Is the Universe a Closed System?

My wife and I and our three children lived for a number of years amongst the Danis in West Papua. Like many tribal societies the Danis were largely self-sufficient; almost everything they needed was available in the environment around them. They grew their own sweet potato, raised their own pigs, got their water from nearby springs, made their net bags from plant fibres and heated their huts and cooked with wood from the casuarina trees they planted in their old gardens. Swampy ground provided the reeds for the women’s skirts; the gourds used to clothe the men were grown in the village compound. In the past they lived a claustrophobic life with enemies on all sides, and they rarely, if ever, wanted or needed to leave their own tribal homeland.

What about the universe? Is it a self-sufficient, self-contained system? Those who believe in naturalism are sure that it is. Atheists along with pantheists think that this universe is all there is, that everything can be explained in terms…