To be fair, it's is not impossible there is such a civilization out there, but we haven't been able to observe them yet because they are so far away no signals or other evidence of their exploits has reached us in the short time we've had the ability to detect them. Or, it is also possible their signals have actually reached us ... a million years ago and they have gone extinct in the time it took those signals to reach us or perhaps they started communicating through means we can't detect (yet).Silentpony said:The signs that humans are on Earth are irreparably clear. If aliens were even more advanced than us they'd be a beacon for half the galaxy. Dyson spheres, mining of asteroids, planet-to-planet transmissions, inevitable cosmic wars, signs of system wide colonization. They'd have seen it in the 50s with the first radio telescopes.
I'm not saying there are alien civilizations out there, just that our inability to find any in the very short time we've been able to observe a tiny amount of the universe does not mean the possibility of them existing (or having existed) is zero. The universe is very big and very old. Plenty of time and space for civilizations to have risen and fallen beyond our ken.