Summary · Dxtra Inc. (dxtra.com)
We look at communication with galactic reach from the system designer’s point of view. A network meant to outlive its builders spends almost no energy: it builds no transmitters, modulates sources that already radiate, and gates its message on the receiver’s capability. Twenty-nine searches of public solar and heliospheric archives tested that hypothesis — twenty-five null, three void, one recovering a known signal as the positive control. This was not hand-waving: together the searches came to roughly a hundred million individual statistical tests — about 1015 floating-point operations, some eighty days of a 1976 Cray-1 running without pause — and that is only the shallow end of a combination space whose full depth runs to Cray-1 years, as the compute table below sets out.
▶ Watch first: The Patient Network Half a billion years in six animated minutes — the whole idea, start to finish. Then come back here for how we actually searched.SETI as practiced since 1960 is a listening watch: point a large dish at a star and scan for a narrowband carrier near the 21 cm hydrogen line — 1420 MHz, the quietest stretch of the microwave window and the natural calling frequency any radio-literate civilization could find. Project Ozma did it in 1960 with an 85-foot dish and a single channel. SETI@home spent two decades farming data from the 1000-foot Arecibo dish out to millions of volunteer PCs — for a while the largest computation on Earth, and many readers of this page will have run it. Breakthrough Listen does it today with billions of channels across 1–10 GHz. Every generation has brought bigger dishes, lower noise figures and finer bin widths, and sixty-five years of steadily better receivers have returned one thing: silence. No confirmed carrier, no repeating pulse — one unrepeated 72-second anomaly in 1977, and nothing since. The silence may even be partly self-inflicted: a 2026 study (Gajjar & Brown, ApJ 999) finds that turbulence in the host star’s own wind smears a narrowband carrier into broad Lorentzian wings before it ever leaves the system — at 1 GHz, roughly 70% of stars broaden a line past 1 Hz, and a CME encounter smears it by thousands — while the standard pipelines are matched filters for an infinitely sharp line. Power spread into the wings is sensitivity silently lost.
And it is worth flipping the question: how far could our signals be heard, by receivers no better than our own? A 2025 SETI Institute study (Sheikh et al., “Earth Detecting Earth”) ran the numbers with Earth-2024 technology on both ends of the link: our planetary radar — Arecibo at 20 TW EIRP — would stand out at 12,000 light-years; the Deep Space Network at 65; and the combined mobile-phone leakage of the entire planet at just 4. The loudest thing humanity has ever put on the air was pinging asteroids. Everything we broadcast to each other barely leaves the neighborhood.
Any ham knows the feeling, and knows what it usually means. A band that sounds dead on a carrier scan can be carrying dozens of QSOs at 20 dB below the noise floor; you hear nothing because you are listening for the wrong mode, not because nobody is on the air. Our claim is that the silence is a design feature. A sender engineering for deep time would never keep a megawatt carrier keyed for a million years on the chance that somebody tunes by — and a message meant only for capable receivers is deliberately not hearable on a bare carrier scan. If that is the design, the place to listen is not a quiet frequency. It is the behavior of sources already on the air. That is what the rest of this page is about.
Design the system before you search for it. A communication network with galactic reach outlives its builders by millions of years. It has to run with no maintenance, and it has to be parsimonious with energy above everything else. Take those constraints seriously and three design decisions follow.
1. Build no transmitter. Stars already radiate more power than any machine ever could. The cheap way to signal is to modulate emission that already exists — redistribute a star’s own flux in a recognizable pattern — rather than generate a single watt of new signal.
2. Write in ratios. A sender who shares no clocks, no meters and no units with the receiver can only use dimensionless quantities: relationships among measurements. The message is not on any one channel. It is in how observables move together.
3. Spend nothing on receivers who cannot act. Gate the message behind a proof of capability — cheap to set, trivial to verify, solvable only by a receiver advanced enough to do something with the contents.
