The Anthropic Principle and
Cosmic Inflation

1. Introduction

Citation Information

Allan, Leslie 2015. The Anthropic Principle and Cosmic Inflation, URL = <>.


It appears our universe is 'fine tuned' for life. With just a minor variation in some physical laws and constants, life, it seems, would be rendered impossible. In this essay, I will look at some of these key features and explore their significance for cosmology. I will examine what the Anthropic Principle has to say about our role as observers and the kind of universe we should expect to see. I will also explore the implications of modern cosmology and, in particular, inflation theory for the notion that the universe is built with our evolution in mind.

Some scientists and commentators have argued that there are many apparently incidental features about the universe that cannot differ from what we observe without it being impossible for life on earth to germinate and survive.

Such apparent 'fine-tuning' includes the following:[1]

  • If the strong nuclear force were 2% stronger, atoms would not have formed out of quarks. If it was 5% weaker, all atoms other than hydrogen would not have formed. This would have prevented the emergence of hydrogen-burning stars and deprived living things of hydrogen-based water.
  • If electromagnetic forces were marginally different, stars would not have produced the amount of carbon needed to allow life to evolve.
  • If space was not three-dimensional, planetary orbits would not be stable, making the evolution of life extraordinarily unlikely.
  • Gravity is some 1040 times weaker than the electrical forces. If the strength of gravity were only 100 times stronger than it is, the universe would not have existed long enough for stars and planets to form.
  • If the cosmological constant (dark energy) were an order or magnitude larger, galaxies would unlikely form.

The Anthropic Principle illuminates how we should deal with this apparent sensitivity of the cosmic constants to change. It is to this that I will now turn.


  1. [1] See, for example [Craig 1990; Davies 2004]

Copyright © 2015

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