"Sapient window" is a term I have used before to describe the time period when intelligent beings on a planet have the knowledge base to realize the possibility of life existing elsewhere in the universe and the scientific wherewithal to search for it ... see:
Sapient Window. In this referenced link I estimate that, here on Earth we are now in our sapient window ... having been so for about a hundred years or so.
Being in this window, we are pouring resources into attempting then to discover life on other planets ... and to look for them contacting us and, maybe, eventually contacting them ... a naturally appealing idea. The largest radio telescope ever built ... partly to this end ... has just been activated ... see:
UK Mirror Story. So far this search has been to no avail using other means. As full of romantic agony this search entails, it is my contention that this quest is very likely to continue to be quixotic. (Stephen Hawking disagrees ... see:
CNET Story.) And my sad conclusion is simply based on three indisputable facts:
1) The likelihood that our sapient window, even were it to last for another 13 thousand years, would line up with the sapient window on some other inhabited exo-planet ... just in our galaxy alone ... is vanishingly small ... given the enormous span since the beginning of time (the Big Bang?) ... I calculate the probability of such alignments at 0,0001% (see:
Are We Alone?). Even if I am off by three orders of magnitude (because of things likely being back-end loaded), there is still only a one in a thousand chance of these sapient windows matching up.
2) The vast distances ... just in the galaxy in which our solar system exists, the Milky Way, let alone the Universe, are so large that the time delays imposed on any intelligent communications pretty much negate things ... even at the speed of light. We are talking about at least tens of thousands of years between any "Hello" and our excited response. This makes any meaningful communication pragmatically impossible.
3) it has been estimated that the energy required to send a receivable message of greeting over these vast interstellar distances could be equivalent to the energy output of our sun. I kind of doubt that this is realistically doable by all but a minuscule number of exo-planets with intelligent life, if any.
Thus, I again conclude that we are on a fool's errand with our attempt to wait for the phone to ring from another exo-planet ... and our possibly responding is even nuttier. The cost benefit analysis and actual science make no rational sense to this quest. I conclude that it is all just emotional pandering by scientists looking for more grant money.