I think everyone on this board is familiar with Fermi's Paradox: If life is so common (specifically intelligent life), why don't we see more of it? There are a number of explanations, but my simple question is...is the science we use to even understand whether there is life on other planets even past its infancy enough to reliably determine whether it really exists? In other words, while we can somewhat safely determine there are no direct human analogues using radio transmission in Alpha Centauri, are the techniques we use to determine the viability of life things like it on other celestial bodies advanced enough to even say one way or the other? Let us presume for a moment that there are tens of thousands of planets with lifeforms in a fairly medieval society, what scientific instruments and techniques do we have that could even really determine whether they existed on any planet, let alone reliably estimate how many of them there are in the galaxy, or that there appear to be none in the first place?