Before I begin, let me preface by saying this post isn't about ancient astronauts. It's about the God of the Gap, the theological perspective that the supernatural merely occupies the gaps in our scientific understanding of the universe.
It's generally used in the pejorative sense by both sides of the atheist/believer divide. One might exclaim, "Shame on the believer who limits the almighty creator to a shrinking gulf of human ignorance!" Another might say,"Shame on the believer who invests in an increasingly archaic cosmological model."
It's god with a lowercase "g" for sure.
This gets more interesting when we bring in the writings of noted skeptic Michael Shermer, who half-jokingly introduced the idea of Shermer's Last Law:
This is of course a take on Arthur C. Clarke's famous Third Law:
For the sake of argument, is God an entity of this universe or something outside of it? Anything based in reality must correspond to our scientific understanding of it. And given the vastness of space and our own evolutionary model, an alien species one-million-years ahead of us might well fill the role of "God."
But most people don't want to worship an alien. They want something supernatural - and a supernatural entity that exists outside of nature is, by definition, unknowable to science. But if it reaches into our world to mess with things, then that reach must be measurable by science.
So we look for the Hand of God, or more particularly the particles it would have to stir. We're still waiting for the evidence.
On a Personal Note
For what it's worth, I'm not an atheist. I try to keep science and reason as the bedrock of my world view, but I like engaging other perspectives, I like questioning everything and I like to build my own plate from the great salad bar of belief. Choose what works. Pick the teleological items that bring you closer to people and nearer to peace. So I believe that a godlike ETI might well exist in the universe, but I don't think this diminishes the concept of a supernatural personal God. But that's just my two cents...
About the Art Choice
My initial plan was to crop the image so as to focus on the otherworldly vision of the divine, but the painting deserves better than that in my view. It captures a fanatic vision of a bridge between natural impermanence and the supernatural permanence.