On the grand macroscopic level what makes the bend in the paper is the gravitational properties of matter which curves space and time to its limits in a singularity or Black Hole. Singularities do not necessarily need to be the size of collapsed stars, but can be in the sub-atomic ranges of sizes. Some of the speculative areas of physics envision how space-time is a constant ferment of these singularities constantly coming into and out of existence all of the time, and creeating a wormhole bridging distant parts of the Universe or perhaps eveen different universes in related branes is a matter of expanding some of these quantum mechanical singularities.
One of the intriging questions is whether or not one of these hypothetical warp bubles would exhibit any physical dimensions within normal space-time or would it appear to disappear into a dimensionless point or singularity until the shutdown of the warp bubble?