Então, pergunta-se aqui, no Economist:
Porque é que os humanos não conseguem encontrar no universo sinais alienígenas?
Porque o esforço feito até agora é comprável com a tentativa de encontrar um peixe num copo de água mergulhado ao acaso no oceano, ou, mais esperançosamente, numa banheira.
Correl. - EXPLICAÇÃO EXTRA-TERRESTRE DA SALVAÇÃO DA TERRA
Correl. - EXPLICAÇÃO EXTRA-TERRESTRE DA SALVAÇÃO DA TERRA
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Why have humans never found aliens?
Perhaps they haven’t been looking hard enough
“IF ALIENS are so likely, why have we never seen any?” That is the Fermi Paradox—named after Enrico Fermi, a physicist who posed it in 1950.
Fermi’s argument ran as follows. The laws of nature supported the emergence of intelligent life on Earth. Those laws are the same throughout the universe. The universe contains zillions of stars and planets. So, even if life is unlikely to arise on any particular astronomical body, the sheer abundance of creation suggests the night sky should be full of alien civilisations. Fermi wondered why aliens had never visited Earth. Today, the paradox is more usually cast in light of the inability of radio-telescope searches to detect the equivalent of the radio waves that leak from Earth into the cosmos, and have done for the past century.
Thinking
up answers to this apparent contradiction has become something of a
scientific parlour game.
Perhaps life is really very unlikely. Perhaps
the priests are right: human beings were put on Earth by some creator
God for His own inscrutable purposes, and the rest of the universe is
merely background scenery. Perhaps there are plenty of aliens, but they
have decided that discretion is a safer bet than gregariousness. Or
perhaps galactic society avoids communicating with Earth specifically.
One chilling idea is that technological civilisations destroy themselves
before they can make their presence known. They might blow themselves
up after inventing nuclear weapons (an invention that, on Earth, Fermi
had been part of), or cook themselves to death by over-burning fossil
fuels.
In a paper published last month on arXiv,
an online repository, a trio of astronomers at Pennsylvania State
University have analysed the history of alien-hunting and come to a
different conclusion. In effect, they reject one of the paradox’s main
pillars. Astronomers have seen no sign of aliens, argue Jason Wright and
his colleagues, because they have not been looking hard enough.
Dr
Wright’s argument echoes that made by another astronomer, Jill Tarter,
in 2010. Dr Tarter reckoned that decades of searching had amounted to
the equivalent of dipping a drinking glass into Earth’s oceans at random
to see if it contained a fish. Dr Wright and his colleagues built on Dr
Tarter’s work to come up with a model that tries to estimate the amount
of searching that alien-hunters have managed so far. They considered
nine variables, including how distant any putative aliens are likely to
be, the sensitivity of telescopes, how big a portion of the
electromagnetic spectrum they are able to scan and the time spent doing
so. Once the numbers had been crunched, the researchers reckoned
humanity has done slightly better than Dr Tarter suggested.Rather than dipping a drinking glass into the ocean, they say, astronomers have dunked a bathtub. The upshot is that it is too early to assume no aliens
exist. Fermi’s question is, for now at least, not a true paradox.
This article appeared in the Science and technology section of the print edition under the headline "Where is everybody?"
