[I find that I’m getting excited by what I take to be cases of Inferences to Any Old Explanation, so I keep writing them up; some of these will end up in the chapter and some probably will.]
The loveliness, to use Lipton’s terminology, of a given explanatory hypothesis can depend on the interests of the epistemic agents who are considering a range of candidate explanations for some phenomena or event. In 2005 two astrobiologists, Chris McKay and Heather Smith, argued that a lack of hydrocarbons on the surface of Titan, one of the moons of Saturn, would lend support to the claim that there is extraterrestrial life in the oceans beneath Titan’s frozen surface. In 2010 a pair of studies were produced that confirmed that Titan had not just an uncharacteristic lack of both acetylene and hydrogen on its surface, but that it seemed to be being actively depleted. Some members of the public and the press took this as confirmation that life had been found on Titan because the particular phenomena of there being a lack of hydrocarbons on the surface of Titan was explained by the explanatory that methanogenic life was present there.
Now, the explanatory hypothesis that methanogenic life is present on Titan is a lovely explanatory hypothesis because it renders understandable the lack of certain hydrocarbons with respect to the thesis that life exists outside the Earth. However, the explanatory hypothesis, whilst likely, is not the most likely. As Chris McKay commented after the recent news reports about life on Titan:
The existence of methane-based life churning through hydrocarbons and gaseous hydrogen is the fourth most likely explanation out of four, according to McKay. “This is a still a long way from `evidence of life’,” he wrote. “However, it is extremely interesting.”1
Indeed, McKay believes the most likely explanation of the lack of hydrocarbons on the surface of Titan is that the determination that hydrocarbons travel to the surface of Titan is mistaken, with the second most likely explanatory hypothesis being atmospheric processes that transport hydrogen out of the upper atmosphere and the third most likely explanatory hypothesis being that non-biological chemistry at the surface is depleting the hydrocarbons.
Now, the presence of methanogenic life being present on Titan is a plausible contender, as an explanatory hypothesis, for the explanation of Titan’s uncharacteristic lack of hydrocarbons on its surface, but it is not the most likely contender. The other three candidate explanatory hypotheses are more likely and are just as lovely, as they, too, promote an understanding as to why there is a lack of hydrocarbons on Titan’s surface. However, we might forgive epistemic agents if they would prefer the explanatory hypothesis that methanogenic life is present on Titan because this explanatory hypothesis tells us something new and novel about the universe, which is that life exists outside the Earth. This might be, psychologically-speaking, a much lovelier explanatory hypothesis to the lay epistemic agent than, say, a geothermal explanatory hypothesis might be to the xeno-geologist. Given a choice between lovely explanatory hypotheses we might choose the one that appeals to us psychologically2. Now, this speaks to the tradeoff between likeliness and loveliness; according to McKay there are three more likely candidate explanatory hypotheses that explain the lack of hydrocarbons on Titan’s surface, all of which are, at least to the scientist, lovely. However, some members of the public and the press inferred to a lovely but not as likely an explanation; they committed an Inference to Any Old Explanation.
- For example, someone who believes life cannot exist outside of the Earth might think the explanatory hypothesis that the presence of methanogenic life being present on Titan is not lovely, or, at least, not as lovely as some other credible contender.↩