[bk1000]

"... every day, our cosmos grows bigger and bigger,..."

Expanding into what? That just sounds silly. Is the cosmos minuscule compared to the emptiness it has not yet expanded into?

[Telepathic Intruder]

"Expanding into what?"

The standard model of the Big Bang says the universe doesn't have an outside, and is expanding relative to itself only. But there are other theories (hypotheses really), such as "brane cosmology" claiming there are higher dimensions embedding our own universe. But since we are only able to see a finite part of our universe limited by the visible horizon which is expanding away at c, it could be any size. Brian Greene wrote in "The Fabric of the Cosmos" that if inflation theory is correct, the actual universe is at least 10⁴⁰ times larger than the visual one (the visual one being about 93 billion light years across). Maybe even 10¹⁰⁰ times larger or more.

[Taipei]

It’s not expanding into anything, space itself is expanding.