The behavioral SETI hypothesis is that such a network is already in place: passive, long-lived, carried on natural sources, gated on capability. That changes what a search looks like. Sensitivity is not the limit — knowing which combination of measurements to examine is. Rules 2 and 3 make that problem finite: a combination space that can be enumerated, searched, and — unlike a channel — have its coverage measured.
Every category in the field’s reference taxonomy — the 2018 NASA Technosignatures Workshop — assumes something built: a transmitter, a structure, a byproduct, an artifact. This search assumes none of them.
| Category | Assumes | Here |
|---|---|---|
| radio — narrowband or pulsed | a dedicated transmitter, powered and pointed | not assumed |
| optical / infrared — laser pulses, beacons | a dedicated transmitter, at higher power | not assumed |
| megastructures, waste heat | a structure large enough to occult or re-radiate a detectable fraction of the star | not assumed; the modulator is ~10−6 of the disc and invisible as an occulter |
| atmospheric — industrial species | an industrial byproduct | not assumed; nothing here is a byproduct |
| solar-system artifacts | a physical object to image or encounter | not the carrier here |
| planetary surface — city lights | a modified planet | not assumed |
Three differences follow. The carrier is a relationship among observables rather than a channel to point at. The gate is opened by the receiver's capability rather than paid for by the sender. And the target is our own star, from archives already collected — where the workshop's emphasis is on new instruments and on piggybacking planned missions. That premise does not appear in the workshop's taxonomy, and the archives it points at — solar and heliospheric records collected for space weather — do not appear in its inventory of what has been searched.
And not the dark forest. A frequent reflex is to file this under Liu Cixin’s dark forest — the idea that the sky is silent because every civilization hides and destroys anyone who signals. It is the opposite claim. The dark forest explains silence through fear and predicts nothing to find; this predicts an efficient, capability-gated network and says exactly where to look for it. One is an argument for not searching; the other is a search. The overlap — neither expects a loud beacon — is a premise shared by most serious SETI thinking, and is not by itself the dark forest.
The framework is not a claim about what a sender wants. It is an engineering derivation: what would a communications designer, facing an unknown number of unknown recipients over geological time, be forced to build? Four constraints — energy, parsimony, longevity, gating — each delete something, and what survives is a chain.
| Step | Gate it passes | |
|---|---|---|
| 0 | The decision, under a budget — total energy across all recipients and all time is minimized | — |
| 1 | Galactic survey — candidates identified remotely, before anything is spent on them | stellar filter — ~109 candidates from ~1011 stars |
| 2 | Mesh deployment — a passive listening network seeded first, from a carrier bus | the address exists |
| 3 | Probe launch — automated, self-repairing, transit 104–106 yr, unsupervised | survival in transit |
| 4 | Emplacement at the star — high in the stellar atmosphere, where the cheap channels form | persistence — the framework's largest unsupported assumption |
| 5 | The signal is embedded — a small dimensionless modulation carrying a pointer to one mesh node, repeating indefinitely | the puzzle is posed |
| 6 | Maturity — continuous monitoring, long archives, compute to search a combination space, all arising for the receiver's own reasons | capability |
| 7 | Recognition — realizing that a puzzle has been posed at all. Costs nothing, and that is the difficulty | gate 0 — invisible from below. The hardest gate in the chain |
| 8 | Detection — right channel, right cadence, right combination | coverage of the combination space |
| 9 | Decode — the encoding inverted without shared units | proof of work — the decode is the demonstration |
| 10 | The pointer is acted on — the receiver's first real expense: it must build a transmitter | the gate opens — that expense is the filter |
| 11 | The mesh receives the reply — at the named node, listening at zero idle cost | — |
| 12 | The return — a response service acting for the sender, answering on parallel narrow beams | — |
The architecture is designed to outlive its designer, and that is a core principle rather than a flourish. The longevity constraint is one-sided: it binds below, at the emergence of a receiver, and sets no upper bound — nothing in the architecture specifies a date at which the mesh stops, and no element of it is given a design life.
