So where are they? Those teeming alien hordes that SETI has spent fifty years looking for? I'm going to suggest something, something really whacky, really off the wall - but maybe, just maybe, it's in with a chance...
Let's suppose, just for one moment, that radio signals obey the same rules out there as they do here. If you send a signal in every direction at once, it's spread pretty thin and you can't detect it after just a few thousand kilometers at best. So any alien civilisation that's broadcasting a signal strong enough for us to pick up a billion parsecs away has to be burning through an average sized sun's worth of fissionables every few centuries.
The other way to improve the strength and range of your signal is to focus all that energy into a beam. And what are the chances that an alien civilisation is pointing a radio beam right at us? Right.
Professor Davies thinks much the same. He also suggests that we need to look at a much broader frame of reference if we're to find any evidence of those elusive green people. I suggest that even he's maybe not looking at a wide enough frame yet...
For a starters - if I wanted an alien civilisation to find out about me, I'd probably not bother to leave a radio beacon around. Just not worth the effort. Also, to be quite honest, quite primitive for my tastes. If I'm at that stage where I contact another alien (or alien civilisation) then I'd be using a much more permanent beacon. Like, maybe, I'd leave a 3D hologram of my civilisation.
Maybe the reason we're not seeing a message is because we are the message...
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