I'll just leave something I wrote for a cosmology page that never came to fruition, but I saved the explanation to avoid having to write it again.
"I believe the official English translation should be used as support. The phrase "
endless expanse" does not imply something that is constantly expanding.
An
expanse typically refers to a vast stretch of something, such as the sea, sky, or land. For example, "a vast expanse of grassland" means a large, open area of grass. Synonyms for expanse include
area, range, field, and
space. Therefore, "
endless expanse" does not mean an
endless expansion but rather an
infinitely large space.
Applying this to the Garganta, it suggests that the Garganta is an infinite space rather than something that is growing or expanding. This is further supported by the idea that the Garganta is so immense that the World of the Living (WoL) and Soul Society (SS) could be
compared to planets within it."