Which should have led him to the conclusion that 'physically' searching by traveling through the universe is not the solution to having a good change of finding life?

Unless we figure out a fundamentally different way of space travel there's no way we will ever be able to search everywhere within an acceptable time-frame. As exotic as it might be, I think self replicating probes, as in exponentially increasing numbers of probes would still be the best way of searching when you're considering using not-so-sci-fi methods of propulsion and so on.