Are aliens hard to find because they're extinct?
Evidence of extraterrestrial life may be hard to find because , a new study suggests.
Researchers Aditya Chopra and Charles Lineweaver, both of the Australian National University, recently published a paper in the journal 础蝉迟谤辞产颈辞濒辞驳测听suggesting that extinction could be the main cause of humanity鈥檚 fruitless search for extraterrestrials.
鈥淭he universe is probably filled with habitable planets, so many scientists think it should be teeming with aliens,鈥� said Mr. Chopra in a . However, Chopra and Dr. Lineweaver say that, despite the presence of livable sites, alien life may not have evolved quickly or well enough to sustain itself on various worlds.
鈥淓arly life is fragile, so we believe it rarely evolves quickly enough to survive,鈥� Chopra said. 鈥淢ost early planetary environments are unstable. To produce a habitable planet, life forms need to regulate greenhouse gases such as water and carbon dioxide to keep surface temperatures stable.鈥�
This conjecture, which Chopra and Lineweaver call a 鈥淕aian bottleneck,鈥� offers a different view on alien existence than previous similar ideas and provides an answer to the Fermi paradox 鈥� the conflict between the apparently high probability that alien life could evolve and the lack of any hard evidence demonstrating alien development.
The Gaian bottleneck conjecture submits that the overlap between a species' habitable conditions and its planet's actual conditions is usually very brief, and that most species die out before they can evolve or change their聽environment聽enough to match with both.
The new study also offers a different view on聽a concept first proposed by George Mason University economist Robin Hanson聽that suggests that science鈥檚 current perception of the process of basic evolution that eventually leads to intelligent life and cosmic colonization is wrong.
Prof. Hanson hypothesized that there is a step, , in the universal 鈥渆volutionary path鈥� that almost no species can successfully complete. 鈥淸S]o far nothing among the billion trillion stars in our whole past universe," he writes, "has made it all the way along this path.鈥澛�
The Great Filter suggests that humanity may be doomed to be filtered out at some point in the future, but Chopra and Lineweaver鈥檚 study goes in a different direction in saying that early life is somewhat responsible for making its environment habitable and in a way providing for its own evolution - indicating that humanity already passed through its filter.
This idea means that in most instances where life has existed, it has died; 鈥渆xtinction is the cosmic default,鈥� according to the researchers. It also means that if there was no life originally on a planet after its formation, it is very unlikely that place would ever see the presence of anything living; 鈥減lanets need to be inhabited to remain habitable.鈥� These two arguments are Chopra and Lineweaver鈥檚 answer to Fermi鈥檚 paradox and would explain why life is apparently so rare in the universe.
So it is possible that alien species existed all over the universe in environments conducive to life, but if humanity ever finds traces of them it鈥檚 likely to be in the form of fossilized, basic life forms that simply didn鈥檛 evolve rather than as evidence of sentient aliens with advanced civilizations.
鈥淥ne intriguing prediction of the Gaian Bottleneck model is that the vast majority of fossils in the universe will be from extinct microbial life, not from multicellular species such as dinosaurs or humanoids that take billions of years to evolve,鈥� said Lineweaver.
