For decades, the search for extraterrestrial intelligence was waiting for quiet whistles from space. But our own technosphere has created a continuous radio background, like the hum of a vast metropolis. If nearby stars have sensitive antennas, they already hear this noise. SETI is now learning to pick up similar "noisy cities" on other planets.
The method has two stages: a quick sky survey for bright radio spots, then a detailed examination with a network of antennas. A technogenic source is identified by its anomalous radio brightness (it "shines" in radio like an overheated object, but without real heat), lack of circular polarization, and scintillation in cosmic irregularities. The final test is synchronous motion with the star. These observations will complement the exoplanet data from the Kepler mission William Borucki.
as written by the authors arXiv:2605.10212
The search for extraterrestrial intelligence (SETI) has traditionally focused on the detection of narrowband electromagnetic beacons. However, terrestrial technology is increasingly evolving toward distributed, low-power, wideband digital infrastructure. The strict adherence to narrowband filtering that characterises most SETI surveys, therefore, risks discarding the aggregate leakage signatures of advanced civilisations by systematically misclassifying them as unstructured noise. We investigate the feasibility of detecting such planetary-scale broadband radio technosignatures (BRaTs) using a hierarchical observational framework. In this tiered approach, wide-field radio surveys conducted by next-generation arrays (such as the SKA and its precursors) perform the initial deep-field observations, with targeted Very Long Baseline Interferometry (VLBI) providing the definitive, high-resolution follow-up. Because broadband continuum emission is largely insensitive to Doppler drift, long-duration "SETI Deep Fields" are observationally viable, extending the accessible detection volume for Kardashev Type I leakage to 100 pc. To distinguish these signals from other astrophysical confounders, a multi-parameter diagnostic framework is proposed. Candidate technosignatures are identified through a convergence of high brightness temperatures, negligible circular polarisation, spectral non-uniformity, interstellar scintillation, and sub-milliarcsecond astrometric co-motion with nearby Galactic stars/exoplanets.
If a narrow radio beacon is a lone whistle in the night, then a planet's technogenic hum resembles the cacophony of a big city: a mix of conversations, engines, and music across all frequencies.
In Carl Sagan's novel "Contact," aliens sent a complex narrow signal. The new approach suggests we're more likely to pick up the unintended noise of their technology, the same kind our own internet traffic generates.