What is the universe expanding into?

I know this question is more about physics than philosophy, but I do wonder.

There is strong scientific evidence to show that the universe is expanding, and for the most part, I agree with that evidence.

But I wonder if it makes any sense to ask (and I cannot help myself): what is the universe expanding into?

Has anyone ever written anything on this, or does anyone have some personal ideas about it they would like to share? Thanks.

It’s expanding ‘into’ nothing or something non universal.

One we can already comprehend the other as far as i know we can’t, unless we can make it to the end of the universe and/or escape to find out what’s going on.

It’s thats simple, even simpler actually. ^^

It’s expanding into the unknown.

it’s not expanding, it’s running away…

-Imp

It is expanding into other universes.

These exchange matter and information.

When a critical mass of universes collide, they explode again outward, creating new universes.

There is something bigger than the universes … and it is learning itself.

It’s conceptually impossible for us to “zoom out” to the “expanding boundary” of the universe. The question therefore has no answer.