Unpopular Science
Sidenote illustration by Jess DG Hayes for chapter 14, “A Circle of Time”
Sidenote illustration by Jess DG Hayes

Chapter 14 of 50

A Circle of Time

“Time is an illusion. Lunchtime doubly so.”
Douglas Adams, 1979
“I’m not a creative type like youwith your work sneakers and your left-handedness.”
Jack Donaghy, 2008

In a cylindrical universe with compact spatial dimensions, twins can separate and reunite without acceleration, with one traveling around the circumference while the other remains stationary. Despite neither experiencing acceleration, they age differently upon reunion, creating a variant of the famous special relativistic paradox. In non-orientable topologies such as the Klein bottle universes, travelers can additionally experience reversal of chirality. Even a thoroughly non-dextrocardic explorer might come back from a cosmic stroll with his heart on the right side, no trauma needed.

Topics

  • Twin Paradox
  • Special Relativity Postulates
  • Proper Time Paths
  • Compact Space Topology
  • Cylindrical Universe
  • Acceleration-Free Paradox
  • Preferred Frame Detection
  • Klein Bottle Spacetime
  • Chirality Reversal
  • CMB Topology Search
  • Flatness Constraint

Sidenote

Top (Twin Paradox Variants): Variants of the twin paradox. The first shows the standard scenario: one twin remains on Earth while the other travels to a distant star and back at relativistic speed, experiencing less proper time due to time dilation and the non-inertial turnaround. The second panel sets the paradox in a compactified spacetime, where space is wrapped into a cylinder. Here, a twin can traverse the compact dimension at constant velocity — never accelerating or changing frames — yet still accumulate less proper time than the twin who remains stationary. Bottom (Non-Orientable Topology): Non-Orientable topology and global spacetime orientation. Depicted as a Möbius-like strip, this represents a spacetime where following a continuous timelike path can bring a traveler back to their starting point with their internal orientation flipped.

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Beyond Popular Science: the films

Each chapter is becoming a short film: the book’s own words, read to camera, with its figures, sources and equations animated alongside.

The films go out under the UK edition’s title, Beyond Popular Science. The fifty chapters are the same in both editions.

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Front cover of Unpopular Science by David H. Silver: hand-drawn science doodles by Jess DG Hayes around the title

This chapter is one of fifty in Unpopular Science.

For readers curious enough to want the actual mathematics, tired of science communication that oversimplifies or sensationalizes. Science as it actually is: demanding, complex, but well worth the effort.