What if most civilisations either destroy themselves or are wiped out by a comet or changing star conditions or an irregular orbit, or any number of things. If

What if most civilisations either destroy themselves or are wiped out by a comet or changing star conditions or an irregular orbit, or any number of things. If life truly does take as much time to become intelligent enough to actually tackle space travel there is a lot that can go wrong in the 4 billion year interim. Plus that requirement rules out a great number of stars which don't live long enough. Even our civilisation, any number of things could still go wrong before we are able to explore the universe. I wouldn't be surprised if we find a decent amount of life of the single cell variety. There is also the possibility of a civilisation far older than ours that never really got going on the intelligence path, or are lacking a good supply or certain base materials to really get going.