Why finding evidence of extra-terrestrial life might not be such good news.

The recent announcement that the Perseverance rover found what appears to be organic molecules in rock core samples taken from an ancient lakebed on Mars was greeted by much excitement. Organic molecules form the building blocks of life, and this is the second time such molecules have been found on Mars after a previous discovery in 2014. Although indicative, these finds are not definitive evidence that life existed outside Earth and would need to be tested in a laboratory to be sure. Finding evidence that life existed on another planet in our solar system would be an amazing scientific discovery but the existential implications of such a find for the future of humanity might not be so good.

To understand why, we have to go back to the National Laboratory at Los Alamos, Texas in 1950. On a warm Summers day, four physicists strolled across campus towards the lunch hall discussing a recent spate of UFO sightings and the possibility of faster than light travel. After they reached the cafeteria and sat down for lunch, the conversation turned to other topics until suddenly and unrelated to the conversation then at hand, one of the men, Enrico Fermi asked “Where is everybody?”. He then scribbled down some rapid calculations, estimating that given the age and size of the universe we should have plenty of evidence of extraterrestrial life already since Earth should already have been visited many times.

This then formed the setting for the formulation of what has come to be called the Fermi paradox, that is, the contradiction between the apparent high likelihood that extraterrestrial civilisations exist and the fact that we see no signs of them. The universe is nearly 14 billion years old and is big on a scale the human mind struggles to understand. It’s thought that our galaxy, the Milky Way, contains at least 100 billion planets and there are thought to be around 2 trillion other galaxies in the observable universe. Therefore, although modern humans evolved on Earth about 200,000 years ago, there are potentially billions of billions of other places that civilisations could have developed and plenty of time for them to do so. Yet we detect no evidence of them.

If such civilisations did exist, then some have estimated that it would take not so long on the cosmic timescale for them to become visible. The Kardashev scale is a means of classifying civilisations according to their energy consumed or power produced. The scale as originally proposed has three levels, KI – a civilisation capable of harnessing the energy resources of a planet, KII – a civilisation capable of harnessing the entire energy of a star and KIII – a civilisation capable of harnessing the energy of a galaxy. A KII or KIII civilisation would presumably have the technology and resources to colonise an entire galaxy within the timespan of a few million years, some of the effects of which might be expected to be detectable from Earth.

One method of estimating the potential number of communicating civilisations in the galaxy is to use an equation proposed by the astrophysicist Drake, where N is the total number of communicating civilisations in a galaxy.

N = R * fp * ne * fl * fi * fc * L

In the above equation, R is the yearly rate at which stars form in the galaxy, fp is the fraction of stars that possess planets, ne is the number of planets with environments suitable for life, fl is the fraction of these planets on which life develops, fi is the fraction of those planets on which life develops intelligence, fc is the fraction of planets with intelligent life that develop a culture capable of interstellar communication or detection, and L is the average length of time for which such cultures emit detectable signals. The difficulty with producing an accurate N, is that apart from the first three parameters in the equation, estimates for the other terms can differ massively.

One could say though that if the solution to the Fermi paradox is that there are no other civilisations in our galaxy, then the values for one or more of the last four terms must be tiny i.e. life is extremely rare, intelligent life is extremely rare, civilisations capable of insterstellar travel are extremely rare or impossible, or such civilisations do not survive very long. And this brings us back to the title of the article, if evidence that life exists (or once existed) was found on another planet in our solar system it would mean that we could have more confidence that life is not extremely rare. Hence there would be only three terms left for which one or more of the values must be miniscule and if it is the case that civilisations capable of interstellar communication either never arise or do not last long, then why would we expect the future of our own civilisation to be any different? This is why finding life on another planet might not be such great news.

In a paper from the Future of Humanity Institute in Oxford it was suggested that the Fermi paradox dissolves if instead of using point estimates for the terms in the Drake equation, one incorporates estimates of the uncertainty around what the values for these terms should be into the equation. The authors used a measure called log uncertainty to estimate how many orders of magnitude our current uncertainty about the value of the different terms in the Drake equation is. They estimated the log uncertainty value for the fl term as ≥ 200 and after doing the same for the other variables and tracking this uncertainty through the equation they found a probability ranging from 53%-99.6% that we are alone in this galaxy. They suggest that the most likely reason for this is that life is rarer than we think rather than future existential threats to humanity being likely. However, finding life on another planet would surely reduce the log uncertainty of the fl term substantially. I haven’t attempted to recalculate the probabilities based on this, as yet hypothetical, scenario, but it would be interesting to see its effect. An earlier paper from researchers in Princeton who carried out a Bayesian analysis had already concluded that our current state of knowledge about abiogenesis is not inconsistent with the hypothesis that life is extremely rare. These researchers noted that finding a single case of life arising independently from humanities lineage would significantly alter their conclusions.

Less this all sounds too pessimistic, it is still the case that we haven’t found definitive evidence of life arising independently of Earth so far. There are also many other possible explanations for the Fermi paradox, if indeed it may be considered so. In fact, more than 100 different explanations have been suggested many of them quite fascinating. Stephen Webb outlines 75 of them, grouping them into three categories. The first and, in my opinion, least likely group are those that assume extraterrestrials are (or were) on Earth, the second group of explanations assumes extraterrestrial civilisations exist but we have yet to see or hear them and the third group assumes that they don’t exist. Within each of these groups the individual hypotheses are quite diverse, ranging from the absurd to the spectacular. Until scientists can narrow the range of uncertainty around the estimates in the Drake equation, these hypotheses will remain just that.

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