Sometimes I simply have far too much fun writing stories.....most recently, at Moon Hammer, I needed to add a religious scientist to the plot, so I decided to include Isaac Newton. It is fun to imagine what he might have done is given an "afterlife".
Newton was apparently the first person to realize that the same force (gravity) that makes an object (such as an apple) fall on Earth is what holds the Moon in the sky. Newton was well aware of the fact that earlier thinkers such as Galileo had rejected Aristotle's claim that heavy objects fall faster than lighter ones. Both Newton and Galileo would have been thrilled to watch the Apollo "moon hammer" experiment (see the video to right).
However, putting Newton on the Moon raises a serious issue. Surely Newton would notice the lower gravity on the Moon and he would not be satisfied to simply assume that in Purgatory, part way between Earth and Heaven, people should just naturally be lighter. Where would Newton imagine Purgatory to be? Dante imagined the Mountain of Purgatory and placed Hell at the center of the Earth. I've seen it claimed that others such as Robert Bellarmine, the fellow who had the job of telling Galileo to abandon belief in heliocentrism (and who helped burn another believer in heliocentrism, Giordano Bruno), taught that Purgatory was inside the Earth.
Ever since seeing Journey to the Center of the Earth on television when I was young, I've been puzzled by people who imagine that there are places to visit deep under the surface of our planet. I've seen it claimed that Newton's early estimate for the density of the Earth (less dense than the Moon!) led other people (example) to explore the idea that the Earth might be hollow or have large internal spaces not filled by hot rock. I think I am close to deciding that the residents of Purgatory in Moon Hammer will mostly be believers in the idea that they are somewhere deep inside the Earth. I have not yet found a claim that Newton thought along those lines. Newton later gave better estimates of the density of the Earth and the Moon. I think the Shell theorem says that if you moved down into a hollow Earth then the force of gravity would decrease. I've seen it claimed that descending towards the center of the Earth actually results in a greater weight because the density of the Earth increases towards the center. However, I think that discovery of the dense, metal-rich core of the Earth was a relatively recent discovery. If the robots of Purgatory adopted the belief that they were inside the Earth, would later scientific discoveries cause them to change their thinking? In any case, all bets are off if the Overseers actively work to prevent the robots of Purgatory from discovering their location.
I enjoy imagining hidden underground bases on the Moon. There are some stories in which it is imagined that Earth is orbited by a Hollow Moon. One of the most interesting proposals I have seen is the Spaceship Moon Theory. I've tried searching for previous mention of the idea of Purgatory being located on (or inside) the Moon, but I have not found anything along those lines.