Self-Fixing Universe

As soon as we developed time travel that worked backwards, the debates began about what would happen if we tried to change history. Our first subtle attempts seemed to indicate a self-fixing universe, or possibly a predestined one, given that trying to alter a result seemed instead to confirm it.

But the discussions were long about how we could test things without risking everything, until Dr Jackson grabbed a gun and went back to shoot his grandfather.

When Dr Johnson returned with a story of the gunshot magically hitting someone other than his grandfather, we settled on the predestined theory.