Robot motion in curved space violates standard laws of physics

Robot motion in curved space violates standard laws of physics

Experimental implementation of a swimmer on a sphere with a drive motor on a freely rotating cantilever.Credit: Georgia Institute of Technology

As humans, animals, and machines move around the world, they always push on something, whether it’s ground, air, or water. Until recently, physicists thought it was a constant, obeying the law of conservation of momentum. Now, researchers at Georgia Tech have demonstrated the opposite — when objects exist in curved space, it turns out they can actually move without pushing on something.

The findings were published in Proceedings of the National Academy of Sciences July 28, 2022. In the paper, a team of researchers led by Zeb Rocklin, an assistant professor in Georgia Tech’s School of Physics, has created a robot confined to a spherical surface that is isolated from its environment to an unprecedented degree, so the effects caused by these curvatures will dominate. .

“We made our deformable object move over the simplest curved space (a sphere) to systematically study motion in curved space,” Rocklin said. “We learned that the predicted effect did occur, which was so counterintuitive that it was dismissed by some physicists: as the robot changed shape, it moved forward around the sphere in a way that could not be attributed to environmental interactions. move.”

Create curved paths

The researchers set out to study how objects move in curved space. To confine the object to a sphere with minimal interaction or momentum exchange with the environment in curved space, they had a set of motors act as a moving mass to drive on a curved orbit. They then attached the system as a whole to a rotating shaft so that the motor always moved on the sphere. The shaft is supported by air bearings and bushings to minimize friction, and the alignment of the shaft is adjusted to earth gravity to minimize residual gravity.

From there, gravity and friction exert a slight force on the robot as it continues to move. These forces mix with curvature effects to create a strange dynamic, none of which can be induced on its own. The research provides an important demonstration of how curved space can be obtained and how it can fundamentally challenge the laws of physics and intuitions designed for flat spaces. Rocklin hopes to develop experimental techniques that will allow other researchers to explore these curved spaces.

Applications in space and beyond

Although the effect is small, as robotics becomes more precise, understanding this curvature-induced effect may have practical implications, just as a slight frequency shift caused by gravity is essential for allowing GPS systems to accurately transmit their position to orbiting satellites crucial as well. Ultimately, principles of how to exploit the curvature of space for motion may allow spacecraft to navigate the highly curved space around black holes.

“This study is also related to the ‘Impossible Engine’ study,” Rocklin said. “Its creators claim that it can move forward without any propellant. That engine is indeed impossible, but because spacetime is very slightly curved, a device can actually move without any external force or propellant. Down and forward – this is a new discovery.”

Free-Space Optical Coupling Using Curved Micromirrors

More information:
Li Shengkai et al., Robotic swimming in curved space through geometric phase, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2200924119

Courtesy of Georgia Tech

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