{"id":19470,"date":"2016-02-07T19:40:41","date_gmt":"2016-02-07T11:40:41","guid":{"rendered":"https:\/\/wp-productionenv-bjg9h2g2bgg5b8aa.southeastasia-01.azurewebsites.net\/news\/why-havent-we-found-aliens-heres-the-bad-news-and-the-good-news\/"},"modified":"2016-02-07T19:40:41","modified_gmt":"2016-02-07T11:40:41","slug":"why-havent-we-found-aliens-heres-the-bad-news-and-the-good-news","status":"publish","type":"post","link":"https:\/\/starpath.global\/news\/why-havent-we-found-aliens-heres-the-bad-news-and-the-good-news\/","title":{"rendered":"Why haven\u2019t we found aliens? Here\u2019s the bad news, and the good news"},"content":{"rendered":"
\"Jill
SETI pioneer Jill Tarter pays a visit to the Allen Telescope Array in California, one of the prime sites for the search for extraterrestrial intelligence. (Credit: SETI Institute)<\/figcaption><\/figure>\n

It\u2019s a question that goes back decades: If other civilizations have arisen beyond Earth over the course of billions of years, why haven\u2019t we heard from them? Two kinds of answers have recently come into the spotlight \u2013 one kind that\u2019s disheartening, and another kind that\u2019s challenging.<\/p>\n

First, the bad news: Researchers from the Australian National University say climate change could have killed off E.T. and his ilk.<\/p>\n

<\/span> The vast majority of life in the universe is either young and microbial, or extinct.<\/span><\/p>\n

In a paper published last month in the journal Astrobiology, Aditya Chopra and Charles Lineweaver suggest that habitable Earthlike planets eventually fall prey either to runaway global warming, as in the case of Venus; or runaway global cooling, as in the case of Mars.<\/p>\n

Their model proposes that if life ever does arise on an alien world, it would go extinct in most cases after just 1.5 billion years of the planet\u2019s existence, without getting past the microbial stage.<\/p>\n

Less than 10 percent of the habitable planets, including Earth, would pass through a \u201cGaian bottleneck.\u201d That means life progresses to the point at which it controls its own planetary environment. On Earth, for example, plant and animal forms of life are in a balance to keep water, carbon dioxide and oxygen at life-sustaining levels.<\/p>\n

Even in those cases, the Gaian bottleneck model shows life fading away after about 6 billion years, due to an increase in stellar luminosity for sunlike stars. (We\u2019re at the 4.6 billion-year point here on Earth.)<\/p>\n

\"Aditya
Astrobiologist Aditya Chopra says life forms on other planets would commonly die out due to runaway heating or cooling on their home planets. (Credit: Stuart Hay \/ ANU)<\/figcaption><\/figure>\n

Chopra and Lineweaver say the Gaian bottleneck could provide one of the answers to Fermi\u2019s Paradox \u2013 that is, if the universe is conducive to the rise of life, \u201cwhere is everybody?\u201d It could also explain why the search for extraterrestrial intelligence, or SETI, has come up short after nearly 60 years of looking.<\/p>\n

\u201cIf it takes several billion years to develop radio telescopes, then the Gaian bottleneck ensures that the vast majority of life in the universe is either young and microbial, or extinct,\u201d the researchers write.<\/p>\n

<\/span> No one would decide that the ocean was without fish on the basis of one glass of water.<\/span><\/p>\n

Before you get too depressed at that thought, consider the perspective of Jill Tarter, a pioneer in SETI research who helped inspire the character of Ellie Arroway in the Carl Sagan book (and Jodie Foster movie) \u201cContact.\u201d Tarter holds the Bernard Oliver Chair at the SETI Institute\u2019s Center for SETI Research, and recently talked with TechCrunch about the search for alien signals.<\/p>\n

The way Tarter sees it, the search has only just begun. Here\u2019s the way she explained it in a TED talk: \u201cAll of the concerted SETI efforts over the last 40-some years are equivalent to scooping a single glass of water from the oceans, and no one would decide that the ocean was without fish on the basis of one glass of water.\u201d<\/p>\n

More fundamentally, the search is limited by our imagination. We\u2019re still merely looking for the kinds of signals that we would send out if we were a super-advanced civilization \u2013 that is, radio and laser semaphore messages.<\/p>\n

\u201cWe may not have invented the right way to do this yet,\u201d Tarter told TechCrunch.<\/p>\n