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SCIENCE AT WORK SPECIAL REPORT Fermi’s Paradox and the Missing Aliens FOCUS PROFILE LAB WATCH OPINION PORTFOLIO Astronomy. While our galaxy hosts billions of planets, it seems quite extraordinary that we have not had any contact with a single extraterrestrial civilization. Physicist Gabriel Chardin addresses this issue, commonly known as the Fermi paradox. I n the early 1950s, Nobel physicist Enrico Fermi pointed to an apparent paradox: considering that our galaxy, the Milky Way, is home to some 200 billion stars, and that there are most probably (as we now know with greater certainty) several hundred billion planets orbiting them, why have we not yet been visited by at least one extraterrestrial civilization? Even in the hypothesis that life exists on only a tiny fraction of those billions of planets, the shear size of our galaxy (about 100,000 light years across) means that a civilization like ours, which should soon be able to explore surrounding solar systems at an appreciable fraction of the speed of light, could possibly investigate a significant part of our galactic star system in less than a million years. This time frame is only about 1/10,000th of the age of our galaxy, which dates back some 13 billion years, or of the Universe, which is approximately 14 billion years old. It would therefore have been highly likely for our planet to be visited by several hundred different extraterrestrial species—so far conspicuously absent. A matter of time? Fermi, however, seems to have overlooked an important factor: the time it will take to exhaust our available resources, be it of our planet or even of the observable Universe (say within a radius of 10 billion light years, or about 100 quintillion kilometers). Based on the seemingly reasonable hypothesis of a 2% annual growth rate in the consumption and use of these resources, the Earth’s supplies should have run out in a few hundred years, with a wide margin of uncertainty. For the entire observable Universe, strangely, estimates are more accurate: roughly 5000 to 6000 years. This time span is absurdly short, and seems paradoxical, as it would normally take several billion years to exhaust all resources within a radius of 10 billion light years, unless a very large number of expansionist civilizations were at work simultaneously or had access to faster-than-light travel, which seems impossible. In other words, a 2% annual growth rate over a few millennia would almost certainly burn out any planetary system. More life means less stability In my opinion, this is the best response to Fermi’s paradox: life acts as a sort of accelerator, inducing high instability. For lack of an extremely precise and rigorous strategy, it is most probable that, like ants burrowing in a mound of gunpowder, we would be doomed as soon as we By Gabriel Chardin Physicist Gabriel Chardin chairs the committee overseeing the very large research infrastructures (TGIR) of the CNRS. He received the 2007 CNRS Silver Medal for his research on dark matter. From 2012 to 2014, he acted as deputy scientific director at the CNRS’s National Institute of Nuclear and Particle Physics (IN2P3) and is the former director of the interdisciplinary CSNSM laboratory1 in Orsay (near Paris). gabriel.chardin@cnrs-dir.fr © J.-F. DARS/CNRS PHOTOTHÈQUE 1. Centre de sciences nucléaires et de sciences de la matière (CNRS / Paris-Sud Université). 16 CNRS INTERNATIONAL MAGAZINE


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