Scientists unveil a physics-defying curved space robot
It can move without anything to push off from, but only via curved spacetime
A team of scientists from Georgia Tech say they've built a robot that can move without anything to push against – a discovery that seems to violate the law of conservation momentum.
The researchers were able to generate momentum without a surface to push off from by building a robot isolated from outside influences and confined to a curved space. In a video the machine can be seen shifting a pair of motors attached to a piece of curved track, slowly moving itself without any external force.
"What our research demonstrates is that it's possible to acquire a sort of velocity, and hence move forward, without acquiring any momentum," senior author and Georgia Tech assistant physics professor Zeb Rocklin told The Register. This was a team effort, he emphasized, acknowledging the work of first author Shengkai Li.
"The caveat, though, is that this is only possible in a curved spacetime. We supplied the curvature by sticking our robot on a sphere."
Curved space is a fundamental part of modern physics, and is essential to understanding general relativity. For humans, who move in three relatively flat dimensions, Newton's third law dictates that each force has an equal and opposite one. This is how rockets get their thrust, how we're able to jump, and how cars move down the road.
In curved space, forces differ; In their paper, the team said that objects in curved space should theoretically be able to move without frictional or gravitational forces.
To minimize the influence of flat space physics on the robot, the team mounted it to a shaft supported by air bearings and bushings. The shaft was also aligned to earth's gravity to eliminate residual force.
The robot did face slight frictional and gravitational forces, which hybridized with the curvature of its track "to produce a strange dynamic with properties neither could induce on their own," Georgia Tech said. According to the institution, the forces on the robot during the tests were predominantly due to its curved environment.
What do you do with a curved-space robot?
Watching the video of the robot in action may be a bit underwhelming, but even moving fractions of an inch it's still doing something important, the researchers claim.
As one example, Rocklin said that the research done by his team relates to studies into "impossible engines," like the experimental EmDrive.
First proposed in 2006, the EmDrive uses microwaves in a vacuum chamber to theoretically create thrust by bouncing against a surface. Tests performed at TU Dresden found that thrust reported in initial EmDrive experiments was due to the test unit's interaction with Earth's gravitational field, and didn't indicate the device would actually work.
Rocklin told The Register that the EmDrive would "seriously break physics" were it to work, as there would be no way for it to gain momentum, something that his curved-space robot overcomes.
Curved space could theoretically get the EmDrive moving, Rocklin said, but at far too small a degree to be experimentally detectable. "To see movement via this effect you'd need far greater curvature, such as that present in the vicinity of a black hole," Rocklin told us.
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To explain the similarity, the researchers pointed to GPS systems, which rely on slight gravity-induced frequency shifts to report locations to satellites. "While the effects are small, as robotics becomes increasingly precise, understanding this curvature-induced effect may be of practical importance," Georgia Tech said.
Rocklin's shuffling robot may not move far, but the curved bit of "space time" it operates on isn't that curved. Like looking at the ocean horizon, it's pretty difficult to see the curvature of the Earth when viewed from up close.
Apply those principles to black holes, where space is theoretically curved more than anywhere else in the known cosmos, and the system could become practical.
"Ultimately, the principles of how a space's curvature can be harnessed for locomotion may allow spacecraft to navigate the highly curved space around a black hole," Georgia Tech said. With the nearest suspected black hole sitting over 3,000 light years from Earth, it'll be a while before we can test that. ®