Astronomy:Mediocrity principle

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The mediocrity principle is the philosophical notion that "if an item is drawn at random from one of several sets or categories, it's likelier to come from the most numerous category than from any one of the less numerous categories".[1] The principle has been taken to suggest that there is nothing very unusual about the evolution of the Solar System, Earth's history, the evolution of biological complexity, human evolution, or any one nation. It is a heuristic in the vein of the Copernican principle, and is sometimes used as a philosophical statement about the place of humanity. The idea is to assume mediocrity, rather than starting with the assumption that a phenomenon is special, privileged, exceptional, or even superior.[2][3]

Extraterrestrial life

The mediocrity principle suggests, given the existence of life on Earth, that life typically exists on Earth-like planets throughout the universe.[4]

Measurement of distance to stars

The mediocrity principle was implicitly applied during the 17th century, when astronomers attempted to measure the distance between distant stars and the Earth. By assuming that the Sun was just an average star, and that some stars seemed brighter simply because they were closer to us, they were able to estimate how far these stars were from the Earth. Although this method was flawed in view of the differences among stars, it gave astronomers at that time a rough idea of how far the stars were from the Earth. For example, James Gregory, Isaac Newton and Christiaan Huygens were able to estimate the distance between Sirius and the Earth through this method.[5]

Comparison with other approaches

The mediocrity principle is in contrast with the anthropic principle, which asserts that the presence of an intelligent observer (humans) limits the circumstances to bounds under which intelligent life can be observed to exist, no matter how improbable.[6] Both stand in contrast to the fine-tuning hypothesis, which asserts that the natural conditions for intelligent life are implausibly rare.

The mediocrity principle implies that Earth-like environments are necessarily common, based in part on the evidence of any happening at all, whereas the anthropic principle suggests that no assertion can be made about the probability of intelligent life based on a sample set of one (self-described) example, who are necessarily capable of making such an assertion about themselves.

It is also possible to handle the Mediocrity Principle as a statistical problem, a case of a single Data point statistics, also present in the German tank problem.

Other uses

David Deutsch argues that the mediocrity principle is incorrect from a physical point of view, in reference to either humanity's part of the universe or to its species. Deutsch refers to Stephen Hawking's quote: "The human race is just a chemical scum on a moderate-sized planet, orbiting around a very average star in the outer suburb of one among a hundred billion galaxies". Deutsch wrote that Earth's neighborhood in the universe is not typical (80% of the universe's matter is dark matter) and that a concentration of mass such as the Solar System is an "isolated, uncommon phenomenon". He also disagrees with Richard Dawkins, who considers that humans, because of natural evolution, are limited to the capabilities of their species. Deutsch responds that even though evolution did not give humans the ability to detect neutrinos, scientists can currently detect them, which significantly expands their capabilities beyond what is available as a result of evolution.[7][clarification needed]

See also


  1. Kukla, A. (2009). Extraterrestrials: A Philosophical Perspective. Lexington Books. p. 20. ISBN 9780739142455. 
  2. "principle of mediocrity - astrobiology". 
  3. "THE WORLD QUESTION CENTER 2011 — Page 12". 
  4. Chaisson, Eric, and Steve McMillan. Astronomy: A Beginner’s Guide to the Universe. Ed. Nancy Whilton. San Francisco: Pearson, 2010.[page needed]
  5. Gingerich, Owen (2006). God's Universe. Cambridge, Massachusetts: The Belknap Press of Harvard University Press. p. 20. 
  6. Anthropic Principle
  7. David Deutsch (2011). The Beginning of Infinity. ISBN 978-0-14-196969-5. 


  • Gonzalez, Richards, The Privileged Planet: How Our Place in the Cosmos is Designed for Discovery, Regnery Publishing, 2004, ISBN:0-89526-065-4
  • Peter Ward and Donald Brownlee, Rare Earth: Why Complex Life is Uncommon in the Universe, Copernicus Books, January 2000, ISBN:0-387-98701-0

External links