ConwayLife.com

Is there a proof that a glider outside of a bounding diamond of rest of the pattern (finite or infinite) never interacts with rest of the pattern?

A glider facing Northeast is at coordinate (N, N), and the board above the line x = -y is empty except that glider.

My conjecture is that if N is large enough, regardless of the state below x = -y, the glider is never interfered. This kind of proof could have been done by early life pioneers when ...