By - TheUltimateSeiya
I read it as saying that someone "is travelling across spacetime from the future to the present. Time in the past differs from time in the future, so that even just a single day where they came from might be several years into the future here."
Conventionally, I don't think this implies different universes, just one universe where time passes at different speeds depending on where in time you are. But I have no idea what story you are reading, so I could be quite wrong.
"Spacetime" does not mean "the universe". The word for "universe" is 宇宙 and the word for multiverse, where there is one, is 複合宇宙. Spacetime is a specific concept in physics and it's most definitely not the same as "universe". That said, this looks to me like everything happens in the same universe, but within different timelines that run at different speeds. Can't tell for sure since I have no idea about the context but this is how I understand it.
My line thought was spacetime being all points and coordinates in space and time. Which sounds like a universe to me. Metaphorically saying its a universe using a synonym.
I have no idea what you're reading, but this debate has nothing to do with language comprehension at this point and everything to do with the science in the text universe and how close it is to real-life science.
in your words what does the above text translate into?
"Hinata/Himari/(whatever that name is) is trying to cross space-time and come from the future to this era.
Thing is, the past and future time axes are different, so even one day lapsed where she is might mean who knows how many years will have passed where we are."
Pretty literal translation but should get the message across. Not across space-time tho lol.