Vast, Cool and Unsympathetic: Other Worlds Detecting Earth

If aliens visited Earth in any numbers, the result would likely be a disaster for our species. This has been the consensus of the not-inconsiderable number of scientists who have given this topic serious thought, Stephen Hawking not least among them.

And yet, there are people who deliberately try to signal our presence to aliens. If you take the possibility of intelligent aliens seriously, you should support a ban on this activity. These people either don't seriously believe they'll be heard, or they're willing to risk the end of life on Earth at some future time, all for their little project. It's as if the Mayans had built signal fires on the beach to show the locations of their cities to any helpful people navigating the coast in giant canoes.

If you think life on Earth is the result of evolution, and for some reason you're hesitant to extend Darwinian principles to the rest of the universe, think about it this way:

• a) the Mayans encountered individuals from the same species, a mere four thousand years more technologically advanced than themselves, and the results were catastrophic to Mayan civilization and the New World's ecosystem, and


• b) any idea that humans are somehow nastier than any advanced organisms that might visit from the stars is based on nothing, except wishful thinking and a desire for moral signaling.

If you like Earth's ecosystem, and you despair of the way that invasive species from the Old World (for the most part) have rolled over those in the New World and on island ecosystems like New Zealand, imagine the damage to Earth's biomes from invasive alien microorganisms. (Again, if we take the possibility of aliens seriously, then this should be considered as low probability, very high consequence threat, i.e. an existential threat, along the lines of an asteroid impact or gamma ray burst.)

Therefore, it's worth worrying about how easy we are to detect. This paper proposes a way to cloak the Earth with lasers. Another way to think about it is to establish a detectability index, and a useful one might be: how far away could a parallel Earth (with the same EM emissions) be, for us to detect it? Or, for them to detect us? I call this the C-index, and XKCD's What If addressed the same question. Now, astronomers have asked what other solar systems are ideally positioned to witness a transit of Earth against the sun, even without hearing EM emissions.

Astronomers have debated what types of planets are most likely to develop life, and a good summary might be that we should like for habitable-zone super-Earths that are closer to the center of the galaxy and have had frequent proper motion close passes by other stars. We should see if any of these stars meet those conditions, and study them exhaustively.

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