This will be what I believe to be my best post. It is a thought experiment.
Imagine you step out of a cave into a forest. It is a dense forest with fog obscuring your sight.
You decide to explore this forest. You walk underneath and between the big trees for a while, until you find yourself suddenly swallowed whole by the fog. Everything turns black.
When the fog lifts you find yourself right where you started, in front of the cave you had previously exited. You walk into a different direction, you make some progress until the fog swallows you and transports you back again. Whatever direction you try, you experience the same outcome. It seems like you’re doomed to never get anywhere.
That is until you notice fluorescent arrows on the ground, like emergency lights in airplanes.
When you walk on these lines, the fog does not swallow you whole. You follow the lights for miles on end – it seems like the lines are all interconnected with one another. You start making a map of this strange place. The map turns out to be ovally shaped, like a dome.
Using this map you travel to what is logically the edge of the forest, expecting to see something befitting the end of your world, something like this:
But instead there is nothing. Just more trees, fog and lines that curve backwards. If you step out of bounds, the fog swallows you once again and teleports you to where you started. What is out there, beyond the edge of what you can reach?
The answer is simple for those of us who know the story: if you were able to look from the outside in, you would see a purple dome floating through space.
But you can never take a look from outside in – you are stuck inside the forest. The best you can do is reason that a thing such as the purple dome exists and that it always lingers just beyond your reach, containing everything. Mankind has done exactly this for centuries. Only they didn’t call it the purple dome, they called it God.