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Two weeks ago, I wrote about the Copernicus Principle, which states that the Earth is an ordinary planet moving around the sun. After the publication of his book by Copernicus in 1543, it was quite logical to elevate this notion to the rank of principle. (In reality, the live action began much later, with Galileo and Kepler in the first two decades of the 1600s.) The movement was to move the Earth from its primordial position of cosmic centrality, which combined bad astronomy with Judeo-Christian theology: The Earth is as important as we are – created in the image of God and exercising dominion over the Earth, its creatures and its lands. The Copernican displacement was at the heart of the scientific revolution and the Enlightenment (although the latter spearheaded the notion of moral and intellectual superiority of the Western white man).
If we limit the Copernican Principle to a statement that Earth is not a special planet in terms of its location in the universe, then all is well. The problems start when we extrapolate to statements about the ubiquity of life in the universe, following the mistaken notion that if Earth is not special, neither is life. This is a massive non-sequitur. It becomes exponentially absurd when elevated to the so-called principle of mediocrity: since there is life on Earth and Earth is not a special place, life should be abundant in similar planets. to Earth around the universe, including intelligent life. In other words, the principle states that life is so abundant there that it is a poor property of the universe. This kind of thinking is not only bad science but also bad philosophy, and it has serious repercussions on our current project of civilization. If our planet and the abundant life it contains are so insignificant to the point of being mediocre, why respect either?
But first, the good stuff in principle. In general, if you have many samples of different objects, some in greater number than others – for example, balls of different colors in a large box, but most are red balls – there are strong chances that you have a higher probability of drawing a ball red compared to other colors. In this example, the red balls are mediocre because the most common. It seems pretty obvious.
In astronomy, the principle can be useful. For example, Isaac Newton and Christiaan Huygens applied it in the 17th century to estimate distances to stars, especially Sirius. If we assume that all stars are essentially identical (hence “mediocre†in the sense that all are equal), then their distances can be estimated by the differences in their luminosity: the farther the star is, the more it is. is weak from us, with a decrease in power with the square of the distance. While clearly flawed (the stars certainly aren’t the same), it was a good rough guess to get the ball rolling.
But stellar luminosity is very different from life. The principle of mediocrity implies that Earth-like environments are common and, by extension, life too. However, the stages from non-life to life, still completely unknown, cannot be considered as a direct consequence of Earth-like environments. A planet can have the right properties for harboring life – the right chemical composition, the right distance from the main star, the atmosphere, the magnetic field, etc. – and there would still be no guarantee that life would exist there. The fundamental error when applying the principle of mediocrity to estimate the ubiquity of life in the universe is its starting point: to assume that the Earth and its properties, including the existence of life here, are typical.
Quite the contrary: a quick glance at our neighbors in the solar system should dispel this notion. Mars is a frozen desert; though he had life in his early years, he did not offer enough stability to endure it for very long. The same goes for Venus, now infernal furnace. Further on, there are many “Earth-like” exoplanets, but only in the sense that they have similar mass and orbit a star at a distance that is in the habitable zone, where water, if it is present on the surface, is liquid. These prerequisites for life are far from life itself. It is not enough that life is simply possible in another world. Life has to be possible and have been around for a long time to have any chance of impacting the atmospheric makeup of the planet to be detectable tens, hundreds, or thousands of light years away. Thus, a planet must not only be able to generate life, but also to make it viable for hundreds of millions or billions of years.
So are the expectations of intelligent life elsewhere. Going from single-celled creatures to intelligent creatures takes unfathomable time. Natural selection is not a quick process and depends on a series of exogenous factors that vary from planet to planet. This requires that the planet provide climatic and geochemical stability, and that its mother star not be a potent producer of deadly ultraviolet radiation. There is nothing mediocre about this set of properties. Applying the principle of mediocrity to the study of life in the universe is a poor move based on faulty reasoning.
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