GPS is vital to modern navigation, but it's extremely fragile. Never mind coverage -- if a satellite fails or there's a jamming attack, it quickly becomes useless. Scientists may have a much more robust answer, though. Scientists have demonstrated a "commercially viable" quantum accelerometer that could provide navigation without GPS or other satellite technology. The device uses lasers to cool atoms to extremely low temperatures, and then measures the quantum wave properties of those atoms as they respond to acceleration.
The result is an extremely sensitive device that's also considerably more reliable than conventional accelerometers. While existing hardware can help determine to location to some extent by measuring velocity, it quickly falls apart without help from space.
As you might have noticed by looking at the photo above, this quantum 'compass' isn't ready to replace the accelerometer in your phone. It's only truly ready for ships, trains and other large vehicles where size and power requirements aren't major factors. It could keep transportation networks humming even if GPS fails outright. The researchers also expect the underlying concepts to help with science studies, such as looking for gravitational waves.