That is forced by the chain's own numbers. A bus crosses a 104 ly route in 7×104 yr; probes transit unsupervised for 104–106 yr; and the receiver takes 106–109 yr to arise. A designer who requires their own survival anywhere in that span has built a system that fails on the most probable branch. A Drake-style estimate multiplies by L, the civilization's lifetime; if the artifact outlives its designer, L is the wrong lifetime to multiply by. "Is anyone alive out there" and "is anything out there still running" come apart, and this searches for the second.
If the message is conditional on solving a problem, the first barrier is not solving it but recognizing that a problem has been posed. That barrier is invisible from below: a civilization holding the right archives, at the right cadence, sees exactly what a civilization with no signal to find sees. The recognition gate has a size, and the size is set by the carrier — a message carried in a relationship among observables is findable only by a receiver able to search relationships, which is a compute threshold, not a telescope.
| Search tier | FLOP | Cray-1, 1976 | 88 cores | Frontier |
|---|---|---|---|---|
| triple sweep | 5.5×1014 | 39.8 d | 52 min | 0.4 ms |
| quadruple sweep + matched null | 2.9×1014 | 21.0 d | 27.5 min | 0.2 ms |
| every search in this paper | 1.1×1015 | 79.6 d | 1.7 h | 0.8 ms |
| T3 — quadruples over 30 channels | 2.7×1017 | 53.5 yr | 17.8 d | 0.2 s |
| T6 — quadruples over 60, fast band | 2.8×1023 | 5.5×107 yr | 50,409 yr | 57.5 h |
Our own position on that ladder is measurable rather than rhetorical. The pair space of thirty observables closes in under an hour on one machine; the triple space took 117 million statistic evaluations and 26 hours. The recognition gate weakens a common premise of the Fermi paradox — that contact would be self-announcing — without requiring absence, concealment or a great filter.
The correspondence is exact, and naming it is what makes the search design falsifiable rather than a matter of taste. The gate is a symmetric cipher under brute-force key search, and this paper runs the cryptanalyst's side of it.
| Cryptographic object | Here |
|---|---|
| the key | the tuple (which observables, which functional form) |
| the ciphertext | the public archive — already collected, by someone else, for other reasons |
| the plaintext | the imposed modulation |
| the key space | C(N,k) × |F| — enumerable, which is why coverage is a number |
| exhaustive key search | the sweep of §4: every admissible key tried, the statistic as the oracle |
| unicity distance | the multiple-testing threshold — below it, more than one key yields a plausible decryption |
What makes the scheme work at all is self-identifying plaintext. A receiver knows when the right key has been tried because the statistic fires — no crib and no known-plaintext pair is needed. That is the same property that makes brute-force search viable, and it is why the sender need not transmit anything to tell you that you have succeeded.
Two consequences of taking the analogy seriously. It satisfies Kerckhoffs's principle in its purest available form: nothing is hidden, the whole scheme can be published, and the security lies entirely in the work. And it is not proof of work in the hashcash sense — there the sender performs the work to price a message; here the receiver performs it, and the direction of payment is inverted. The nearest technical antecedent is not in the SETI literature at all but in Rivest, Shamir & Wagner's time-lock puzzles (1996), which set difficulty from projected future hardware speed. One difference is favourable here: a time-lock puzzle is inherently sequential and its delay cannot be bought off with more machines, whereas a key search parallelizes — which is precisely why the compute table above is a table of wall-clock times rather than of impossibilities.
The deepest verified limit is 1.4×10−6 in fractional Lyman-α irradiance at two minutes, at 95% recovery. Two channels were searched here for the first time: SOHO/VIRGO SPM photometry at one minute over 27.3 yr, and SOHO/GOLF Doppler velocity at 20 s over 25.9 yr.
