Death's End (Remembrance of Earth’s Past, #3)

by Liu Cixin

Later, there was a more moderate and localized proposal for taking advantage of curved space for navigation. Supposing a spaceship could somehow iron flat the space behind it and decrease its curvature, the more curved space in front of it would pull it forward. This was the idea of curvature propulsion. Unlike folding space, curvature propulsion couldn’t get a spaceship to its destination instantaneously, but it would be possible to drive it asymptotically to the speed of light. Until Yun Tianming’s message had been correctly interpreted, curvature propulsion remained a dream, like hundreds of other proposals for lightspeed spaceflight. No one knew whether it was possible at either a theory or practice level.