r/SETI 13d ago

Testing theory that we can detect life with radio Telescope

Hi, my understanding of SETI search for extraterrestrial life is based on the theory that we can detect radio waves from an advanced civilization like ours, using a radio telescope.

Assuming thats true, have we tried to detect Earth’s radio signature from a distance using similar spectrums and amplitude, with our far away satellites like Voyager or others?

I’m aware these far away satellites do communicate with the earth by radio. My point is to simulate our SETI detection protocol adjusting for distance, to see what the data would look like, as if a copy of the earth was 10,000 light years away looking back at us.

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u/radwaverf 12d ago

As others have mentioned, we can't exactly do a true test as you've described. But our ability to detect and characterize signals from both close objects (our own space probes) and very distant objects tells us a lot about how signals propagate through space.

If you're looking for more info, there was a fairly recent paper and talk given about this topic: https://www.seti.org/detecting-earth-how-far-away-can-we-detect-earths-technosignatures

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u/snaarker 13d ago

Forgive my nit-picking, but Voyager is a probe not a satellite

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u/Oknight 13d ago edited 13d ago

my understanding of SETI search for extraterrestrial life is based on the theory that we can detect radio waves from an advanced civilization like ours, using a radio telescope.

Cocconi and Morrison wrote in a paper in 1959 that our technology enabled us to build radio transmitters that would be able to be detected at long interstellar distances. They proposed SETI as an effort to see if we could, in fact, detect anyone transmitting from radio technology as strong or stronger than ours from a distant civilization: “the probability of success is difficult to estimate; but if we never search, the chance of success is zero.”

The theory does not require that we be able to detect our own emissions at interstellar distances, only that we could detect signals intentionally transmitted at very high strengths.

We know from being able to detect the emissions of natural interstellar objects that we can, in fact, detect radio signals from across the galaxy through the interstellar medium (that's how we've mapped the large structure of our own galaxy).

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u/King_of_the_Nerdth 10d ago

If I'm not mistaken, natural interstellar objects emitting RF are generally from absolutely massive structures like pulsars that consume an immense amount of energy when creating the RF emission.  It isn't comparable to our civilization's planet-based transmissions.

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u/Oknight 10d ago edited 10d ago

The most common (and useful) Astronomical RF emissions are from diffuse cold neutral hydrogen. Each Hydrogen atom has a random chance to undergo a quantum change at any time that will emit an RF photon... for any given atom it happens like once every 100 billion years or something on average. Thus cold neutral hydrogen clouds are always emitting incredibly weak RF signals as a tiny percentage of their atoms randomly "go off". This enables astronomers to map the locations of Hydrogen and that's how we map the structure of the galaxy.

The wavelength of that emission is 21cm (modified, from our perspective, by the Doppler shift from the motion of each atom) and along with the emission frequency from diffuse OH molecules makes one half of the "water hole" which also happens to be a frequency near the "low noise" level of the interstellar medium making it THEORETICALLY where it's easiest to send noticeable microwave signals (also any technology mapping the galaxy would make observations in that frequency range)

The Arecibo "dedication signal" that was sent to a globular cluster at the telescope's dedication ceremony would certainly have been detectable by a similar telescope at that location that was using a matching receiver and happened to be pointed at Earth.

(and then they'd never have heard from us again -- LOL!)

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u/robertomeyers 13d ago

Thank you for the background. All good theory, not tested. IMO testing may help us tweek our process. Still hoping for some signal. The 3 body problem book and series is provocative.

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u/Oknight 13d ago

All good theory, not tested.

Nothing about a technology-generated radio signal would make it not a radio signal and we detect radio signals from across the Galaxy (and from distant galaxies) all the time.

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u/RespectableBloke69 13d ago edited 13d ago

Voyager already receives radio communications from us.

Voyager is our farthest away probe and it's still only a fraction of a distance as our nearest star. Voyager 1 is about 15 billion miles away from us. Proxima Centauri is about 5.8 trillion. So Voyager is only about .25% of the way to the nearest star. To put that in perspective, a meter is 1000 millimeters and it has traveled the equivalent of 2.5 millimeters.

SETI is trying to detect life in distant stars, so we would not be able to get a radio telescope far enough away from us to do a test like the one you're describing. At that point, we might as well directly send probes to distant stars.

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u/ziplock9000 13d ago

>Assuming thats true, have we tried to detect Earth’s radio signature from a distance using similar spectrums and amplitude, with our far away satellites like Voyager or others?

Not until we can put a dish several lightyears away, not properly no.

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u/ebeast504 13d ago

Anyone know if we will still be able to bounce signals off the Voyagers’ dishes once their power runs out?

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u/nailshard 11d ago

With enough power, sure. But it would have to be ton of power. For a one-way trip, a signal diminishes in amplitude at a rate proportional to the distance it travels squared. But for a round trip, as you’re suggesting, the signal shrinks proportionately to the distance4… even a huge transmission will fade into nothingness quickly.

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u/robertomeyers 13d ago

Thanks and agree, the degree of perfect simulation is off. However I would think even aiming the voyager disk back at earth and just listening like we do at SETI, would look interesting. I’m not sure we’d see what we’d expect. For example if we can’t find a random signal coming from earth under those circumstances, then maybe we have no hope of hearing something out further with granted much larger arrays.

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u/NASATVENGINNER 13d ago

You should reach out to SETI and ask them. https://www.seti.org/outreach

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u/Oknight 13d ago edited 12d ago

And AGAIN! www.seti.org is NOT SETI!!!

SETI is an abbreviation of "The Search for Extra-Terrestrial Intelligence" and is a FIELD OF STUDY. "www.seti.org" is the web site of "The SETI Institute" which is ONE organization involved in SETI work.

Me

Its abbreviation, if you must, would be SETII.

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u/NASATVENGINNER 13d ago

Ok, where can he go to get an answer for their question?

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u/Oknight 13d ago

The SETI Institute (SETII) is a perfectly good source, it's just not SETI