The Quiet Galaxy

Explanations · They are gone

Self-destruction: civilisations destroy themselves soon after they learn to build the weapons that make them detectable

Proposed by Sebastian von Hoerner, 1961 L smaller

The technology that lets a civilisation be heard across space, radio, rockets and the physics behind them, arrives in the same package as the technology that can end it. Humans learned to send radio signals into space and to build hydrogen bombs within a few years of each other. If most civilisations that reach this point destroy themselves within a few centuries, through war, engineered plagues or a machine that gets out of hand, then at any given moment almost none are left to be heard. The galaxy may have produced thousands of civilisations and have only a handful alive at once, each shouting briefly into a silence made of everyone else's ruins.

This was the first explanation anyone took seriously, because it was born alongside the question. When Frank Drake wrote his equation in 1961 to organise the first meeting on searching for signals, the factor with the widest spread of guesses was the last one: how long a civilisation stays detectable. The meeting's own educated guesses ran from a thousand to a hundred million years, and Drake's own was about ten thousand. The meeting took place at the height of the Cold War, and the physicist Philip Morrison, who had worked on the first atomic bomb, worried that societies might become detectable at about the time they gained the power to destroy themselves: he reckoned that if a typical civilisation lasted only about a decade, there would be just one in the galaxy at any time. Sagan answered that some could reach stability and last hundreds of millions or billions of years. The German astronomer Sebastian von Hoerner, writing in Science the same year, worked through the ways a technical civilisation might end, destruction of all life, destruction of higher life only, physical or mental decline, and loss of interest in science, and put the average detectable lifetime at perhaps six and a half thousand years, with the outcome dominated by how many destroyed themselves early. Carl Sagan made the idea famous: in his telling, the whole search for other civilisations was also a test of whether anyone survives what he called technological adolescence.

The argument depends on a coincidence that may not be one. The energy needed to be heard across interstellar distances, and the knowledge needed to build nuclear weapons, come from the same physics at the same stage of development. A species that can do one can do the other. Later writers added other ways out: engineered diseases, climate change driven by the same industry that powers the transmitters, nanotechnology, and artificial intelligence that replaces or discards its makers. The common thread is that the ability to destroy grows faster than the wisdom to refrain.

The bearing on the Drake Equation is entirely on the last factor, the detectable lifetime, which this view sets at centuries rather than the millions of years the optimists hoped for. Since the number of civilisations detectable at once is roughly the rate at which they appear multiplied by how long each lasts, a lifetime of a few hundred years leaves the galaxy nearly empty however often civilisations arise.

Objections: it requires almost every civilisation to fail, not most, because a single survivor with a long life would eventually dominate the count and could spread across the galaxy; humanity has had nuclear weapons for eighty years without using them again, which is weak evidence but not nothing; and a civilisation that destroys itself may leave ruins, changed atmospheres or stray probes that could still be found, so self-destruction does not entirely explain a clean silence. The reply is that eighty years is nothing, that the weapons keep getting cheaper and the failure modes more numerous, and that ruins on another planet would be far harder to see than a working transmitter.

What it says about the equation

Every explanation is a claim about one or more of the seven pieces that are multiplied to give the number of detectable civilisations. This one bears on 1 piece:

The test: what would strengthen or weaken it

Would strengthen it: Evidence of a civilisation that existed and ended, such as an atmosphere bearing the traces of industry around a star with no present signal; a demonstration that some dangerous technology is both cheap and hard to control; further close calls in humanity's own record.

Would weaken it: A detected civilisation that has been broadcasting for a very long time; a long run of human survival with nuclear and biological weapons under control; evidence that most civilisations that reach the technical stage expand off their home planet, which makes a single disaster less likely to end them.

These two lines are what the record is read against when a new paper or discovery is logged. A result of the kind named here, published with its evidence, is what would settle it; a press claim on its own settles nothing.

The last reading

Once a week the records are read against the news, each against the test above. Open a line to see what that week held. Every reading ever made of this record is on the reading page.

  • 2026-10-16 Nothing new By hand

    No paper in the window with evidence of a civilisation that ended, and no demonstration about a technology that is both cheap and hard to control. The Doomsday Clock was set to 85 seconds to midnight on 2026-01-27, the closest ever, citing the lapse of the last US-Russia arms treaty; it is a judgment, not a record, and is noted here only.

How seriously it is taken

The oldest and still one of the most widely held explanations among the public and among many scientists; its weakness, that it needs nearly everyone to fail, is well known and has pushed much of the research community toward other answers.

The papers that bear on it

Books, films and other work that take it up

Read next

Notes

Checked 2026-10-16. Von Hoerner's paper is correctly cited (Science 134 (3493), 1839-1843, 8 December 1961, https://doi.org/10.1126/science.134.3493.1839). The Science page itself could not be opened, so the paper's contents were checked through two secondary accounts that agree: https://en.wikipedia.org/wiki/Sebastian_von_Hoerner (four causes of an end: wiping out all life, killing only the intelligent species, decline in mind or body, loss of interest in science; average duration 6,500 years) and https://www.universetoday.com/articles/beyond-fermis-paradox-ix-what-is-the-brief-window-hypothesis (6,500 years). "Technological adolescence" is Sagan's phrase: Discover magazine quotes his 1978 Smithsonian piece, "A single message from space will show that it is possible to live through technological adolescence" (https://discovermagazine.com/the-sciences/how-advanced-are-we-earthlings-heres-a-cosmic-yardstick). Corrected 2026-10-16: the body said several people at the 1961 Green Bank meeting thought the lifetime might be a few decades, and that this factor worried everyone in the room. No source supports "several". The meeting's guesses for the lifetime ran from 1,000 to 100,000,000 years (summarised at https://en.wikipedia.org/wiki/Drake_equation; Drake's own account was not reached). The one documented short estimate is Philip Morrison's, about a decade, with Sagan's reply and Drake's own guess of 10,000 years, in Lee Billings's account (https://slate.com/technology/2013/09/green-bank-conference-seti-frank-drakes-equation-for-estimating-the-extraterrestrial-life.html, adapted from his book Five Billion Years of Solitude); that account also ties the "technological adolescence" worry to Morrison at the meeting. The body now says this. No change to the id, family, bears_on or the would_strengthen and would_weaken lines.

Think this page gets the explanation wrong, or misses an objection? Say so, or read how disagreement gets folded in. The record itself is data/explanations/self-destruction.toml in the public repository. This page's address will never change; if the explanation is ever retired, the address will say what replaced it.