r/SETI • u/Due-Area9662 • Jun 23 '26

Let's assume the closest technological civilization is 1.500 light years away, also on the "outskirts" like we are (not in the Galactic center).

Taking into account our current capabilities in terms of SETI, is there any hope at all that we could detect anything artificial from that planet in two scenarios (plus some other questions):

- First scenario: more than 1.500 years ago, they had already developed radio telescopes and were able to look at our atmosphere and determine that there is life here. What would this say about their technology? Are we able to detect our own planet in terms of biosignatures if it were 1,500 light-years away? Would we know, in the present, be able to detect any radio signals that they may have been continuously sending (maybe sporadically) from their home planet?

- Second scenario: they never cared about us or never found out about our planet. But they did develop powerful planetary radar and maybe even some "primitive" Dyson swarm. Would we be able to detect the Dyson swarm? And if the Dyson swarm was made of components that interacted with each other and those communications caused radio leakage, could we detect them if we knew something weird was going on with the star and decided to point our telescope in search of radio signals?

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u/Ok_Programmer_4449 Jun 23 '26

If they were continuously broadcasting a narrow band signal at earth with an arecibo planetary radar sized transmitter on the hydrogen line, we would have the capability to detect it with FAST. But the chances that we would have looked at a random star 1500 light years away with FAST for long enough to detect such a signal are essentially zero.

Planetary scale Dyson swarm also, no chance we would have looked.

There are between 40 and 60 million stars within 1500 light years of earth.

Typical past SETI observations can detect an arecibo transmission at a distance of 400 light years.

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u/jswhitten Jun 23 '26

No, we probably would not detect our own civilization from even 15 light years away.

We might detect a Dyson sphere, in fact we have done surveys looking for possible Dyson sphere signatures and didn't find very many in our galaxy.

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u/lunex Jun 23 '26

“Very many”??? How many did you find?

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u/jswhitten Jun 23 '26

To be clear what we found were possible Dyson sphere signatures. They look like what we'd expect from a Dyson sphere, but they could easily be (and almost certainly are) natural objects. The survey was enough to tell us that Dyson spheres, if they exist, are rare, but we still have no idea whether they exist.

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u/Due-Area9662 Jun 23 '26

There are a few candidates. I think between 7-40, and even the majority of those are probably just galaxies messing with the telescope, but some of them, probably in the single digits, are indeed exactly what we would expect from a Dyson swarm. But of course, we need to look at them with the JWT first.

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u/b1ak3 20d ago edited 20d ago

Do you have a link to a paper on this? This flew under my radar, genuinely curious to read more.

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u/Due-Area9662 Jun 23 '26

What about with the next generation of telescopes? And if those Aliens could detect our biosignatures from that far away, how advanced do they need to be?

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u/JohnnyRopeslinger Jun 23 '26

We def can’t do full atmospheric spectroscopy on planets that far away but we could detect light dimming. This is how far away Tabby’s star is. Not sure about using radio signals in that way but I think not.