How Sensitive Must SETI Arrays Be to Detect Extraterrestrial Signals?

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Discussion Overview

The discussion revolves around the sensitivity required for SETI (Search for Extraterrestrial Intelligence) arrays to detect signals from extraterrestrial civilizations. Participants explore the relationship between the strength of potential signals emitted by advanced extraterrestrial technologies and the sensitivity of current detection systems. The conversation touches on theoretical aspects of signal transmission, detection capabilities, and the implications of signal directionality.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Fermi's question about the lack of communication from extraterrestrial civilizations raises the issue of whether the sensitivity of SETI arrays or the strength of extraterrestrial signals is the limiting factor.
  • Some participants suggest that the loudness of a signal required to be detected from distant parts of the galaxy depends on how directional and focused the signal is.
  • One participant mentions the potential for searching for laser-borne signals and discusses the use of gravitational lensing to enhance signal detection.
  • Another point raised is that current SETI efforts may be more focused on detecting radar signals rather than traditional radio signals, which could influence the design and power of the signals being sent.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of detecting signals from distant stars, with some emphasizing the need for highly focused beams while others suggest that only nearby stars may be viable targets. The discussion remains unresolved regarding the optimal conditions for signal detection and the necessary characteristics of extraterrestrial transmissions.

Contextual Notes

Participants note that the effectiveness of signal detection is contingent upon various factors, including the directionality of the signal and the specific technologies employed in SETI searches. There is acknowledgment of the complexities involved in both transmitting and receiving signals across vast distances.

Canada Bob
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TL;DR
SETI
Fermi asks "why don't we hear from them" could that be because they don't "shout" loud enough or maybe our ears are sensitive enough to pick up a signal emitted by advanced ET's within just our own backyard.

Is it down to the sensitivity of the SETI arrays, or the strength of a signal from within our own galaxy to be picked up by the SETI or any other array on Earth ?

How "loud" would a signal have to be to travel from the further reaches of our own galaxy to be picked up by SETI, how much power would that transmission need ? is it possible to transmit such a powerful signal ?

Yea, I know, it's 6 of one and half a dozen of the other, hopefully there's an overlap as to how strong a signal could be and how sensitive a receiver could be ?

Bob.
 
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Canada Bob said:
Summary:: SETI

How "loud" would a signal have to be to travel from the further reaches of our own galaxy to be picked up by SETI, how much power would that transmission need ? is it possible to transmit such a powerful signal ?
That's not answerable without knowing how directional and focused the signal is. Think of an old fashioned lighthouse with only a flame as a light source. Ships 20 or more miles out to sea can see the flash of light.

But even with a highly focused beam, I think the only chance is from nearby stars.
 
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IIRC, this is why there's now efforts to search for laser-borne signals.

One 'gotcha' on collimation etc is to use system star as Einsteinian lens.
IIRC, our 'focus' at ~550 AU, ~3 light-days, would give 'a few metres' resolution imaging of stars and planets out to 50-some light-years, 'kilometres' to thrice that.

Snag is each target system would probably need its own observatory and out-riders.

Conversely, the same 'lensing' could be used to practicably transmit towards those systems without requiring 'absurd' beam energies...

Down-side is improbability of intercepting such unless aimed our way...

Could be said that getting out to 'focus' represents a major 'filter'...
 
According to Seth Shostak, SETI searches aren't really looking for radio: they are looking for radar, presumably as part of a meteor early warning system. There is incentive to make the beam as powerful as you can and as directional as you can ( @anorlunda's point).
 

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