How to compute the odds that claims of extraterrestrial life discovery are real and reliable
The Search for Extra-Terrestrial Intelligence (SETI) has to be the most interesting field of science that lacks a subject to study. Yet. Keep searching. In the meantime, is there some metric we can apply to calculating the probability and impact of claims of such a discovery? There is.
In January, 2011 the Philosophical Transactions of the Royal Society published 17 articles addressing the matter of “The Detection of Extra-Terrestial Life and the Consequences for Science and Society,” including one by Iván Almár from the Hungarian Academy of Sciences and Margaret S. Race from the SETI Institute, introducing a metric “to provide a scalar assessment of the scientific importance, validity and potential risks associated with putative evidence of ET life discovered on Earth, on nearby bodies in the Solar System or in our Galaxy.” Such scaling is common in science—the Celsius scale for temperature, the Beaufort scale for wind speed, the Saffir-Simpson scale for hurricane strength, and the Richter scale for earthquake magnitude. But these scales, Almár and Race argue, fail to take into account “the relative position of the observer or recipient of information.” The effects of a 7.1 earthquake, for example, depends on the proximity of its epicenter to human habitations.
An improvement may be found in the Torino Scale that computes the likelihood of an asteroid impact and the risk of its potential damage—from 1, a near miss with no danger, to 10, certain impact with catastrophic consequences. But Almár and Race note that “the scale does not include any consideration of the observations’ reliability.” Building on SETI’s Rio Scale for evaluating the effect on society of an ET discovery, Almár and Race propose the London Scale that multiplies Q x δ, where Q (scientific importance) is the sum of four parameters:
- life form (1–5, from Earth-similar life to completely alien),
- nature of evidence (1-6, from indirect biomarkers
to obviously organized complex life),
- type of method of discovery (1–5, from remote sensing
to return mission sample), and
- distance (1–4, from beyond the Solar System to on Earth).
This sum is then multiplied by δ (a reliability factor) ranging from 0.1–0.5, from probably not real to highly reliable. The maximum Q can be is 20 x .5 = 10.
For example, Almár and Race compute the odds that the Allan Hills 84001 Martian meteorite contains alien life as (2+2+4+4)0.3 = 3.6 for scientific importance and credibility, noting that “several scientific counter-arguments have been published and the discovery has not been generally accepted.” I would assess the recent claim of arsenic-based life in Mono Lake as (2+1+4+4)0.2 = 2.2, fairly low by comparison.
Such scientific scales attempt to bring some rigor and reliability to estimates of events that are highly improbable or uncertain. The process also reveals why most scientists do not take seriously UFO claims. Although the first two categories would yield a 5 and a 6 (completely alien and complex life) and its distance is zero (4, on Earth), the method of discovery is highly subjective (perceptual, psychological) and open to alternative explanation (1, other aerial phenomena) and the reliability factor δ is either obviously fake or fraudulent (0) or probably not real (0.1), and so Q = (5+6+1+4)0.1 = 1.6 (or 0 if δ = 0).
The Phoenix lights UFO claim, for example, was a real aerial phenomena witnessed by thousands on the evening of March 13, 1997. UFOlogists (and even Arizona governor Fife Symington) claim it was extraterrestrial, but what is δ for this event? It turns out that there were two independent aerial events that night, the first a group of planes flying in a “V” formation at 8:30 that started a UFO hysteria and brought people outdoors with video cameras, which then recorded a string of lights at 10:00 that slowly sank until they disappeared behind a nearby mountain range. These turned out to be flares dropped by the Air National Guard on a training mission. Ever since, people have conflated the two events and thereby transmogrified two IFOs into one UFO. So δ = 0 and Q shifts from 1.6 to 0, which is how much confidence I have in UFOlogists until they produce actual physical evidence, the sine qua non of science.