Physics in The Book of the New Sun

a series of novels by Gene Wolfe

This ship which sails between the stars... After ascending to the throne, Severian the autarch must journey between the stars to reach those who will judge him and humanity, and petition them to allow him to bring the New Sun. He finds himself on a space ship, which Severian describes in terms that might be used to describe an ordinary sailing ship, and in doing so reveals many physical facts.

"The great decks are flat, so that a sailor on one part can signal to his mate some distace away; if they are curved, with surfaces everywhere equidistant from the hunger of the ship, separated hands would be concealed from each other, as ships were hidden from one another under the horizons of Urth. But because they are flat, they seem always to slant, unless one stands at the center. Thus I felt, light though I was, that I climbed a ghostly hill."

Thus on an object much smaller than Urth, Severian is introduced to dealing with gravity as acting in the direction of the center of mass (of the "hunger" of the ship), rather than simply down. Any two objects placed a finite distance apart on a line which does not pass through the center of mass would then find gravity acting on them at different angles to that line. A flat surface that feels level at one point would feel slanted at another.

"Because I felt my whole being but a tissue of feathers, I had supposed I would rise slowly, floating upward as I had been told sailors floated in the rigging. It was not so. I leaped as swiftly and perhaps more swiftly than anyone here on Ushas, but I did not slow, as such a leaper begins to slow almost at once. The first speed of my leap endured unabated - up and up I shot, and the feeling was wonderful and terrifying."

Here Severian finds himself verifying that an object (himself) set in motion will stay in motion unless a force is acting upon it. In his case, the force (gravity) is very slight.

"Absurd though it seemed, I somehow felt that my weight, which had been only slight on the tier of my cabin diminished further as I descended. Earlier, when I had climbed the rigging, I had noticed that it dwindled as I ascended; it therefore followed that it should increase as I moved down from level to level in the bowels of the ship. I can only say that it was not so, or at least that it did not seem so to me, but the very reverse of that."

This is perhaps the most interesting case of physics in the book, because it demonstrates the limit of Severian's knowledge. As he climbed away from the ship on the rigging, he would have felt a smaller gravitational force because the force of gravity declines in inverse proportion the square of distance. However, the force of gravity is also proportional to the masses involved. As Severian descends into the ship, he has put more of its mass "above" him, acting in the opposite direction of the total force of gravity, counteracting some of the force generated by the mass below him. As a result, his weight decreases both as he rises from the surface of the ship, and as he descends below the surface of the ship.