If an astronaut were suddenly adrift in the vacuum of interstellar space, they would be forced to propel their body to safety, kicking and flailing their limbs toward a void sanctuary.
Unfortunately for them, physics is not so forgiving, leaving them to float hopelessly into eternity. If the Universe were curved enough, its turmoil might not be so pointless.
Centuries before we left the pull of the Earth, Isaac Newton succinctly explained why things moved. Whether it’s the expulsion of gas, a push against solid ground, or the snapping of a fin against a fluid, the momentum of an action is conserved by the sum of the elements involved, resulting in a reaction that propels an object forward. .
Take away the air around a bird’s wing or the water around a fish’s tail and the effort of each fin will push equally one way and the other, leaving the poor animal fluttering feebly with no net movement towards its destination. .
At the beginning of the 21st century, considerate physicists a way around this rule. If a 3D space in which this motion occurs is curved, changes to an object’s shape or position won’t necessarily follow the usual rules for how momentum is exchanged, meaning you wouldn’t need a thruster.
The geometry of curved spacetime itself could mean deforming an object (the right kick, flap, or flutter), and you could see a subtle net change in its position after all.
On the one hand, the idea that the curvature of space-time influences motion is as obvious as seeing a rock fall to the ground. Einstein covered it over a century ago in his general theory of relativity.
But showing how the rolling hills and valleys of warped space can affect an object’s ability to self-propel is another ballgame.
To observe this in action without traveling to the nearest space warp black holeA team of researchers from the Georgia Institute of Technology, Cornell University, the University of Michigan and the University of Notre Dame built a model of curved space in the lab.
His mechanical version of a spherical space consisted of an array of motor-driven masses driven along a crossroads of arched paths. Attached to a rotating arm, the entire setup was positioned so that the pull of gravity and drag from friction were minimal.
- A motorized ‘space’ swimmer on the track of a rotating arm. (Georgia Tech)
While the masses didn’t break away from the physics that dominate our somewhat flatter Universe, the system balanced itself so that the curve in the tracks induced the same sort of effect as a significantly curved space. Or so the team predicted.
As the robot moved, the combination of gravity, friction, and curvature combined into a motion with unique properties best explained by the geometry of space.
“We let our shape-changing object move in the simplest curved space, a sphere, to systematically study motion in curved space.” He says Georgia Tech physicist Zeb Rocklin.
“We learned that the predicted effect, which was so counterintuitive that some physicists ruled it out, did in fact occur: as the robot changed shape, it inched around the sphere in a way that could not be attributed to environmental interactions.
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However small the effect, using these experimental results in line with theory could help improve the positioning of the technology in locations where the curvature of the Universe becomes important. Even in gentle dips like Earth’s gravity well, understanding how contained motions can upset long-term ultra-precise positioning could become increasingly important.
Physicists have, of course, gone down the path of zero propellant.impossible engines‘ prior to. Small hypothetical forces in experiments have a way of coming and going, generating endless debate about the validity of the theories behind them.
Further studies with more precise machinery could reveal more information about the complex effects of swimming over the sharp edges of the Universe.
For now, we can only hope that the gentle slope of the void surrounding our poor astronaut is enough to see him make it to a safe haven before his oxygen runs out.
This research was published in PNAS.
