to communicate across the universe.
Within all these barriers are thousands of micro-barriers, a single one could make it impossible to overcome the next. The Moon, for example, allows the Earth to have the stable axial tilt and the slow rotational rate empirical for the stability of our climate. But if the Moon was just a few miles bigger, the Earth’s axis would be chaotic, leading to rapid and frequent extreme climate changes which would render complex life impossible.
“Evolution”, as Webb summaries, critically “doesn’t have space travel as an end goal”.
How likely is it that intelligent life other than humans exists out on other planets?
So, with all of this considered – what is the likelihood of all these factors falling perfectly into place, and intelligent life existing in the universe?
Webb argues that there is a one in a thousandth chance of crossing each barrier (arbitrary figure). If a galaxy contained a trillion planets, how many are habitable (barrier one)? A trillion becomes a billion. How many of these planets have a stable climate? A billion becomes a million. On how many of these planets does life start? One million becomes 1000. On how many of these could complex life arise? 1000 planets become one. One planet in 1000 galaxies could develop any form of complex life. What is the likelihood of that planet developing basic science and maths? One in a million galaxies. How many could develop the necessary technologies for space travel? One in a billion. How many avoid disaster, both self-inflicted and uncontrolled? One in a trillion.
Mathematically speaking – we know that it is possible for one planet in a trillion galaxies to develop life complex enough for space travel. With only a trillion galaxies in our own visible universe, humans are the only example of this that we currently know of.
So maybe we are alone. Maybe Elon Musk’s car will forever be blaring David Bowie’s Life on Mars to an infinitely empty audience. Maybe the pessimists are right.
However, this isn’t necessarily a depressing notion. If we can appreciate that we’re probably not going to be invaded by Decepticons, blown up by Vogons, or enslaved by Sentinels, and equally appreciate that we’re never going to be saved by a Time Lord in a TARDIS, maybe then we can start to understand that we are the only ones, out of trillions, who got lucky enough to exist. Maybe all those amazing, ethereal, God-like beings we dreamed aliens could be in the past… maybe they could be our future.Jemma Powell Science and Technology