The Quiet Galaxy

Explanations · They are there and we cannot see them

We are listening the wrong way: an efficient message is indistinguishable from noise, and they may not be using radio at all

Proposed by Michael Lachmann, Mark Newman and Cristopher Moore, 1999 fc left alone

The searches assume that a signal from another civilisation will look like a signal: a narrow tone, a regular pulse, something no natural process makes. But a message that is packed as efficiently as physics allows looks exactly like random static, and a civilisation that cared about efficiency would send that. Others may communicate with lasers, with particles that pass through planets, or with methods nobody has thought of. On this view the galaxy may be full of conversation, and our radio telescopes are tuned to a kind of signal that only a very young civilisation would ever send.

Three physicists made the sharpest version of the argument, posted in 1999 and published in 2004, starting from a result in the theory of information. The most efficient way to send a message through a channel with limited power is to use every part of the channel equally, with no pattern that could be predicted; a message encoded that way has the statistical properties of thermal noise, the same hiss that every warm object gives off. That is not a limitation of our technology but a mathematical fact: the better the encoding, the more it looks like noise. A civilisation sending information to itself across space, between colonies or probes, would use the best encoding it had, and its traffic would be indistinguishable from the natural background to anyone who did not already know the code. The authors present this as a thought experiment: they show a limit and say they have not shown how to reach it. The consequence for the searches, which look for artificial regularity, is that a message packed that well would show none.

The broader point predates the paper and has many forms. Earth's own radio leakage is falling as broadcasting moves to cables, satellites and tightly aimed beams, and the loud era of television transmitters that could be heard at a distance lasted a few decades; a civilisation a century ahead of us may emit almost nothing by accident. Deliberate messages might be sent by laser, which is harder to intercept and easier to aim, and searches for brief laser flashes are now part of the programme. Still more exotic proposals involve streams of neutrinos, particles that pass through whole planets, or patterns imposed on natural sources. A search tuned to one kind of signal is blind to the rest.

The bearing on the Drake Equation is on the last-but-one factor, the share of intelligent civilisations that are detectable, but in an unusual sense: the explanation says the civilisations are out there and transmitting, and it is our definition of "detectable" that is at fault. For the catalogue the factor is left unchanged, and the silence is put down to the design of the search.

The main objection is that the argument applies to a civilisation's private traffic, not to anything it might send on purpose to be found. A civilisation that wanted to be heard would send a signal that was obviously artificial precisely because an efficient one is not, and the searches are designed for that case. The paper does not discuss deliberate beacons. A second objection is that waste heat cannot be encoded away: whatever a civilisation does with its signals, its industry warms its surroundings, and searches for that warmth have covered about a hundred thousand galaxies, and the largest (Griffith and others, 2015) found none turning more than 85% of its starlight into heat. The reply is that those searches also rest on assumptions about what an advanced civilisation does with energy, and are themselves a bet on one kind of signal.

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: A detected signal found by a new method after decades of radio searching, showing the old methods were blind; evidence that Earth's own leakage has fallen to undetectable levels, which would confirm the loud phase is brief; a demonstration that efficient communication can also hide its waste heat.

Would weaken it: A detection by the standard radio or laser methods; evidence that advanced civilisations would have strong reasons to send recognisable beacons; surveys of waste heat around many stars and galaxies finding none, which would suggest nobody is out there to encode anything.

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 Logged, no change By hand

    No detection by any method. Toward the explanation: Garrett (2025-09-28) argues the loud phase may last decades; Garrett (2026-08-31) argues the standard infrared searches look at the wrong temperature; Vidal and others (2026-05-20) map every proposed kind of trace, including neutrinos and gravitational waves. Toward weakening it: Huang and others (2026-01) find no galaxy-scale waste heat in nearby galaxies. Optical laser searches with new spectrographs are proposed for 2026 onward, with no result yet. Logged four.

    Garrett, 2025Garrett, 2026Vidal, 2026Huang, 2026 source 1source 2source 3source 4

How seriously it is taken

The core result about efficient encoding is accepted physics and has influenced how searches are designed; as an explanation of the silence it is considered partial, since it does not account for the absence of deliberate beacons or of waste heat.

The papers that bear on it

Books, films and other work that take it up

Read next

Notes

Corrected 2026-10-16. (1) The title was given as 'why any sufficiently advanced communication is indistinguishable from noise'; the printed title ends 'technology', not 'communication' (American Journal of Physics 72(10), 1290-1293 (2004), https://pubs.aip.org/ajp/article/72/10/1290/1044411/The-physical-limits-of-communication-or-Why-any; volume and pages confirmed there and at https://arxiv.org/abs/cond-mat/9907500). (2) proposed_in was 2004, the year of the journal; the authors first posted the paper on 1999-07-30 (arXiv:cond-mat/9907500), so the year is now 1999, following the rule of first documented appearance. This is a judgment call; 2004 is the alternative. (3) The body said the authors 'accepted' that deliberate beacons would be recognisable and that overhearing is probably vain; the paper (read as the arXiv version) says nothing about beacons and calls its result a thought experiment, so those sentences were rewritten. (4) The body said waste-heat searches covered 'tens of thousands of galaxies'; the Ĝ survey covered about 100,000 galaxies and found none turning more than 85% of its starlight into mid-infrared heat (Griffith and others, Astrophysical Journal Supplement 217, 25 (2015), https://arxiv.org/abs/1504.03418).

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/listening-the-wrong-way.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.