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Back in 1974, the American astronomer Michael Hart published a paper in the Quarterly Journal of the Royal Astronomical Society entitled “An Explanation For The Absence Of Extraterrestrials On Earth”. In it, he pointed out that there are no intelligent beings from outer space on Earth now, a statement that he famously referred to as Fact A.

“Fact A, like all facts, requires an explanation,” wrote Hart. He went on to conclude that Fact A is explained by the notion that intelligent life from outer space does not exist. In other words, we are alone in the galaxy.

Hart’s paper addresses the Fermi paradox named after the physicist in Enrico Fermi who famously asked: if intelligent aliens exist, where are they? Indeed, Hart’s arguments have become so famous that the problem is often called the Fermi-Hart paradox.

Today, Jason Wright at Pennsylvania State University and a few pals revisit Hart’s argument, it’s various rebuttals and many others associated with the Fermi paradox. In particular, they focus on the possibility that extraterrestrial civilisations would give themselves away by the waste heat generated by their activities. Therefore a useful way to search for extraterrestrial civilisations is to look for the infrared signature of this waste.

The basic problem with the idea that intelligent life exists elsewhere in the galaxy is that the Sun is an ordinary star and that there are many billions of others like it in the Milky Way. Many of these will have Earth-like planets orbiting them so there must have been ample opportunity for intelligent life to evolve elsewhere.

What’s more, if any of these civilisations had begun to explore the interstellar space around them, even at the very slow speeds that humans can manage, it would take only a few tens of millions of years to colonise entire galaxy.

So the fact that we do not see intelligent life out there must mean it does not exist. In other words, we are the first and we are alone.

Wright and co extend Hart’s argument to alien energy supplies. The basic idea here is any advanced civilisation would require vast amounts of energy and the most likely source of this energy is the star that it orbits. However this energy is used, it must inevitably end up as waste heat which ought to be visible in the infrared.

“We argue that detectably large energy supplies can plausibly be expected to exist because life has potential for exponential growth until checked by resource or other limitations, and intelligence implies the ability to overcome such limitations,” say Wright and co.

And they come to an odd conclusion. Wright and co say that if Hart’s thesis is correct, that we are alone in the galaxy, then searches for large alien civilisations in other galaxies may be fruitful. And if it is incorrect, then searches the civilisations within the Milky Way are more likely to succeed than Hart argued.

In other words, it is well worth continuing to look for extra-terrestrial civilisations. A curious argument but built on the back of a comprehensive review of the search for extra terrestrial civilisations and their energy supplies.

Well worth a read if you want a good review of the science in this area.

Ref: arxiv.org/abs/1408.1133  The G Infrared Search For Extraterrestrial Civilizations With ˆ Large Energy Supplies. I. Background And Justification

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