Most likely, our theories about the search for alien life are wrong.
If we found evidence of alien life, would we be willing to realize it? Life on other planets may be so different from what we are used to that we may not recognize any biological signatures it produces.
In recent years, there have been changes in our theories about what counts as a biosignature and which planets might be habitable, and further changes are inevitable. But the best we can really do is to interpret the data we have with our current search theory, not some future idea that we haven't had yet.
This is a big problem for those looking for extraterrestrial life. As Scott Gaudí of NASA's Advisory Board said: “One thing I’m quite certain; now, having spent over 20 years in this area of exoplanet search … expect the unexpected."
But can you really “expect the unexpected”? Many breakthroughs happen by accident, from the discovery of penicillin to the discovery of the cosmic microwave background radiation left over from the Big Bang. They often reflect the degree of luck on the part of the researchers. When it comes to alien life, is it enough for scientists to assume that “we will know them when we see them”?
Many results tell us that it is extremely difficult to expect the unexpected. “We often miss what we don't expect to see,” says cognitive psychologist Daniel Simons, known for his work on inattentive blindness. His experiments showed how people can miss a gorilla pounding on the chest in front of their eyes. Experiments like this also show how blind we are to non-standard playing cards such as the black four of hearts. In the first case, we skip the gorilla if our attention is busy enough. In the latter case, we miss the anomaly because we have strong prior expectations.
There are also many relevant examples in the history of science. Philosophers describe this phenomenon as “observation-laden theory”. What we notice sometimes depends quite heavily on our theories, concepts, underlying beliefs, and previous expectations. Moreover, what we consider to be significant may be biased.
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For example, when scientists first found evidence of low atmospheric ozone over Antarctica, they initially dismissed it as bad data. Without a prior theoretical reason to expect a hole, scientists ruled it out beforehand. Fortunately, they were set to double check and the discovery was made.
Could something like this happen in the search for extraterrestrial life? Scientists studying planets in other solar systems (exoplanets) are amazed at the plethora of possible observational targets competing for their attention. Over the past 10 years, scientists have identified more than 3,650 planets - more than one per day. And with missions like NASA's exoplanet hunter TESS, that trend will continue.
Each new exoplanet is rich in physical and chemical complexity. It is all too easy to imagine a case where scientists do not double-check a goal that is labeled “irrelevant,” but whose value will be recognized by closer analysis or using a non-standard theoretical approach.
However, one should not exaggerate the theoretical workload of observations. In the Müller-Lyer illusion, the line ending with arrowheads pointing outward appears to be shorter than an equally long line with arrows pointing inward.
Arrow illusion.
However, even when we know for sure that these two lines are the same length, our perception remains unchanged and the illusion remains. Likewise, a scientist with sharp eyes can notice something in the data, even if the theory says there is nothing in it. And if only one scientist sees something important, pretty soon every scientist in the field will know about it.
In their search for extraterrestrial life, scientists must be completely open-minded. And that means a certain amount of research on non-mainstream ideas and methods. Examples from past science show that non-core ideas can sometimes be severely held back. Space agencies such as NASA must learn from such cases if they truly believe that we should “expect the unexpected” in our search for alien life.