"as big as a universe"?
Japanese is a very contextual language.
For example,
宇宙 has three different meanings; "universe", "cosmos", and "outer space", all of which are used in varying measures depending entirely on text; like how 星 can mean "star" or "planet" (
Lord Boros, anybody?). In the context of the episode summary, "universe" is completely and utterly erroneous. Again, not a
single line of dialogue is ever spared to
mention the universe or compare the Anomalous Space to the universe, for that matter. Previous context in the text, that being
"The battle spreads to outer space", lends itself to 宇宙 referring to "outer space", rather than "universe".
Y'know the funniest part?
Guess what kanji is
machine translated into "outer space" and what kanji is translated into "universe".
The answer is 宇宙. For the two of 'em.
How weird that the only two instances of 宇宙 are translated differently
by the machine.
How weird that
Japanese astronomers refer to 宇宙 as "a [representation] of the expanse of space", denouncing its relation to the dimension of time.
"an extra dimensional space in this context"?
異次元空間, or "different dimensional space", not a separate space-time, not an "extra-dimensional space".
For comparison, "extra-dimensional" is
超次元; "higher-dimensional" is
高次元.
異 is "different"; 高 is "higher"; 超 is "super"/"extra".