Exploring Practical Applications of the "Warp-Drive" Theory

Exploring Practical Applications of the "Warp-Drive" Theory

Part 2: Time Travel and Subluminal Warp Drive

The concept of warp drive spacetime offers a fascinating approach to advanced transportation for timelike observers—those following a path through time. Key features of these spacetimes include the potential for acceleration along geodesic paths, superluminal travel (faster than light), and modified spacetime regions, all observed relative to external timelike observers.

However, classical warp drive spacetimes are challenging to realize due to their energy demands. Many of these configurations fail to meet all the established energy conditions, which raises doubts about their feasibility. This limitation has made the search for physical warp drive solutions through pure mathematics particularly slow and difficult, especially given the complexity of the Einstein field equations. Non-unit lapse functions and non-flat spatial metrics, elements that have been largely absent in previous models, add to these challenges.

One innovative solution is a "subluminal constant-velocity warp drive," which operates within a non-unit lapse and a non-flat spatial metric, while still satisfying all necessary energy conditions. This type of warp drive can be thought of as modifying a background spacetime that is both globally hyperbolic (causally consistent) and asymptotically flat, connecting two points along a non-geodesic path.

By altering the background spacetime, a warp drive spacetime could enable passengers to travel from point A to point B along a geodesic path without experiencing acceleration. This distinguishes it from trivial solutions where passengers would already be traveling between these points. A meaningful solution requires that passengers start at rest relative to point A, are transported to point B, and end at rest there as well.

To make this possible, the warp drive needs to maintain proper distances between A and B, measured within the background spacetime, with minimal alteration. This is achieved by enclosing passengers within a compact, vacuum region free of tidal forces.

Additionally, a spatially contained moving bubble represents a warp drive spacetime with a compact non-vacuum region surrounding the passenger path at every moment in time. This setup implies that the stress-energy distribution, essential for this geodesic travel, is confined within the bubble and travels with the passengers, rather than extending infinitely.

This conceptual framework brings us closer to understanding the practical dynamics of warp drives, particularly for subluminal, constant-velocity scenarios that could comply with the universe’s energy restrictions.