Like a lot of language we use when discussing things at the universe scale, the word “expanding” operates as a placeholder with analogs in day to day life but isn’t a perfect representation of what we mean.
The “universe” itself is space and time. When we say “expanding” we simple mean that galaxies are observed to be moving farther away from each other. That does not at all imply some kind of “expansion into another space” - space itself is exhibiting this property and we are observing it. That’s all.
The “balloon” analogy and the usage of the word “expand” in this context are both imperfect metaphors for physical phenomena we are observing.
It is a bit like trying to discuss what happened “before” the Big Bang - there is no “before” - time was created.
There are many phrases you can construct which may seem like they “make sense” but are actually combining a set of word concepts in ways that are self-contradictory.
The “universe” itself is space and time. When we say “expanding” we simple mean that galaxies are observed to be moving farther away from each other. That does not at all imply some kind of “expansion into another space” - space itself is exhibiting this property and we are observing it. That’s all.
The “balloon” analogy and the usage of the word “expand” in this context are both imperfect metaphors for physical phenomena we are observing.
It is a bit like trying to discuss what happened “before” the Big Bang - there is no “before” - time was created.
There are many phrases you can construct which may seem like they “make sense” but are actually combining a set of word concepts in ways that are self-contradictory.
“What is space expanding into?”
“What happened before time was created?”
Etc.