The same instrument, days and pipeline are 245× more sensitive at two minutes than at one day. The binding constraint is not how faint a signal can be seen — it is how much of the combination space has been looked at.
| Coverage | Result |
|---|---|
| Pair space, after acquiring 17 further observables | 18% → 88% — 382 of 435 pairs |
| Tests spanning the Sun–heliosphere boundary | no survivor in 510 |
| Triples, of 4,060 (2,934 reachable) | 2,749 completed → void |
| Cross-viewpoint, Earth line against Mars line | null to 8.9×10−4 at 3 d |
| Reason | n | A statement about |
|---|---|---|
| nothing above threshold | 22 | the sky. The detector worked, the control passed, the channel was empty at the stated level |
| underpowered | 3 | the analysis — could not have found the effect if present |
| detector failed its own control | 1 | the analysis |
| no defensible null | 1 | the analysis — "no signal" cannot be specified for a star with its own higher-order structure |
| the Sun is too loud | 1 | the data. Not repairable by analysis |
| detection | 1 | a known signal, recovered as a positive control |
Solar p-modes in GOES EXIS Mg II irradiance, comb spacing 135.1 and 135.0 µHz on the two spacecraft against an accepted 134.9. Priority belongs to Eden et al. (2024), and we claim none. Its value here is as a positive control whose answer was fixed in advance and corroborated by an independent group — a stronger check on the pipeline than any self-designed injection.
A null result bounds an amplitude; it does not settle existence. What the limits establish is that no dimensionless modulation exceeding the stated amplitude exists in the stated observable over the stated band, during the interval observed — and every qualifier there is load-bearing.
The framework of the opening sections is not claimed to be supported by these results, and is not invoked to explain them. What is new is narrower than the machinery around it: that the carrier may be a relationship among observables rather than a channel to point at, that the resulting space can be enumerated and its coverage measured, and that a capability-gated sender needs nobody to abstain from anything.
Four things block the next tier, and only one of them is compute. They are listed in the order that matters, which is not the order of cost.
The triple space returned void, and the quadruple space would too, for the same reason: there is no defensible null for higher-order statistics of solar output. The question, stated without reference to technosignatures, is this: what is the null distribution of bispectra, trispectra and cross-channel phase alignment of solar output? Nobody knows.
Observation cannot answer it. We have one Sun and one realisation of it; a null distribution requires an ensemble, and the only ensemble available is a synthetic one.
The project. A large ensemble of independent global solar convective-dynamo simulations — Rayleigh, ASH or MURaM class — each integrated over several simulated activity cycles, from which synthetic disc-integrated irradiance and velocity series are drawn and the higher-order statistics measured across members.
Scale. At literature cost of 5×105 to 2×106 core-hours per realisation, an ensemble of 50–200 members is 0.4 to 1.8 million node-hours — within a single INCITE-class award, and modest by the standards of the simulations themselves.
What it unlocks. The triple and quadruple spaces become searchable, the void results become limits, and any future search for non-linear coupling in solar data inherits a characterised false-alarm rate. The value is not specific to SETI.
The gate this project must pass, stated first because it decides whether it is worth running. A null built from simulations that do not reproduce the Sun in the statistics being tested is worse than no null: it would license exactly the false positives the discipline of this paper exists to prevent. The ensemble has to be validated against the real Sun in the same statistics before any limit derived from it means anything.
The tiers are not blocked on machines — T3 is 17.8 days on the single workstation used here, and 0.2 s on Frontier. This table should not be read as asking for a machine. It is here to show that the compute is not the binding constraint, which is itself the finding.
