Our radio emissions aren't that visible, there is a horizon, so to speak, where your radio signals attenuate to be indistinguishable from background radiation. For our TV transmissions I believe this to be no more than a handful of light years. As tech has been increasing we've been putting less power into our transmissions and thus reducing that horizon. Even high powered military radars aren't typically banging away into the sky in the same way they used to.
Then you've got the fact that the env for coms has been becoming increasingly hostile anyway. Long term quantum computing is pretty much a certainty, and when that happens quantum encryption seems like it's going to be the only workable form of coms for anything you want to keep quiet. Even if you assume that in the West it'll only be places like NSA and GCHQ and so on who have one - China's going to have one too, and do you really think they're not going to use it against commercial systems? People will have to move to quantum encryption - you're just not going to be able to do business without it.
So, I wouldn't expect us to keep using the airwaves very much. I expect the future of airwave use to be primarily relatively short ranged point to point transmissions.
The visibility for radio transmissions, even if humans survive a million years isn't, I think, going to be a million years, I'd expect it to be more like 100. Thus - though I don't know how they calculated their number - I'd make the back of the hand odds that someone examining our planet randomly would pick us out not 1 in 5,000 but, instead, 1 in 50,000,000.
And since we're not going to get 50,000,000 civilisations within the handful of lightyears before our signals have attenuated down to the background... I'd put the odds heavily against anyone seeing us on that basis.
Whether someone will pick up the composition of our atmosphere and aim a more powerful beam in our direction I don't know. But it makes it ... something that the other civilisation would have to decide to do. And then you're dealing with - does it actually make sense to let other civilisations know that you exist? What are your potential gains when balanced against the risk of relativistic weapons and the like?
Kraus's famous classic 'radio astronomy' textbook had some comments about this topic toward the end. If I recall correctly it was a couple light years for analog NTSC. Nice stable transmitter, satellite disciplined carrier freq toward the end, and the doppler as the earth rotates of a zillion signals gives the little green men something interesting to think about. Planetary radar, IF aimed directly at the target, had much better range, but analog NTSC television had much better coverage over the whole sky.
The radio detection of the earth by broadcast analog NTSC TV carriers has already ended. The article author specified it as a million years. We got about fifty instead. If the LGM are watching our analog TV carriers and the SNR is less than 20 dB or so, there is no way they'll see digital as a discrete signal, nor will they likely randomly guess the correct signalling types/codes.
The meta issue is as a species we're really good at thinking our time is special. 100 years ago watching a spectrogram of analog AM video carriers would have been unthinkable futuristic not even rational to discuss, 25 years ago it would have been a pretty good idea, today its ancient nothing but static, no body would do something so anachronistic.
This misbelief in the importance of your time is closely related to one of the funniest atheist arguments, which is so intellectually unthinkable its rarely discussed. Even the slightest gaze on religious history of the species shows that before the birth of a prophet or whatever, people really thought they had it all figured out almost as well as after. Because this mis-design-pattern has repeated itself with pretty much all religions in the past, I'm sure it will happen again in the future, so simply deciding to believe in nothing until the true prophet is born in 100000 years is the most rational decision. In fact over 100000 years we'll probably have about 100 prophets, all of which, however temporarily, being considered the last word in religion... Its sometimes called the patience atheist argument, or a few other things... Why, everyone knows the best and most important and most correct culture to ever exist, in the past, or more importantly in the future, is now, of course.
Then you've got the fact that the env for coms has been becoming increasingly hostile anyway. Long term quantum computing is pretty much a certainty, and when that happens quantum encryption seems like it's going to be the only workable form of coms for anything you want to keep quiet. Even if you assume that in the West it'll only be places like NSA and GCHQ and so on who have one - China's going to have one too, and do you really think they're not going to use it against commercial systems? People will have to move to quantum encryption - you're just not going to be able to do business without it.
So, I wouldn't expect us to keep using the airwaves very much. I expect the future of airwave use to be primarily relatively short ranged point to point transmissions.
The visibility for radio transmissions, even if humans survive a million years isn't, I think, going to be a million years, I'd expect it to be more like 100. Thus - though I don't know how they calculated their number - I'd make the back of the hand odds that someone examining our planet randomly would pick us out not 1 in 5,000 but, instead, 1 in 50,000,000.
And since we're not going to get 50,000,000 civilisations within the handful of lightyears before our signals have attenuated down to the background... I'd put the odds heavily against anyone seeing us on that basis.
Whether someone will pick up the composition of our atmosphere and aim a more powerful beam in our direction I don't know. But it makes it ... something that the other civilisation would have to decide to do. And then you're dealing with - does it actually make sense to let other civilisations know that you exist? What are your potential gains when balanced against the risk of relativistic weapons and the like?