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I know this is not really your argument, but I think it's related: I don't buy that the problem is that we just don't know what to look for. There must be some

I know this is not really your argument, but I think it's related: I don't buy that the problem is that we just don't know what to look for. There must be some observable characteristics that indicate its presence. It seems implausible that intelligent life forms would not leave any visible traces and that their planets would be indistinguishable from uninhabited ones.

Beldin 4y ago
They aren't... from nearby. Cosmic distances are vast and the telltale signs are small. I'm not sure we would have detected an abundance of sealife deep in Titan's oceans or fliers deep in Saturn's clouds. I once looked into the reach of the Arecibo message; I can't quite remember the numbers but the main point stands: it's indecipherable but detectably artificial after a short distance (guess: 60-100 lightyears), and no longer distinguishable from natural radiation after about 5× that (guess: 250ish-600 lightyears). The point is that even an intentional message quickly (in cosmic terms) becomes gibberish and, fairly soon after, too faded to even recognise as being a signal. On top of that, the receivers would have to be looking. Basically, I doubt we would recognise artificial signals intentionally sent to us from further than 15 lightyears out except with much, much luck. That explains why we didn't find any clear non-intentional signals yet. An interesting take on this is to flip the question: from how far away would we, with our current approaches, be able to unambiguously, definitively detect life on Earth? And intelligent life? I'm not sure we're able to do even the former from Pluto, let alone from the interstellar medium.
- MoSattler 4y ago
  > I'm not sure we're able to do even the former from Pluto We can communicate with Voyager 1 beyond the limits of the Solar System, so I am not sure if earth's constantly emitted signals would not be detectable from Jupiter.
  - giantrobot 4y ago
    The ability to communicate with Voyager is a function of the transmission and reception system. We have to send an incredibly focused transmission to Voyager for it to pick up our signal and listen with very sensitive instruments on a long temporal baseline to detect Voyager's signals. The inverse square law tells you that the flux of a signal decreases at a square of the distance. A receiver 2 miles away from a transmitter will receive a signal at a quarter of the strength of a receiver only a mile away. Our broadband omnidirectional broadcasts don't actually reach very far out into the solar system let alone the galaxy. Only very powerful narrowband signals reach very far and those are very directional.
nine_k 4y ago
If you were Montezuma, would you prefer to advertise your presence so that it would be visible from Spain, or would rather try to conceal your presence?
- MoSattler 4y ago
  Is earth Montezuma or Spain in that comparison?
- nradov 4y ago
  It doesn't matter, the outcome would be the same either way.

Beldin 4y ago

They aren't... from nearby. Cosmic distances are vast and the telltale signs are small. I'm not sure we would have detected an abundance of sealife deep in Titan's oceans or fliers deep in Saturn's clouds. I once looked into the reach of the Arecibo message; I can't quite remember the numbers but the main point stands: it's indecipherable but detectably artificial after a short distance (guess: 60-100 lightyears), and no longer distinguishable from natural radiation after about 5× that (guess: 250ish-600 lightyears). The point is that even an intentional message quickly (in cosmic terms) becomes gibberish and, fairly soon after, too faded to even recognise as being a signal. On top of that, the receivers would have to be looking. Basically, I doubt we would recognise artificial signals intentionally sent to us from further than 15 lightyears out except with much, much luck. That explains why we didn't find any clear non-intentional signals yet. An interesting take on this is to flip the question: from how far away would we, with our current approaches, be able to unambiguously, definitively detect life on Earth? And intelligent life? I'm not sure we're able to do even the former from Pluto, let alone from the interstellar medium.

MoSattler 4y ago
> I'm not sure we're able to do even the former from Pluto We can communicate with Voyager 1 beyond the limits of the Solar System, so I am not sure if earth's constantly emitted signals would not be detectable from Jupiter.
- giantrobot 4y ago
  The ability to communicate with Voyager is a function of the transmission and reception system. We have to send an incredibly focused transmission to Voyager for it to pick up our signal and listen with very sensitive instruments on a long temporal baseline to detect Voyager's signals. The inverse square law tells you that the flux of a signal decreases at a square of the distance. A receiver 2 miles away from a transmitter will receive a signal at a quarter of the strength of a receiver only a mile away. Our broadband omnidirectional broadcasts don't actually reach very far out into the solar system let alone the galaxy. Only very powerful narrowband signals reach very far and those are very directional.

nine_k 4y ago

If you were Montezuma, would you prefer to advertise your presence so that it would be visible from Spain, or would rather try to conceal your presence?

MoSattler 4y ago
Is earth Montezuma or Spain in that comparison?
nradov 4y ago
It doesn't matter, the outcome would be the same either way.