It's not a new idea—the concept was used with the Genesis spacecraft mission—but scientists are now attempting to actually map out the tube-like gravitational currents in space. Didn't someone think of this in a TV show or two?
The idea is that travelling by way of these gravitational currents would save drastically on fuel, as it would only be needed to correct course or move between currents. Sadly, it's not exactly a fast way to travel and "attempting to get a free tube ride from Earth to Mars would take thousands of years". Ah, well. At least it proves that some sci-fi writers weren't complete nutters. [Telegraph]