Curved-space robot defies known laws of physics
The discovery has implications for locomotion without propulsion.
Arobot engineered at Georgia Institute of Technology (Georgia
Tech) has done the unthinkable and flouted a steadfast law of motion, suggesting that new laws need to be defined. Such new principles may have applications in new forms of locomotion without propellants.
Newton’s third law states that for every action there is an equal and opposite reaction. So, when a human takes a step, we push against the Earth and the Earth pushes back, propelling us forward. But this only works thanks to friction. Without friction (or with minimal friction, for example, when there’s a banana peel on the ground) there is no push – we just slide straight over the ground and can’t move forward, instead falling back to Earth.
The same is true of locomotion. Rockets, for example, eject massive amounts of matter at high speed to push themselves in the opposite direction. Animals in the sea and air push against water and atmosphere respectively. There is always a push to move.
We generally think of space in terms of what are called Cartesian coordinates – the x-, y- and z-axes of three-dimensional coordinate space that we all used in high school. These axes all jut out from an ‘origin point’ at right angles to each other and continue ad infinitum in straight lines.
But space can be visualised as curved as well.
In a study published in PNAS, a robot has bypassed the need for a thrust in order to change momentum by making use of curved space.
“We let our shape-changing object move on the simplest curved space, a sphere, to systematically study the motion in curved space,” says lead researcher Zeb Rocklin, assistant professor in the School of Physics at Georgia Tech.
“We learned that the predicted effect, which was so counter-intuitive it was dismissed by some physicists, indeed occurred: as the robot changed its shape, it inched forward around the sphere in a way that could not be attributed to environmental interactions.”
To make sure that the effects induced by the curvature of the robot’s space dominated, the physicists had to isolate the system as much as possible from external forces.
The curved space was produced by placing a set of motors on curved tracks, attached to a rotating shaft to produce a spherical space.
Friction was curtailed using air bearings and bushings – lowheat and low-mess alternatives to ball bearings. Gravity was diminished by aligning the rotating shaft with Earth’s gravity.
Although only slight, friction and gravity were seen to hybridise with the curvature of the space itself to produce a strange dynamic with properties that could not have been produced by either friction or gravity on their own. So, the team demonstrated not only how curved space can be realised, but also how it fundamentally challenges basic concepts attributed to the laws of flat space.
“This research also relates to the ‘Impossible Engine’ study,” says 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.”