Wormholes
Is there any hope of our building a time machine that the universe won't destroy before we can use it to travel back in time? Yes, there is hope in the form of wormholes. Theories of wormholes predate black holes. Within a year of Einstein's final publishing of the general theory of relativity physicist Ludwig Flamm recognized that Schwarzschild`s solution represented a wormhole. A wormhole is a tunnel through hyperspace to another region of spacetime in our universe or perhaps another (see figure 3). The wormhole consists of two mouths that are spherically symmetric and a throat that has a maximum radius equal to its Schwarzschild radius. There are two kinds of wormholes, those that will be useful to us aspiring time travelers and those that will not.
Figure 3: A 1 km Wormhole through Hyperspace linking Earth to the star Vega, 26 light-years away