The Anthropic Principle and
Cosmic Inflation

2. The Anthropic Principle

Book cover: The Biological Mind: A Philosophical Introduction by Justin Garson

The term Anthropic Principle was coined by an Australian physicist, Brandon Carter, in his [1974] article[2] that first appeared in Confrontation of Cosmological Theories with Observational Data. In it, Carter countenanced against overreaction to the Copernican Principle. This principle postulates that we do not occupy a privileged central position in the universe. Copernicus' challenge in the 16th century to the Ptolemaic view that our earth is stationary at the centre of the universe has been repeated in kind throughout the following centuries. Subsequent scientific advancements have revealed that the earth's geology, astronomy and cosmology occupies but a tiny corner of the universe in space and that our history is fleetingly short as judged against cosmic time. In the middle of the 19th century, Charles Darwin completed the dethronement of the human race by showing how our evolution and the evolution of all life on this planet is the result of blind physical forces.

Carter wanted to redress the balance by suggesting how our evolution and place in the universe limits the kinds of universe we can observe. His point with his Anthropic Principle was to show how the conditions we observe may be typical for any kind of observer but not typical for the entire universe.

He expressed this as his weak Anthropic Principle: 'our location in the universe is necessarily privileged to the extent of being compatible with our existence as observers.'[3] Using this principle, he predicted in retrospect the observed value of the cosmological constant to fall within a narrow band suitable for stars to form. Anthropic reasoning suggests that we should epistemically favour explanations in which our location as observers in space and time are unremarkable. The apparent 'fine-tuning' effects listed in the introduction above are then just anthropic effects of the kinds of observers we are.

Some advocates have put the case for a stronger version of the Anthropic Principle.[4] On these renditions of this stronger version, proponents have argued that the weak version entails that the conditions in the entire universe are compatible with the evolution of observers or even that such conditions are necessary. These stronger conclusions are unwarranted extrapolations from and misinterpretations of the weak Anthropic Principle.

Carter's weak version is not saying that the universe was intentionally set up for life to exist or that life is some kind of goal of the universe's existence. Contra the strong version, the evolution of life is not a necessary product of the universe. Such teleological hypotheses result from confused readings of the weak Anthropic Principle. The weak version is not saying that the reality of our existence in some way restricts the range of universes that could possibly exist, thereby ruling out as impossible those that could not support life. What it is saying is that given that observers exist, this restricts the range of observed universes to those that support the evolution of life.

The Anthropic Principle suggests that the universe we observe may be but a tiny part of a very much bigger universe in which the physical conditions and laws are different in other locations compared with those in our own locality. Inflation theory in modern cosmology lends a theoretical underpinning and experimental support to this idea.


  1. [2] To remove the bias towards the male gender and the human species, the principle is also later referred to as the Biophilic Principle.
  2. [3] [Carter 1974: 291]
  3. [4] For a comprehensive review and argument, see [Barrow and Tipler 1986]

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