Structure
The tube is a distortion of spacetime that can be intentionally created (using hypothetical technology) in the wake of travel near the speed of light. The Krasnikov Tube allows for a return trip that takes you back to the time right after you left. This several light-year long man-shaped "tube" might arguably constitute a megastructure, but unlike most megastructures it's not constructed of physical matter such as titanium or plastic, but instead is just a distortion of spacetime.
Experiencing the effect requires that the traveler race along the tube at speeds close to that of light.
Read more about this topic: Krasnikov Tube
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