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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.

To read more, click here.