| Tier | Scale | What it would buy |
|---|---|---|
| T3 — quadruples over 30 channels | 27,405 keys × 4 forms ~18 d on one 88-core machine | nothing, until a defensible four-body null exists |
| T6 — quadruples over 60 channels, fast band | 2.8×1023 FLOP 6.2 d on a dedicated exascale machine | the same objection, more strongly |
| Peak-bagging, full Lorentzian profile fits, GOLF | days, not hours | row 7 sits at 1.46×10−5 against a designer level of 10−6; a ten-candidate estimator search bought 1.33× |
| N2 surrogate counts in place of the tail fit | the reason the fit was introduced | the generalised-Pareto extrapolation is unstable across realisations at 1.7% of triples |
Before any instrument is built, two datasets that already exist would open the two best-motivated channels in the programme — both blocked, when this summary was first written, by release policy rather than physics. The remedy, we wrote, is a letter, not a telescope. For one of the two, the letter has now been sent, answered, and acted on; the other remains blocked.
The Super-Kamiokande solar-neutrino time series — OPENED, September 2026. The neutrino channel is the only direct, unmediated probe of the solar core — photons random-walk out over ~105 years; neutrinos leave at once. The pointed gap stood: every published analysis of that data was a periodicity search, and the aperiodic question — structure keyed to the receiver’s situation rather than to a clock — had never been asked, by anyone. A data request sent to the collaboration on 16 September 2026 was answered by its spokesperson the next day, with a pointer to a public 5-day-binned series over the full 5,804 live days (1996–2018) and a commitment to re-link the older tables our letter had reported missing. Per-event data stays collaboration-only, for a stated physics reason: the background rate is not time-stable.
The aperiodic question has now been asked — of that series, of Borexino’s open-data 8-hour 7Be rate (2011–2021), and of the two detectors jointly over their 2011–2018 overlap. All three searches are null, with every control passing: no aperiodic structure above 4.5–6% (Super-K, 10 d – 22 yr), above 8–12% (Borexino, 16 h – 100 d — the first limits of any kind in that band), or above ~4.5% coherently in both detectors, where no instrumental effect can follow. The 1–3% window the beacon physics allows remains open, and now waits on data that does not yet exist publicly — Super-K past 2018, or the JUNO / Hyper-Kamiokande era. Methods, injection curves and provenance: the paper’s September 2026 addendum.
And that era has a date. Hyper-Kamiokande — 260,000 tons of water, a fiducial volume ten times Super-K’s, operations from 2028 — will log ~150 solar-neutrino events a day where Super-K logs ~15. The physics is on the sender’s side here: ⁸B neutrino production scales as roughly the 25th power of core temperature, so the star is its own amplifier — a temperature nudge of 4 parts in 10,000 in the core is a 1% flux change at the detector, delivered in 8.3 minutes with nothing in the path to smear it. Run the same search battery on Hyper-K’s first decade and the reach improves from 4.5% to about 2%; two decades brings ~1.5% — inside the 1–3% window the amplifier physics allows, for the first time. In receiver terms: if the deepest register is in use, the nulls so far bound only the loud versions, and we are at the beginning of the detection threshold, not past it. The gate opens on detector mass now being poured.
Multi-epoch pulse profiles. The magnetosphere channel ranks at K = 1.53, higher than most of what was actually searched, and the test is fully designed — only the archive is missing. The public TPA cut is single-epoch (Nsub: 1); CHIME/Pulsar reduces its 250 TB/yr on site and releases products, not epochs; the EPTA and NANOGrav releases are timing files with the profiles marginalised away; and the EPN database’s best-covered pulsars appear in three references that are different papers at different frequencies. Assembling a per-pulsar, per-epoch profile archive is a curation project on data that has already been taken.
Why these two outranked the ensemble and the exascale rows above — and what the test of that claim returned. Both channels carry a designed, physics-anchored test waiting on nothing but access, and the cost is a data request. This section originally closed: if this programme reopens, the first action is an email to the Super-K collaboration — not a new statistic, and not a machine. That email was sent, answered within a day, and the channel went from blocked to measured inside forty-eight hours — the cheapest item on this page, and the only one so far to convert. The remedy really was a letter. One channel remains blocked: the per-pulsar, per-epoch profile archive — a curation project on data that has already been taken, still waiting on nobody in particular.
