4 ms·

I always thought the more realistic answer was that the window to detect an emerging civilization is on the order of a couple decades. In that time they go from

I always thought the more realistic answer was that the window to detect an emerging civilization is on the order of a couple decades. In that time they go from simple easily detectable modulation schemes that are broadcast at very high power to modulation schemes that are nearly impossible to differentiate from noise at much higher efficiency/lower power levels. Much like we have, in the 1950's it was all high power TV/Radio signals which were radiating into space on fairly narrow bands. Now days we have really wide band signals using really advanced modulation techniques frequently sitting at or below the noise floor (GPS!) and frequently very short range (5G!). Then using your Drake equation variables calculate how many are within those couple decades at any given point that you can see.

ars 7y ago
Radar. That's the RF that's easiest to detect from long distances, it's focused, and it's strong. The hard part is deciding if it's natural or artificial.
- Beldin 7y ago
  Top of my head, so I may be off, but: The Arecibo message was easily the easiest to detect by far. Its signal will become indistinguishable from background radiation at a distance of slightly over 625 light years. The converse: any life out there trying their best to communicate with us, beyond 600 ly... we wouldn't realize it even if we happened to catch (what's left of) the signal.
  - tgflynn 7y ago
    > Its signal will become indistinguishable from background radiation at a distance of slightly over 625 light years. Doesn't that depend on how large the receiving antenna is, because the larger the antenna the smaller the source angle you can focus on and the less background radiation will be in that source angle ?
- StillBored 7y ago
  That may not last much longer either. Transponders are more effective/useful for civilian purposes and the military needs to be stealthy. Big radar installations have a sign painted on them that says "take me out first".
  - hcs 7y ago
    What about radar for asteroid detection? https://en.wikipedia.org/wiki/Radar_astronomy https://en.wikipedia.org/wiki/Radar_astronomy

ars 7y ago

Radar. That's the RF that's easiest to detect from long distances, it's focused, and it's strong. The hard part is deciding if it's natural or artificial.

Beldin 7y ago
Top of my head, so I may be off, but: The Arecibo message was easily the easiest to detect by far. Its signal will become indistinguishable from background radiation at a distance of slightly over 625 light years. The converse: any life out there trying their best to communicate with us, beyond 600 ly... we wouldn't realize it even if we happened to catch (what's left of) the signal.
- tgflynn 7y ago
  > Its signal will become indistinguishable from background radiation at a distance of slightly over 625 light years. Doesn't that depend on how large the receiving antenna is, because the larger the antenna the smaller the source angle you can focus on and the less background radiation will be in that source angle ?
StillBored 7y ago
That may not last much longer either. Transponders are more effective/useful for civilian purposes and the military needs to be stealthy. Big radar installations have a sign painted on them that says "take me out first".
- hcs 7y ago
  What about radar for asteroid detection? https://en.wikipedia.org/wiki/Radar_astronomy https://en.wikipedia.org/wiki/Radar_astronomy