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The Fermi paradox is the contrast between the likelihood of life existing elsewhere in the universe and the lack if evidence for it.

This is a significant conundrum. On the one hand, there is a strong sense that the conditions on Earth that led to the emergence of life cannot be unique. This makes it seem likely that life must be common.

But on the other, astronomers have scoured the cosmic haystack for the needle that would represent signs of intelligent life elsewhere in the universe and come up with nothing. As a result, many observers have concluded that there are no obvious signs.

Others disagree. Back in 2010, the astronomer Jill Tarter and colleagues argued that alien radio beacons could be obvious and common in our galaxy but that astronomers would not know because their searches have been incomplete.


These searches, said Tarter and co, are like searching a drinking glass of seawater for evidence of fish in all Earth’s oceans.


That’s a colorful metaphor, but given the considerable effort put into the Search for Extra-Terrestrial Intelligence (SETI), how accurate is it?


Today, we get an answer thanks to the work of Jason Wright and colleagues at Pennsylvania State University. These guys have characterized the parameter space that astronomers need to search for signs of alien life. They say this space is so vast that SETI searches so far have done little more than scratch the surface.


Wright and co’s method is straightforward. They begin by creating a mathematical model of the search space astronomers need to explore and then calculate what fraction has been investigated so far.

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