The anthropic planet

Michel Claessens

Welcome to planet Earth! This special issue, published on the occasion of the International Year of the Planet Earth 2008, is devoted entirely to the third planet from the Sun - our very own home sweet home.

You will notice that this issue makes virtually no mention of the development of life on Earth - a phenomenon that radically changed the face of our planet and the history of our species. This is an editorial choice that some may contest as our planet is inextricably linked to the life that inhabits it. The Earth is in fact a living and ever-changing entity. The scientist James Lovelock describes our planet as a living organism in what he formulated as the Gaia hypothesis. Like biological organisms, Gaia regulates the concentration of its principal "metabolites", in this case the atmospheric gases.

Life is also inextricably linked to the Earth in the sense that if the Earth had been just slightly different we would not have been here to talk about it. Without its liquid core, and thus without the magnetic field that it generates and that protects us from cosmic rays, life would not have been able to survive or even exist at all. Without the very particular characteristics of our planet (its radius, spherical shape, distance from the Sun, composition, etc.) there would have been no earthquakes but no life either! This is in fact a very "down to earth" version of the famous "anthropic" principle dear to cosmologists that states that the Universe possesses very special physical characteristics, as if chosen to preside over the birth of life. The Universe would have thus been created to observe itself! Notably through the pages of this magazine...

Michel Claessens
Editor in chief