Consider that our civilization has really only had about a 50 year window were we were rather noisy in the radio frequencies. Now, our radio transmissions (with the exception of some short pulse military ones) are much less powerful and would be much harder to detect at a distance.
> uoting from Tarter (2001): "At current levels of sensitivity, targeted microwave searches could detect the equivalent power of strong TV transmitters at a distance of 1 light year (within which there are no other stars)..."
We barely have the sensitivity to detect the existing strong TV transmitters of today within a 1ly sphere. The inverse square law becomes rather cruel. For a 2ly sphere, we'd need 4x the sensitivity. 3ly, 9x. To get 100 stars in the sphere, we need 21ly sphere, and that would need 400x the sensitivity that we have... and in that list of 100 nearest stars, there's only 6 G type stars.
So yes... there may be. But we're very small ( http://www.rainydaymagazine.com/RDM2011/RainyDayScience/Radi... ). Our own radio signals have barely made any significant coverage of the galaxy. Our own signals are also becoming harder to detect as our radio technology becomes better (DTV only needs 1/5th the power of analog TV).
That we're not hearing any random signals akin to what we've been broadcasting for the past century isn't surprising.
That Stack Exchange answer from 2015 is quoting a primary source describing “current levels of sensitivity” in 2001. The Breakthrough Listen initiative, launched in 2016, claims that it is sensitive to “Earth-leakage” levels of radio transmission within 5 parsecs (16 ly): https://breakthroughinitiatives.org/news/3
Radio signal is not the only way to detect presence of other civilizations.
Von Neumann style probes, Dyson spheres etc.
Current estimates place the number of planets in our galaxy at 100 billions. And some of the stars in our galaxy are ~6 billions years older than our sun, that's a hell lot of time for a civilization to develop massively considering the technological progress we have had in a just a few thousands of years.
From https://space.stackexchange.com/a/13013
> uoting from Tarter (2001): "At current levels of sensitivity, targeted microwave searches could detect the equivalent power of strong TV transmitters at a distance of 1 light year (within which there are no other stars)..."
We barely have the sensitivity to detect the existing strong TV transmitters of today within a 1ly sphere. The inverse square law becomes rather cruel. For a 2ly sphere, we'd need 4x the sensitivity. 3ly, 9x. To get 100 stars in the sphere, we need 21ly sphere, and that would need 400x the sensitivity that we have... and in that list of 100 nearest stars, there's only 6 G type stars.
So yes... there may be. But we're very small ( http://www.rainydaymagazine.com/RDM2011/RainyDayScience/Radi... ). Our own radio signals have barely made any significant coverage of the galaxy. Our own signals are also becoming harder to detect as our radio technology becomes better (DTV only needs 1/5th the power of analog TV).
That we're not hearing any random signals akin to what we've been broadcasting for the past century isn't surprising.