The Big Rip

There is some evidence that the Manifold Sky is expanding outwards in all dimensions at once. For example, tension experiments at the Sky Lattice over Petalcap Vale show that, although it is occuring over geological time, the inflection layers are expanding, assuming that this phenomena cannot be explained for unaccounted for sagging. Similarly, geophysical circumvection is believed to drive an expansion of landmasses, but the commissures somehow have remained open - or even grown in some small measure - over the course of recorded history despite in-falls from erosion or flooding.
This evidence has caused some to speculate that, the forces driving the expansion of the Manifold Sky might drive the habitable landmasses apart, push the inflection layers higher and wider, and expand the commissures. Eventually, life in the cubes and travel across tesseracts might become untenable due to the extreme distances involved. The rising height of the inflection layers would eventually mean that the air there would be too thin to permit travel by airship, requiring the development of rocket technology before eventually perhaps even foreclosing this option. Millions of years in the distant future, perhaps even the very fabric of space might rupture, exposing the once-Manifold's interior to the unseen Celestial Realms beyond. This distant cosmological event is colloquially known as "The Big Rip."

Historical Basis

Because the rate and acceleration of expansion are unknown due to the limited sensitivity of instruments as of 10,000 AR, is remains unknown if a Big Rip scenario is any more likely than other physical apocalypses which might befall the Manifold before then. Certainly, organizations like the Manifold Conservation Society and the Navigator's Guild regard more immediate concerns, such as the ongoing War of Reunification and proliferation of Distal Tesseract species into adjacent tesseracts as being more likely to cause the extinction of sentience long before any such cosmological disaster. Still, the mythology of The Curved Time persists into the present day, so there is always remains the possiblity that a heretofore paradigm shift could cause upheavals on a similar scale.