... and if you are more clever, you can even simulate dynamic interactions going on, out of the occlusion culled render window, between various systems and actors.

A whole, invisible, living world, doing its thing, without you.

Or...

... is it really just temporarily invisible?

When you dream of being a butterfly... do you not see the world of the butterfly?

The world of the dreamer, well, now that's invisible, beyond the experience of the butterfly dreamer.

Perception is indeed in the eye of the beholder; the nature of reality can be more of an ontological, or even etymylogical question, than a practical one.