Georgia Tech researchers defy standard laws of physics

Researchers have proven that when bodies exist in curved spaces, they can actually move without pushing against anything.

Robotic movement in curved space defies standard laws of physics

When humans, animals, and machines move through the world, they are always pushing against something, like the ground, air, or water. Until recently, physicists thought it was a constant, following the law of conservation momentum. However, scientists from the Georgia Institute of Technology (Georgia Tech) have now proven the opposite – when bodies exist in curved spaces, it turns out that they box actually move without pushing against anything.

These results were published on July 28, 2022 in Proceedings of the National Academy of Sciences. In the paper, a team of scientists created a robot confined to a spherical surface with unprecedented levels of isolation from its environment, so that these curvature-induced effects predominate. The researchers were led by Zeb Rocklin, an assistant professor in the Georgia Tech School of Physics.

“We let our shape-changing object move on the simplest curved space, a sphere, to systematically study motion in curved space,” Rocklin said. “We learned that the predicted effect, which was so counterintuitive that it was dismissed by some physicists, actually happened: when the robot changed shape, it moved slowly around the sphere of a way that could not be attributed to environmental interactions.”

Experimental Realization Swimmer on Sphere

Experimental realization of a swimmer on a sphere with motors driven on a freely rotating pole. Credit: Georgia Tech

Creating a Curved Path

Scientists set out to study how an object moves through curved space. They needed to confine the object to the sphere with minimal interaction or exchange of momentum with the environment in the curved space. To do this, they let a set of motors run on curved tracks like moving masses. Then they holistically connected this system to a rotating shaft so that the motors always move on a sphere. To minimize friction, the shaft was supported by air bearings and bushings. To minimize the residual force of gravity, the alignment of the shaft was adjusted with Earth’s gravity.

From there, as the robot continued to move, gravity and friction exerted slight forces on it. These forces hybridized with curvature effects to produce strange dynamics with properties that neither could induce by itself. The research provides an important demonstration of how curved spaces can be achieved and how this fundamentally challenges physical laws and intuition designed for flat space. Rocklin hopes that the experimental techniques developed will allow other researchers to explore these curved spaces.

Applications in space and beyond

Although the effects are small, as robotics becomes increasingly precise, understanding this curvature-induced effect may be of practical importance, just as the slight gravity-induced frequency shift has become crucial in enabling GPS systems to accurately transmit their positions to orbiting satellites. Ultimately, the principles of how the curvature of a space can be exploited for locomotion can allow spacecraft to navigate the highly curved space around a[{” attribute=””>black hole.

“This research also relates to the ‘Impossible Engine’ study,” said Rocklin. “Its creator claimed that it could move forward without any propellant. That engine was indeed impossible, but because spacetime is very slightly curved, a device could actually move forward without any external forces or emitting a propellant – a novel discovery.”

Reference: “Locomotion without force, and impulse via dissipation: Robotic swimming in curved space via geometric phase” by Shengkai Li, Tianyu Wang, Velin H. Kojouharov, James McInerney, Enes Aydin, Yasemin Ozkan-Aydin, Daniel I. Goldman and D. Zeb Rocklin, 28 July 2022, Proceedings of the National Academy of Science.
DOI: 10.1073/pnas.2200924119

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