While we wait for concrete, verifiable evidence of the existence of advanced extraterrestrial civilizations, we must be content with determining the probability of such intelligent beings and the chances that we have or will encounter them. These types of mathematical exercises have given us the Drake equation, named for the recently passed Frank Drake, whose formula to estimate the number of active, intelligent civilizations in just the Milky Way galaxy is dependent on variables that are difficult to determine precisely and thus generates an approximation rather than an exact number. The Fermi paradox -- in which Enrico Fermi looks at the probability of life forming easily on other planets and asks, if it is so easy, “Where are they?” – was a mathematical exercise among his fellow physicists.
The Great Filter, introduced by economist Robin Hanson, looks at the low probability of abiogenisis – the idea that life can evolve from chemical processes on inanimate matter – and determines that it could occur on any Earth-like planet given enough time. Theoretical physicist Brandon Carter disagrees with the Great Filter – he proposed that abiogenesis on Earth does not make it any more or less likely to occur on other planets … and that Earth may be the only planet in the universe with life on it. That brings us to Daniel Whitmire, an astrophysicist and mathematics professor at the University of Arkansas. In a new paper published in the International Journal of Astrobiology, Whitmire uses mathematics to attack the Great Filter hypothesis – one that he himself accepted until recently.
“The Conception analogy stuck in my mind and ultimately I came to believe that the Carter argument must be wrong. But at that point I didn't know why it was wrong.”
In a University of Arkansas press release, Whitmire explains the inspiration for his own hypothesis came from the most unlikely of places for inspiration these days – an anonymous commenter on another of his papers. That person compared abiogenesis to human conception in terms of being easy or difficult. In his first analysis, Whitmire follows the path of the Great Filter and concludes that “I exist regardless of whether my conception was hard or easy, and so nothing can be inferred about whether my conception was hard or easy from my existence alone.” A “hard” conception in Whitmire’s analysis means contraception was used. However, the key element in this case is not the conception but the existence of Whitmire himself.
“However, my existence is old evidence and must be treated as such. When this is done the conclusion is that it is much more probable that my conception was easy. In the abiogenesis case of interest, it's the same thing. The existence of life on Earth is old evidence and just like in the conception analogy the probability that abiogenesis is easy is much more probable.”
The term “old evidence” refers to something called “The Old Evidence Problem” in the Bayesian Confirmation Theory – that theory deals with what to do with old evidence when new data is acquired for an existing hypothesis. Vice does a good job in simplifying both of these complex ideas. With The Great Filter, Carter says that old evidence – in this case, the existence of life on Earth -- has no influence on the probability of its occurrence elsewhere. Whitmire, using the contraception argument, disagrees – conception is ‘easy’, therefore his own existence is easy. Similarly, the probability of life on earth via abiogenesis is also more likely to have been ‘easy’, therefor the existence of life on other planets is also ‘easy’ … especially on other Earth-like planets. But potentially even on planets that are only similar but in the habitable or so-called ‘Goldilocks’ zone of their star.
For the mathematically inclined, Whitmire’s paper gives mathematical formulas for Carter’s argument and how it applies to simple probability exercises like coin tosses or a more complex exercise involving urns willed with differing numbers of balls and coin tosses to determine from which one balls are removed. He then gives a formular for abiogenesis using the ‘conception analogy’ and concludes that there is a good possibility that abiogenesis will occur sometime during the habitable lifetime of an Earth-like planet based on “the fact that life on Earth constitutes old evidence and it should be evaluated in that context, and the application of an independent time-scale argument to determine the Bayesian prior probabilities.”
Now that he has a mathematical formula to support his argument that life exists on planets other than Earth, will other scientists line up outside of Daniel Whitmire’s door to pat him on the back? Will the “Where are they” question of Fermi’s paradox finally be solved? Will Drake’s equation need to be revised? Whitmire isn’t holding his breath on the possibility of any of these happening … and he gives a very good reason why.
“My opinion is that what many scientists believe about life and intelligent life in the universe is almost political or psychological. If they want to believe life is rare they will point to the Carter argument or some other argument, like the statistical improbability of abiogenesis, to make their case.”
Politics! Until that old bugaboo – concrete evidence – is found via telescopic observation, eyewitnessing by astronauts or a verifiable visit by ETs to Earth, Whitmire believes scientists will stick to their preconceived notions on the existence of life that are based on politics, psychology or even religion. His interview with Vice points out that the probability of new evidence arriving soon is good – we have NASA’s Perseverance rover roving across Mars and digging in the soil for signs of ancient life. We have the future missions planned to two moons in our solar system which may be habitable -- Jupiter’s Europa and Saturn’s Enceladus. And we have the hot new James Webb Space Telescope spitting out fabulous photos of other star systems and other galaxies – the focus of these photos will soon be narrowed to look for biosignatures, technosignatures and other signs of life on exoplanets. Just one shred of evidence of abiogenesis would give Danial Whitmire something that neither Fermi nor Drake not any other scientist in history has – validation.
“If life (or past life) were found anywhere in our solar system or beyond that would statistically guarantee that the origin of life is very easy and life can be expected to be abundant throughout the universe. That's why so much effort is being put into missions to Mars and ultimately Europa, and elsewhere. If life is easy, then the James Webb telescope may find extrasolar planetary biosignatures in the not-too-distant future.”
Don’t let the politics get you down, Daniel!