My pet hypothesis: with the vast scale of the universe and the light-speed limitation, when it comes to potential conversational partners, the universe selects in favor of extremely long-lived life-forms (possibly "artificial"). Such life forms would be only be interested in interacting on highly protracted time scales; think "Space Ents". Given also that sending signals into deep space is extremely expensive and energy will always be finite, communication with new worlds is sought only rarely, perhaps one targeted ping per world every 10,000 years, each an attempt to start a dialogue to be carried out laboriously over millions of years.
I have two hypotheses, both untestable (and therefore worthless):
1. The distance between stars is too huge, so there has to be a trick to beating it easily, like FTL travel or wormholes, because otherwise it's just crap.
2. If any supervillains want to destroy the universe, they're too late: it's already been done, and this is all that's left.
> Given also that sending signals into deep space is extremely expensive and energy will always be finite, communication with new worlds is sought only rarely.
I totally agree to this statement. Even though I guess there is no need to actively sent too many information out in space as we do already have a kind of "frequency pollution" broadcasting TV channels, TCP packets etc. There are many signals travelling from earth to space all the time - communication with satellites doesn't end on them, remember: it's radio we use for communication!
You can easily imagine what it must be outta there when aiming at the earth with some kind of antenna: just imagine a world on which air isn't throttling voice-signals (aka shouting/talking). Those signals would keep floating around until they are reflected by some kind of object. Well, in space there aren't that many objects so our little earth is already looking like a big frequency mess and a kind of big light bulb for other guys out there. We just have to wait until all our civilization-generated signals are arriving at other parts of the galaxy.'
You can argue whether this is a wise thing to do this so naively but it's already too late to stop this from happening and to be honest: we can only do assumptions based on things we do know, so we simply have to speculate when it comes to aliens. The only thing which makes me a kind of sad is, that we humans seem to had a quite clear pattern when it comes to "exploration" of new geographical areas by external people (Northern/Southern American Natives, Africans, Australian Natives the list goes on and on). In this sense it's quite good that space-travels are that hard to do over a fast distance.
