> And there are many "interesting" star-systems within 100 LY, so in those cases perhaps extinction isn't an issue.
No, in that case, timing is.
FWIW, I'm operating under a dystopian and pessimistic assumption that any civilization will destroy itself within a few thousand years of discovering radio. At some point, there will be massive wars over dwindling resources and eventually a weapon (or the combined power of multiple weapons) causes so much damage that it ends up wiping out all life on the planet.
This means that a civilization will only broadcast a signal for other planets to pick up for a few thousand years. In a galactic scale, that's incredibly short. It's basically the blink of an eye.
I share your view that broadcasting radio waves is a time-limited phase in human development; the airwaves are limited. But I don't agree with you that it could last "a few thousand years"; radio broadcasting depends critically on an electronics industry that only works at scale. Those industries depend on a stable, modern civilization, and I see no reason to think that modern civilization should last longer than earlier civilizations.
I completely agree that the duration during which a civililization can be expected to broadcast radio is extremely short, in galactic terms. So I think the likelihood is that if you do detect a radio transmission from outside the Solar System, by the time you receive it, the sender is dead; all his descendants have died; his planet's climate has changed, so that his species has been compelled to evolve (or die out); and his electronics-supporting civilization is long gone.
No, in that case, timing is.
FWIW, I'm operating under a dystopian and pessimistic assumption that any civilization will destroy itself within a few thousand years of discovering radio. At some point, there will be massive wars over dwindling resources and eventually a weapon (or the combined power of multiple weapons) causes so much damage that it ends up wiping out all life on the planet.
This means that a civilization will only broadcast a signal for other planets to pick up for a few thousand years. In a galactic scale, that's incredibly short. It's basically the blink of an eye.