How Would We Find Alien Life?

What we actually know

SETI has never searched the whole sky, continuously, across every wavelength, for every possible signal structure. It sampled particular frequencies, particular directions, particular signal shapes, at particular times. The honest summary is that we lowered a drinking glass into an ocean and found no fish in the glass. Meanwhile the positive results are real but indirect: thousands of confirmed exoplanets found by transits (a star dimming as a planet crosses it) and radial velocity (a star wobbling as a planet tugs it), and transmission spectroscopy that reads starlight filtered through an atmosphere for gases out of chemical equilibrium — oxygen with methane, for instance, which should destroy each other unless something keeps replenishing them.

Where the extrapolation begins

A biosignature is a statistical argument about chemistry, not a photograph of a creature. A technosignature is harder still: it requires the other side to be technological, detectable, close enough, and doing it now. Each of those is a separate filter, and multiplying uncertain fractions produces an answer with an uncertainty far wider than the answer itself.

What the novel invents

In the novel, Dr. Sophie Hartmann teaches a 2187 seminar titled 'The Failure of SETI' and crosses the title out, replacing it with 'Our expectations failed.' She is a character, and Nooitgedacht University does not exist. The reasoning she uses is standard astrobiology; the 2187 census she cites is invented.

Where to read next

• — SETI Institute — educational material on search strategy and search-space coverage
• — NASA Exoplanet Exploration — transit and radial-velocity detection, transmission spectroscopy