Isn't the assumption just that alien life has reached the ability to listen for signals before we reached the ability to send them (and that they're still alive)? Or even that they reached the ability to listen for them some time after we started sending them but before we started listening for them.
Yes, but I am suggesting that the assumption is highly unlikely, given the low chances of two civilisations (ours and theirs) reaching this point simultaneously, given the massive age of the universe.
If the Earth's entire history up until now is reduced to a single day, then our technological civilisation has only existed for the last few seconds before midnight. It seems unlikely that the civilisation next door also coincidentally appeared in the same few seconds.
