Vertical curved track on swivel arm

Robot shows it’s possible to swim in a curved universe

If an astronaut were suddenly adrift in the void of interstellar space, they would be forced to push their bodies to safety, kicking and waving their limbs toward the sanctuary in the vacuum.

Sadly for them, physics isn’t so forgiving, leaving them afloat without everlasting hope. If the universe is curved enough, their waving might not be so futile.

Centuries before we left the Earth’s tugboat, Isaac Newton succinctly explained why things move. Whether it’s an expulsion of gas, a push against a solid ground, or the swish of a fin against a fluid, the momentum of the action is conserved by the sum of the elements involved, resulting in a response that propels the object forward.

Take away the air around a bird’s wings or the water around a fish’s tail, and the force of each flap will push in the same way when pulling in the other direction, leaving the poor animal flapping feebly without any net motion to its destination .

In the early 2000s, physicists saw a loophole in the rule. If the 3D space in which this motion occurs is curved, the change in the object’s shape or position doesn’t necessarily follow the usual rules about how to exchange momentum, which means it doesn’t require propellant.

Bending the geometry of spacetime itself could mean a deformation of an object—the right kick, flap, or quiver—after all, there could be subtle net changes in its position.

On the one hand, the idea that the curvature of spacetime has an effect on motion is as obvious as watching a stone fall to the ground. Einstein already covered this in his general theory of relativity more than a century ago.

But showing how the rolling hills and valleys of warped space affect the object’s own ability to propel itself is another story.

To observe this phenomenon without traveling to the nearest space-warping black hole, a team of researchers from Georgia Tech, Cornell University, the University of Michigan and the University of Notre Dame built a curved space model in the lab.

The mechanical version of their spherical space consists of a set of masses driven by drive motors along an arched orbital intersection. Attached to the swivel arm, the entire unit is positioned in such a way that gravity and frictional drag are minimised.

A “space” swimmer travels on the orbit of a rotating arm. (Georgia Tech)

While mass isn’t separated from the physics that govern our slightly flat universe, the system is in equilibrium, so curvature in orbits can cause the same effects as space that’s visibly curved. Or as the team predicted.

As the robot moves, a mix of gravity, friction, and curvature combine into a motion with unique properties that are best explained by the geometry of space.

“We have our deformable objects move over the simplest curved space (a sphere) to systematically study motion in curved space,” said Georgia Tech physicist Zeb Rocklin.

“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.”

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Although the effects are small, theoretically using these experimental results could help improve the positioning of technology where the curvature of the universe becomes important. Even in a gentle descent like Earth’s own gravity well, understanding how the motions involved alter ultra-precise positioning may become increasingly important in the long run.

Of course, physicists have gone down the road of zero-propellant “impossible engines” before. Small hypothetical forces in experiments have a way of coming and going, generating endless debate about the validity of the theory behind them.

Further research with more precise machines could reveal more insights into the complex effects of swimming on the sharp edges of the universe.

For now, we can only hope that the gentle slope of the void around our poor astronauts is enough to see it reach a safe haven before their oxygen runs out.

The study was published in NASA.

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