A paper published in the International Journal of Astrobiology argues that life on distant Earth-like planets is far more likely than previously thought.
What is the probability of abiogenesis, or life arising from inorganic substances, occurring elsewhere, given the existence of life on Earth? Scientists, and anyone else inclined to ponder about it, have been baffled by that question for a long time. In 1600, the Italian philosopher Giordano Bruno was burned alive as a heretic for saying that the universe has no center and that stars are suns, surrounded by planets and moons. Hence, he outlined some of the most important aspects of our cosmology. Copernicus and Kepler had mistakenly believed that the universe was spherical, the sun was its center, unmoving, and stars were not suns surrounded by planets. But what is perhaps even more important is that Bruno said that the worlds that likely exist elsewhere in the universe could support life on their own, an idea known as cosmic pluralism.
Brandon Carter, an Australian-born astrophysicist, contends that our existence puts constraints on what we can observe. On the basis of this knowledge alone, it is impossible to infer the probability of life elsewhere since abiogenesis had to happen on a planet. He concluded that life on Earth has a neutral value at best. In another way, because Earth was not randomly chosen from the set of Earth-like planets, it can’t be thought of as a typical Earth-like planet. Whitmire, a retired astrophysicist from the University of Alberta who teaches mathematics, argues Carter used faulty logic in a research paper.
As widely accepted as Carter’s theory is, Whitmire asserts that it suffers from what Bayesian confirmation theory refers to as ‘the old evidence problem,’ which updates a theory or hypothesis based on newly available evidence. After presenting some examples of how this formula is used in probability calculations and what role old evidence plays, Whitmire discusses his conception analogy. The author explains, “One could argue like Carter that I exist regardless of whether my conception was difficult or easy, and so my existence cannot tell us anything about my conception.” In this analogy, “hard” refers to contraception being used. The term “Easy” refers to the lack of contraception being used. Each proposition is given a value by Whitmire.
Whitmire continues, “However, my existence is old vidence and must be treated as such. When this is done, it becomes clear that my conception was much easier. Similarly, abiogenesis is the same story. Life on Earth has existed for a long time, and just as with conception, abiogenesis is much more likely to be simple.” Thus, evidence of life on Earth is not irrelevant to establishing life on similar planets. It is therefore likely that life can emerge on other Earth-like planets, perhaps even on the recently discovered “super-Earth” planet, LP 890-9b, located 100 light years from us. To date, astronomers have confirmed the existence of 5171 exoplanets, and there are 8933 distant alien worlds still awaiting confirmation. Based on our best estimates, astronomers think there are anywhere between 100 and 300 billion planets in the Milky Way galaxy alone.
Whitmire’s paper, “Abiogenesis: The Carter Argument Reconsidered,” was published in the International Journal of Astrobiology.