Ah, but the problem is that given any reasonable odds of life developing, we would have heard radio noise by now. Even if we a million years behind the other civilizations, their transmissions from their equivalent of the 20th and 21st Centuries would still be echoing through the Universe. So where are they?
Ah, but the problem is that given any reasonable odds of life developing, we would have heard radio noise by now.
Highly unlikely.
Even if we a million years behind the other civilizations, their transmissions from their equivalent of the 20th and 21st Centuries would still be echoing through the Universe.
No they wouldn't, radio/TV transmissions don't "echo through the Universe". Even if they did, after the first few years they would be so attenuated (remember our old friend, the Inverse-Square Law?) that there's no way we would be able to detect them with current technology.
So where are they?
For most plausible values of the Drake Equation, they're too far away for us to "hear" or for them to come visit us.
Let's say there's somebody out there 100 light-years away. A broadcast they make registers as a million watts one hundred kilometers away (that's an absurdly powerful artificial signal). By the time it gets here, if I got my calculations right, the wattage at our end would be about 0.000000000000000112 watts, considering a perfect vacuum and no interference (a star between us). And we're supposed to detect that amid all the other electromagnetic radiation from closer and stronger natural sources? SETI is a fun exercise, but it's a shot in the dark.