News stories about the likely existence of extraterrestrial life, and our chances of discovering it, are generally positive. We are often told that we can discover it at any moment. Finding life beyond Earth is “just a matter of time,” we were told in September 2023. “We are close” was the September 2024 headline.
It’s easy to see why. Headlines like “We’re probably not close” or “No one knows” aren’t very clickable. But what does the relevant community of experts actually think, taken as a whole? Are optimistic forecasts common or rare? Is there even consensus? In our new paper, published in Nature Astronomy, we found out.
From February to June 2024, we conducted four investigations into the likely existence of basic, complex and intelligent extraterrestrial life. We sent emails to astrobiologists (scientists who study extraterrestrial life), as well as to scientists in other fields, including biologists and physicists.
A total of 521 astrobiologists responded and we received 534 responses from non-astrobiologists. The results show that 86.6% of astrobiologists surveyed responded with “agree” or “strongly agree” that it is likely that extraterrestrial life (of at least a basic kind) exists somewhere in the universe.
Less than 2% disagreed, while 12% remained neutral. Based on this, we could say that there is a solid consensus that alien life, in some form, exists somewhere out there.
Scientists who were not astrobiologists essentially agreed, with an overall agreement score of 88.4%. In other words, you cannot say that astrobiologists have a preference for believing in extraterrestrial life compared to other scientists.
When looking at “complex” alien life or “intelligent” aliens, our results were 67.4% and 58.2% agreement for astrobiologists and other scientists, respectively. So scientists are inclined to think that alien life exists, even in more advanced forms.
These results are made even more important by the fact that disagreement was low for all categories. For example, only 10.2% of astrobiologists disagreed with the claim that intelligent aliens probably exist.
Optimists and pessimists
Are scientists just speculating? Normally, we should only take note of a scientific consensus if it is based on evidence (and lots of it).
Because there is no good evidence, scientists are left to guess. However, scientists did have the option to vote ‘neutral’, an option chosen by some scientists who thought they would be speculating.
Only 12% chose this option. There is actually a lot of ‘indirect’ or ‘theoretical’ evidence that alien life exists. For example, we now know that habitable environments are very common in the universe.
We have several in our own solar system, including the subsurface oceans of the moons Europa and Enceladus, and perhaps the environment a few kilometers below the surface of Mars. It also seems relevant that Mars used to be very habitable, with lakes and rivers of liquid water on its surface and a significant atmosphere.
It is reasonable to generalize from here to a truly gigantic number of habitable environments in the Milky Way and the wider universe. We also know (since we’ve been here) that life can arise from non-life – it happened on Earth, after all.
Although the origins of the first, simple life forms are poorly understood, there is no compelling reason to think that this requires astronomically rare conditions. And even if it is, the chance of life arising (abiogenesis) is clearly not zero.
This can help us see the 86.6% agreement in a new light. Maybe it’s not actually a surprisingly strong consensus. Perhaps it is a surprisingly weak consensus. Look at the numbers: there are more than 100 billion galaxies. And we know that habitable environments are everywhere.
Let’s say there are 100 billion billion habitable worlds (planets or moons) in the universe. Suppose we are such pessimists that we think that the chances of life getting started on any given habitable world are one in a billion billion.
In that case, we would still answer “agree” to the statement that it is likely that extraterrestrial life exists in the universe.
So optimists and pessimists should all have answered ‘agree’ or ‘strongly agree’ to our survey, while only the most radical pessimists about the origin of life disagreed.
With this in mind, we could present our data in a different way. Suppose we ignore the 60 neutral votes we received. Perhaps these scientists felt they would be speculating and did not want to take a position.
In that case, it makes sense to ignore their voices. A total of 461 votes remain, of which 451 agree or strongly agree. Now we have an overall agreement rate of 97.8%.
This move is not as illegal as it seems. Scientists know that if they choose “neutral,” they cannot possibly be wrong. So this is the “safe” choice. In research this is often called ‘satisficing’.
As the geophysicist Edward Bullard wrote in 1975 while debating whether all continents were once connected, rather than making a choice it is “wiser to remain silent, … to sit on the fence and wait in statesmanlike ambiguity for more data’. Not only is silence a safe choice for scientists, it means the scientist doesn’t have to think too hard – it’s the easy choice.
Finding the right balance
What we probably want is balance. On the one hand we have the lack of direct empirical evidence and the unwillingness of responsible scientists to speculate. On the other hand, we have evidence of a different nature, including the truly gigantic number of habitable environments in the universe.
We know that the probability of life beginning is not zero. Perhaps an 86.6% agreement, with 12% neutral and less than 2% disagree, is a sensible compromise all things considered.
Perhaps, given the problem of satisficing, when presenting such results we should present two results for overall agreement: one that includes neutral voices (86.6%), and one that excludes neutral voices (97.8% ). Neither result is the only correct result.
Each perspective addresses different analytical needs and helps avoid oversimplification of the data. Ultimately, reporting both numbers – and being transparent about their context – is the most honest way to reflect the true complexity of the responses.
Peter Vickers, Professor of Philosophy of Science, University of Durham; Henry Taylor, Associate Professor, Department of Philosophy, University of Birmingham and Sean McMahon Reader in Astrobiology, University of Edinburgh
This article is republished from The conversation under a Creative Commons license. Read the original article.
