Original sentence: How this works is never explained, but implies the idea of some universal defense mechanism.If the portal were still open when this happened, it would destroy the primary universe and all of spacetime.This creates an unstable parallel (or tangent) universe which will cease to exist at the end of those 28 days if the engine is not returned to the primary universe
Edited sentence: How this works is never explained, but the idea of a universal defense mechanism is an intriguing one, and perhaps the ultimate macrocosm of self-preservation.If the portal is still open when this happens, it would destroy the primary universe and all of spacetime.This creates an unstable parallel (or tangent) universe which will cease to exist—in 28 days—if the engine is not returned to the primary universe