In recent decades, various phenomena have sparked scientific speculation about potential signs of extraterrestrial life. Two recent examples, the interstellar object 'Oumuamua and phosphine on Venus, raised hopes of alien origins but were met with alternative explanations. While these cases are just among many, most have ultimately had non-alien interpretations.
So, how can scientists confidently reach the correct conclusion when dealing with subtle indicators like a specific gas or an unusual celestial object? In a recent study, titled "Confidence of Life Detection: The Problem of Unconceived Alternatives" published in the journal Astrobiology, researchers introduced an approach to systematically assess such evidence with confidence.
How to Recognize Potential Signs of Extraterrestrial Life: A Guide To Identifying Aliens
Identifying Extraterrestrial Life Using Bayes' Theorem
The term "possible" can be quite flexible, encompassing both highly unlikely scenarios and high-probability events. It's important to interpret claims like "It might be aliens!" in the context of their likelihood.
Within scientific discussions, the importance of accurately expressing confidence levels derived from evidence cannot be overstated, leading to the utilization of tools such as Bayes' Theorem for this specific objective.
In a hopeful scenario, the available evidence could be input into the Bayes formula, yielding a numerical output between 0 and 1, with 0.5 indicating a 50:50 probability of the signal being of alien origin.
However, although Bayesian analysis is valuable, it faces limitations in assessing the likelihood of extraterrestrial life. It depends on factors like the prior probability of alien existence and the probability of natural occurrences, which vary widely.
Some biosignatures, like a dinosaur skeleton, have low natural occurrence probabilities; but for others, such as certain gas blends, we lack sufficient knowledge.The challenge lies in "unconceived alternatives" or the possibility that undiscovered phenomena could explain observed signals, given humanity's limited research. We may not have explored all potential sources for these phenomena comprehensively.
New Approach in Detecting Aliens: CoLD and EURiCA
In 2021, a team associated with NASA introduced the Confidence of Life Detection (CoLD) framework that provides a structured approach with seven steps for validating discoveries, spanning from ruling out contamination possibilities to securing follow-up observations of anticipated biological signals within the same area.
Nevertheless, the ongoing challenge of unconceived alternatives remains a significant hurdle. The framework's Level 4 stipulates the necessity to establish implausibility for "all recognized non-biological sources of signals," a requirement that becomes meaningful only after an exhaustive exploration of potential alternatives.
A novel proposal from the Exploring Uncertainty and Risk in Contemporary Astrobiology (EURiCA) group draws inspiration from the Intergovernmental Panel on Climate Change (IPCC). The IPCC has effectively employed a framework for decades that integrates the quantity and quality of evidence with expert consensus to convey confidence levels in climate change assertions.
This framework could be adapted for the detection of extraterrestrial life, with experts evaluating evidence based on both scientific merit and consensus within the scientific community.
The assessments would range from weak, indicating limited expert consensus and evidence, to strong, denoting high consensus and substantial evidence. By conducting comprehensive explorations of relevant possibilities, astrobiologists can enhance their capacity to confidently identify extraterrestrial life while minimizing the chances of alternative explanations emerging.
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