As humans, animals and machines move around the world, they always obey the law of conservation of momentum. even though,Scientists at the Georgia Institute of Technology have now proven the opposite—it turns out that when objects exist in curved space, they can actually move without obeying that law.

The findings were published July 28 in the Proceedings of the National Academy of Sciences. In this paper, a group of scientists have created a robot that is confined to a spherical surface with unprecedented isolation from its environment, so that the effects caused by these curvatures are dominated. The researchers were led by Seb Rocklin, an associate professor in Georgia Tech’s School of Physics.

“Our shape-changing materials travel over a sphere, the simplest curved surface to systematically study motion in curved space,” Rocklin said. “We realized that the predicted effect occurred, which some physicists had dismissed as being very counterintuitive: when the robot changed its shape, it bent itself in such a way that it didn’t react to the environment. It moved forward.”

Make a curved path

Scientists began to study how an object moves in curved space. It is necessary to confine the object to a sphere where there is minimal interaction or momentum transfer with the environment in a curved space. To do this, they had a set of motors that acted as a moving mass to drive on a curved track. Then they connected the whole system to a rotating shaft that kept the motor moving on a sphere all the time. To reduce friction, the shaft is supported by air bearings and bushings. To reduce the residual force of gravity, the alignment of the axes is adjusted to align with the Earth’s gravity.

From then on, as the robot moved, gravity and friction exerted a slight force on it. These forces combine with curvature effects to create a peculiar dynamic that neither alone can account for. This research provides an important demonstration of how curved space is achieved and fundamentally challenges the laws of physics and intuition designed for flat spaces. Rocklin hopes the experimental techniques developed will allow other researchers to explore these curved spaces.

Space and other applications

Although the effect is small, understanding the effects of this curvature may have practical implications as robotics become more precise, as the slight frequency shift caused by gravity becomes crucial for a GPS system to accurately communicate its position to orbiting satellites. Ultimately, the principles of how to harness the curvature of space for motion may allow spacecraft to navigate the highly curved space around black holes.

“This study ties in with the ‘Impossible Engine’ study,” Rocklin said. “Its creators claim it can propel itself without any propellant. That engine is certainly impossible, but because of the very small curvature of spacetime, a device can actually propel itself without any external force or propellant. Propulsion without compromise — that’s the new discovery.”