[WillPostForFood]

is absurdly premature.

Only relative to our own existence. If the universe is ~14 billion years old, and life was plentiful, you might expect life to have emerged elsewhere hundreds of millions or a few billion years before us. That allows for enough time for signals to have reached earth, even at slow light speeds.

[omnicognate]

That part was more about us being detected by others, really. The portion of the galaxy within which aliens could theoretically have noticed us since we developed radio technology and responded in a way we could have noticed by now is tiny.

As far as us noticing other civilisations is concerned the second point is the major one: the signals involved would just be really, really tiny. The "prematureness" is relative to our development of technology that could detect them.

You can of course posit that really advanced civilisations would produce massive energy signatures but I'm not sure that makes sense. The visible night time glow our planet produces due to our presence is a signature of inefficiency and light pollution. I'd hope that with better technology and politics we could make our planet look dark again from space. Efficiency, lack of wasted energy seems at least as likely to be a hallmark of a very advanced civilisation as huge, catastrophic energy releases. And even if those energy releases exist and really are spectacularly huge they'd still be massively hard to spot.

[WillPostForFood]

It is plausible that our visible light signature might be reduced (though I don't agree it is necessarily wasteful - like lighting up evening outdoor events). But we should consider the entire RF spectrum. You'd have to go to an extreme to not have a modern civilization without notable RF emissions at some level. (e.g. Dyson sphere).

Section 2 of this paper has some fun info on the ability to detect our radio signature at great distances.

https://arxiv.org/pdf/1207.5540.pdf

For example, the Arecibo Planetary Radar typically transmits at a power of 0.8 MW and a frequency of 2380 MHz, with a gain of ~108. This means that low bandwidth transmissions from Arecibo, with B ~ 0.1 Hz, would be detectable by a watcher with a 1 km2 receiving antenna at distances up to 200,000 light years, while high bandwidth signals, with B ~107 Hz, would be detectable out to about 5 light years by the same watcher.

By comparison, television carrier waves have similar power but gain ~10, B ~ 1 Hz, and frequencies in the range of 100 to 2700 MHz; such signals could be detected with a square kilometer array out to a distance of about 50 light years.

RIP Arecibo