Woof! Did you know that Lassie was a boy dog. Male dogs are better looking more photogenic. Not many people know that.
But back to the subject, Grimco's process of elimination can only lead to one conclusion. The final number of civilizations is one: US! We are the one and only sentient life in the Galaxy.
This does allow the religious among us to bring God into the calculation however absurd and fictional that notion is. But each to his own.
The problem with this whole topic is that no matter how much evidence and scientific observation there is, some people prefer either to not think about it all or invent some spurious story that fits in with their beliefs.
But when you think about it the whole subject topples the brain's gyros. Think about it. The universe must have existed forever in some form because if it didn't there would be nothing, not even nothing. Even in it's compressed pre big bang form it existed. If you believe in God, he had to have existed forever too and only lately (relatively) invented the whole universe notion.
Aaaaaah it's too complicated.
But of course there is no such thing as time, we humans invented it to mark the day and navigate across the oceans. No other creature is aware of it or indeed is aware of their mortality. Life and everthing else is simply a cycle of growth and decay followed by another cycle of growth and decay. We humans see ourselves as individuals and having importance in ourselves, thus deserving continued existence. So we invent a God and an afterlife and grant immortality to ourselves. In reality the only slight immortality we might have is to pass on our genes to the next generation and hope they have a better life. Even the most religious can agree that is the fate of all other living organisms. But we cannot accept that truth for ourselves because it means we have no future beyond what we see and feel right now.
If there is a God, it is the universe itself, infinite beautiful and pitiless. It created us and will destroy us in time, which of course it has no concept of.
Whew too heavy, on a lighter note. Did you know that a spinning gyro attempts to maintain it's position in space. So as the Earth moves through space it topples towards the point in space where it started spinning. Not many people know that either.