That might not be the right question, or at least is isn't the only pertinent question. Other quesitons: "why can't we see the ones that are around now" and/or "what happened to the ones that aren't around now".
If we are detecting civilisations feom the RF output, then consider how quicly we went from no RF output to nearly blowing ourselves to bits. Many civilisations could have committed suicide in a short space of time too. Many millions of them could have shone breifly and vanished millions of years before we even started looking. That is a tad fatalistic: we haven't managed to wipe ourselves out even though we threatened it to an extent. But there is another good reason why an older civilisation would be difficult to detect: efficiency. As a civilisation's technology improves, unless they find an effectively unlimited energy source, it is likely that they will leak less and less out: communicating point-to-point methods most of the time rather than by broadcast, containing and reusing what would otherwise be waste products of enery production/use. Of course they would never be 100% efficient, but they only need to be efficient enough that by the time the side-effects of their activity reach us they are not descernable amongst the background noise from the stars, black holes and other parts of the cosmos.
Evidence of other life could be passing us by right now and our attmepts to detect it are simply insufficient, in fact the more civilisations there are out there the harder the problem could become: the signals from each would interfere making the attempt to spot any one signal amongst the background noise (in part natural noise and in part that from the other signals) that but harder.
It is all moot at the moment of course: unless they are on our doorstep, to the point where we couldn't miss them, meaningful communication in our lifetimes is very very unlikely.
Of course there are other equally possible explanations, such as us being in a simulation of sorts.
That might not be the right question, or at least is isn't the only pertinent question. Other quesitons: "why can't we see the ones that are around now" and/or "what happened to the ones that aren't around now".
If we are detecting civilisations feom the RF output, then consider how quicly we went from no RF output to nearly blowing ourselves to bits. Many civilisations could have committed suicide in a short space of time too. Many millions of them could have shone breifly and vanished millions of years before we even started looking. That is a tad fatalistic: we haven't managed to wipe ourselves out even though we threatened it to an extent. But there is another good reason why an older civilisation would be difficult to detect: efficiency. As a civilisation's technology improves, unless they find an effectively unlimited energy source, it is likely that they will leak less and less out: communicating point-to-point methods most of the time rather than by broadcast, containing and reusing what would otherwise be waste products of enery production/use. Of course they would never be 100% efficient, but they only need to be efficient enough that by the time the side-effects of their activity reach us they are not descernable amongst the background noise from the stars, black holes and other parts of the cosmos.
Evidence of other life could be passing us by right now and our attmepts to detect it are simply insufficient, in fact the more civilisations there are out there the harder the problem could become: the signals from each would interfere making the attempt to spot any one signal amongst the background noise (in part natural noise and in part that from the other signals) that but harder.
It is all moot at the moment of course: unless they are on our doorstep, to the point where we couldn't miss them, meaningful communication in our lifetimes is very very unlikely.
Of course there are other equally possible explanations, such as us being in a simulation of sorts.