PARIS — Ever heard of the Fermi paradox? In 1950, in Los Alamos, New Mexico, Enrico Fermi, the famed Italian physicist and father of the first nuclear reactor, estimated the probability of the existence of extraterrestrial civilizations in the Milky Way, based on the number of stars in our galaxy with a planetary system gravitating around them.

Physicist Mathieu Agelou wrote about the "paradox" in the introduction to a book on aliens recently published by the French National Center for Scientific Research.

“The percentage among those planets ... likely to host life, (and) the probability of life appearing when the conditions of its appearance are met — and finally that among these life forms that a civilization of intelligent beings would appear that have the desire and technological means to explore the universe.” Even with the most conservative assumptions, Fermi was ultimately left with a very large number of extraterrestrial civilizations that could indeed come visit us. But how, he asked, is it that we haven’t seen any sign of any of them yet?

All the progress made in astronomy since the beginning of the 1950s and, in particular, the discovery over the past 20 years of several thousand exoplanets, have only reinforced the paradox. It can actually make you feel quite pessimistic about the sustainability of the human species on planet Earth: If we haven’t heard from any extraterrestrial life form, it may be that no technologically advanced civilization out there has lasted long enough to have time to explore other galaxies. Or that no development model has been able to protect its natural base, its resources, its civil peace long enough. This hypothesis is now seriously taken into consideration and studied by researchers from different fields — economics, ecology, sociology.

The invention of the steam engine comes two-thousandths of a second before the fateful midnight.

As far as the Earth is concerned, U.S. geographer and biologist Jared Diamond's book Collapse explores the causes of human civilizations vanishing in the past, including the inhabitants of Easter Island, the Mayan society of Central America, and the Vikings of Greenland. Might we, Diamond posits, also be rushing towards our own destruction?

Back at the dawn of the Industrial Revolution, humankind brought its terrestrial cockpit into a new geologic time, the Anthropocene. For the first time since its appearance 300,000 years ago in Africa, Homo sapiens had become a major geologic force. Looking at the entire history of our planet as a period of 24 hours, the invention of the steam engine comes two-thousandths of a second before the fateful midnight.

Might we be rushing towards our own destruction? — Photo: Dick Duckhorn

Will the arrival of the industrial age bring about the end of humanity? Eloquent charts offer such scenarios: sudden acceleration of the rate of extinction for species (to the point that scientists now speak of a sixth extinction, the fifth having been the one that killed the dinosaurs 65 million years ago), rampant artificialization of ecosystems, soaring global energy consumption (multiplied by at least 40 between 1800 and 2000 while, at the same time, the world population was multiplied by only six).

Established a dozen years ago by the climatologist William Steffen, the dashboard of the “Earth system,” with its 24 parameters ranging from greenhouse gas emissions to the number of tons of fertilizer poured into the soil, all of which present the same general outlook — a surge between 1750 and 2000 — have become the standard bearer of "anthropocenologists." It has served as a starting point for many scientific studies that all sound the same alarm. One of the most resounding, published in 2009 in Nature magazine, introduced in the scientific literature the notion of "Planetary boundaries," those vital limits not to be exceeded if humankind wants to continue to benefit from an ecosystem that is fundamentally stable and safe.

The study’s main authors, Johan Rockström, the director of the Stockholm Resilience Center, and William Steffen himself, identified nine such boundaries. At the time of the study, two of these nine had not yet been quantified due to the lack of data (chemical pollution and atmospheric aerosol loading), four had not yet been crossed (land-system change, freshwater use, stratospheric ozone depletion and ocean acidification) and three were already crossed: global warming due to greenhouse gases emissions, the erosion of biodiversity and the disruption of the biogeochemical cycles of nitrogen and phosphorus, resulting in particular from intensive agriculture and livestock farming.

It may, therefore, be necessary, one day, to colonize other planets, once this one will have become uninhabitable.

The fundamental message from all these scientists is that Earth can and should be seen as a complex system. Its behavior is not predictable because, between causes and consequences, the linearity principle doesn’t always prevail. Small factors can have gigantic consequences. Beyond a certain point, the machinery can spin out of control. With its current development model — extremely destructive and ineffective — humankind is now playing with existential fire. “The eternal silence of these infinite spaces” that so terrified Blaise Pascal does not seem to encourage human beings to alter their behavior.

It may, therefore, be necessary, one day, to colonize other planets, once this one will have become uninhabitable. This is the starting scenario of a disturbing number of recent novels and films. We know that the visionary entrepreneur Elon Musk is preparing the colonization of Mars. But Hollywood has also given us a taste of how that planet's ecosystem is indeed a long way from ideal for humans to thrive, or even just survive.