Eavesdropping on Radio Broadcasts from Galactic Civilizations with Upcoming Observatories for Redshifted 21cm Radiation · HackerPapers discussions

Eavesdropping on Radio Broadcasts from Galactic Civilizations with Upcoming Observatories for Redshifted 21cm Radiation — mentioned by MontyCarloHall

Wed, 21 Jan 2026 13:08:57 GMT

>Even humanity’s (weak) radio emissions would be detectable from tens of light years away, and stronger emissions from much further. That's not true. Non-directional radio transmissions (e.g. TV, broadcast radio) would not be distinguishable from cosmic background radiation at more than a light year or two away [0]. Highly directional radio emissions (e.g. Arecibo message) an order of magnitude more powerful than the strongest transmitters on Earth would only be visible at approximately 1000 light years away [1], and would only be perceptible if the detector were perfectly aligned with the…

Paper and discussion history. A mention is not an endorsement.

Eavesdropping on Radio Broadcasts from Galactic Civilizations with Upcoming Observatories for Redshifted 21cm Radiation — mentioned by MontyCarloHall

Tue, 20 Dec 2022 15:06:42 GMT

I post this on every Fermi paradox thread. Non-directional radio transmissions (e.g. TV, broadcast radio) would not be distinguishable from cosmic background radiation at more than a light year or two away [0]. Highly directional radio emissions (e.g. Arecibo message) an order of magnitude more powerful than the strongest transmitters on Earth would only be visible at approximately 100 light years away [1], and would only be perceptible if the detector were perfectly aligned with the transmission at the exact time it arrived. Space is really big, and radio emissions are comparatively really…

Paper and discussion history. A mention is not an endorsement.

Eavesdropping on Radio Broadcasts from Galactic Civilizations with Upcoming Observatories for Redshifted 21cm Radiation — mentioned by MontyCarloHall

Sat, 26 Nov 2022 16:27:35 GMT

While they may not be perfectly isotropic, they are far from being directional (most TV transmitters are monopoles with uniform azimuthal radiation) and would still not be distinguishable from background radiation (regardless of its distribution) at more than a light year or two away [0]. Highly directional radio emissions an order of magnitude more powerful than the strongest transmitters on Earth would only be visible at approximately 100 light years away [1]. [0] https://physics.stackexchange.com/a/245562 [1] https://arxiv.org/pdf/astro-ph/0610377.pdf

Paper and discussion history. A mention is not an endorsement.

Eavesdropping on Radio Broadcasts from Galactic Civilizations with Upcoming Observatories for Redshifted 21cm Radiation — mentioned by MontyCarloHall

Mon, 31 Oct 2022 11:16:30 GMT

Space is really big, and radio emissions are really weak. The strongest isotropic radio emissions from Earth (e.g. high power TV broadcasts) would be indistinguishable from background radiation at only a light year or two away. One study [0] suggests that directed radio emissions an order of magnitude more powerful than the most powerful radio emitters on Earth could be detectable at ~100 light years (1/1000 the diameter of the Milky Way), but our detector would have to be perfectly aligned with the transmission at the exact time it reaches Earth. [0] https://arxiv.org/pdf/astro-ph/0610377.pdf

Paper and discussion history. A mention is not an endorsement.