Observational Signatures of Self-Destructive Civilisations

TL;DR

This paper explores how signs of self-destruction in intelligent civilizations could be observed astronomically, impacting our understanding of Fermi's Paradox and guiding future detection efforts.

Contribution

It introduces scenarios of self-destruction with observable signatures and discusses their implications for SETI and the Drake Equation.

Findings

Certain atmospheric signatures could be detectable with next-generation telescopes.

Timing of observations is critical due to rapid decay of some signatures.

Some signatures may persist long enough for serendipitous detection.

Abstract

We address the possibility that intelligent civilisations that destroy themselves could present signatures observable by humanity. Placing limits on the number of self-destroyed civilisations in the Milky Way has strong implications for the final three terms in Drake's Equation, and would allow us to identify which classes of solution to Fermi's Paradox fit with the evidence (or lack thereof). Using the Earth as an example, we consider a variety of scenarios in which humans could extinguish their own technological civilisation. Each scenario presents some form of observable signature that could be probed by astronomical campaigns to detect and characterise extrasolar planetary systems. Some observables are unlikely to be detected at interstellar distances, but some scenarios are likely to produce significant changes in atmospheric composition that could be detected serendipitously with next-generation telescopes. In some cases, the timing of the observation would prove crucial to detection, as the decay of signatures is rapid compared to humanity's communication lifetime. In others, the signatures persist on far longer timescales.