Variables and variables
An interesting and unheard argument against time travel by Caleb Scharf.

Scharf points out: If you want to move around in time, you need to solve a simpler problem BEFORE you can deal with the contradictions of time itself. First you have to know WHERE you'll land. Since every point on earth is constantly rotating and moving in an infinite number of cycles and patterns, even a one-day trip requires billions of miles of impossible-to-predict movement.

Sci-fi never** tries to handle this question, instead tacitly assuming that you can 'pin' the Tardis to a specific place, like pegging a tent to the ground.

When you look more closely at pegging, it gets tricky. A house stays in one place by electrostatic attractions and repulsions between the trillions of atoms of its foundation and the trillions of atoms in the nearby soil. Those atoms and electrons change places constantly, but the change is slow enough that the attractions and repulsions can readjust. When atom #123456734512 reacts chemically and loses its bond, millions of nearby atoms are still holding steady.

This numerical overwhelming would fail when you slide around in time. After a month or so, the atoms of the ground under the Tardis have all changed and moved***, and they no longer have any relationship with the atoms of the Tardis. You could set it down again, but now you're not pegging. You're back in Scharf's unpredictable movement scenario.

= = = = =



**Sci-fi writers do sometimes worry about the location. What if a house is built on the spot before you land, or the spot is now underwater, or the planet has been sucked into a black hole? But they don't try to analyze the essential problem with 'pegging'.

***And this isn't even mentioning the BIG FAST moves caused by bacteria, earthworms, frost, moisture, plant roots, gophers and insects.
  ¶ 2:38 AM