The astronauts would have to propel their body to safety, kicking and waving their limbs, if they became stranded in the void of space.
They are left to float without hope for the rest of their lives. Their flailing might not be so bad if the Universe was curved.
The explanation of why things moved was given centuries before we left the Earth. Whether it's the expulsion of gas, a shove against solid ground, or the swish of a fin against a fluid, the result is a reaction that drives an object forward.
Take away the air surrounding a bird's wing or the water around a fish's tail and the effort of each flap will push one way as it pulls the other, leaving the poor animal to flutter Feebly without any net movement towards its destination.
Physicists thought of a loophole to the rule early in the 21st century. If a 3D space in which this movement occurs is curved, changes in an object's shape or position won't necessarily follow the usual rules on how momentum is exchanged.
A subtle net change in an object's position is possible because of the geometry of curved spacetime.
On the other hand, the idea that spacetime has an effect on motion is as obvious as a rock falling to the ground. It was covered in Einstein's general theory of relativity.
It's important to show how the rolling hills and valleys of distorted space might affect an object's ability to self-pilot.
A 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 to observe this in action.
Their mechanical version of a spherical space consisted of a set of mass driven by actuated motor. The setup was attached to a rotating arm and placed in a way that the pull of gravity and drag would be minimal.
The system was balanced so that the bend in the tracks would have the same effect as a curved space. The team thought so.
As the robot moved, the mix of gravity, friction, and curve combined into a movement that was best explained by the geometry of the space.
"We let our shape-changing object move on the simplest curved space, a sphere, to systematically study the motion in curved space."
As the robot changed its shape, it inched forward around the sphere in a way that could not be attributed to environmental interactions.
As small as the effect was, using these experimental results in line with theory could help improve the positioning of technology in localities where the universe's curve becomes important. Understanding how contained movements might affect ultra-precise positioning in the long term is more important than ever.
Physicists have been on the path of zero-propellant engines before. There is no end to debate over the validity of the theories behind small hypothetical forces in experiments.
The effects of swimming over the Universe's sharp edges could be revealed with further studies.
We can only hope that the gentle slope of the void surrounding our poor astronauts will allow them to find a safe haven before they run out of oxygen.
The research was published in a journal.
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