Four columns are blank across the whole seventy-year record, and no amount of compute or patience fills them:
Every long solar series is a concatenation across instrument handovers, and a slow signal spanning one could be destroyed by cross-calibration or manufactured by it. One of the 29 searches is spent as a control on exactly that: GOES-15 against GOES-16 X-ray over 1,031 dual days, which measured a 27.7σ shift in detector output across the handover while the search result itself did not move.
This is the binding constraint, and it is the one the paper cannot lift. Whether we happen to measure the particular combination a sender chose is roughly one chance in five for a pair and one in eleven for a triple, and it cannot be improved by better instruments on the channels we already have. Only by measuring more things.
And one instrument just arrived. The Nancy Grace Roman Space Telescope launched on 30 August 2026; its Galactic Bulge Time-Domain Survey will deliver time-series photometry of order 108 stars at a ~12-minute cadence — six 72-day seasons over five years, under Roman’s mission-wide policy of no proprietary period: every image public on arrival. The single-channel searches in this programme run on a stellar light curve unchanged. Roman is the first archive on which the behavioral question can be asked of a hundred million stars at once, rather than of one.
Behavioral SETI is offered here as a hypothesis, not as a result. Its claim is narrow: that a sender constrained by energy, parsimony and longevity would encode not on a channel but in a relationship among observables, and would gate the message on the receiver's demonstrated capability rather than pay to make it legible. Everything in the search above is downstream of that, and none of the twenty-five nulls is evidence for it.
Where it touches the Fermi paradox is at a single premise. The paradox is usually posed as a contradiction between expectation and silence — they should be here, or we should have heard — and it inherits, mostly without argument, the assumption that contact would be self-announcing. A capability-gated signal is not. It is invisible from below by construction: a civilization holding the right archives, at the right cadence, that has not yet thought to search relationships sees exactly what a civilization with nothing to find sees. That weakens the premise without requiring absence, concealment, or a great filter — which is the whole of the contribution, and it is a smaller thing than it may sound.
The nearest hypothesis in the literature is Ball's zoo hypothesis (1973), and the relationship is worth stating precisely, because the two share a prediction and share no mechanism at all.
| Zoo hypothesis (Ball 1973) | Capability gating | |
|---|---|---|
| Predicts | silence despite presence | silence despite presence |
| Requires | coordination — many civilizations abstaining, indefinitely | nobody to abstain at all |
| Fails when | a single defector breaks it | it does not have this failure mode: the barrier is difficulty, not etiquette |
| Enforcement | external, and must be maintained | self-enforcing — opened by the receiver's own capability |
It is not a third position in the same debate. The three are different kinds of object. The Fermi paradox is an observation that demands an explanation. The zoo hypothesis is an explanation that forbids no observation — as stated, nothing can contradict it. Behavioral SETI is an explanation that makes quantitative predictions: which channels, at which amplitudes, behind which gate. That is its entire claim to attention, and it is a claim neither of the others can make.
A confirmed gate would collapse both. If the chain of §2 were verified on any channel, the paradox would dissolve — the sky looked empty because the signal is conditional, not because no one is there — and the zoo hypothesis would fail as stated, since a conditional invitation is not deliberate non-contact. The framework can be shown to be right, and being shown right would settle both questions. It has not been shown right here.
What the searches returned is twenty-five nulls at stated sensitivities. They are bounded statements about particular observables at particular amplitudes, and they are not offered as support for the framework that generated them. The framework is credited with producing the searches, not with surviving them. Two further consequences are drawn: it weakens the self-announcing premise without requiring absence, concealment or a great filter, and it argues that a search of this kind should report coverage rather than detections, coverage being the only quantity that accumulates.
One move is refused. A null must never be read as the gate was simply not open to us. That reading would absorb any non-detection and would turn this into the zoo hypothesis with arithmetic attached. The tests decide the outcome; the framework does not get to explain the outcome away.