Much ink has been spilled by many a philosopher on the topic of whether or not numbers "magically exist." Plato was the obvious example of a philosopher who believed numbers "exist" independent of our universe. Though no one is saying they exist "in the physical universe", but it's not a given that they cna't possibly exist if not "within our universe."

Think of it this way. Graham's number is an absolutely enormous number, right? Let's assume for the sake of argument that nobody has ever computed the Graham's-number-th digit of pi. We know for certain that there is a Graham's-number-th digit of pi. And we know that if two people calculated it independently, they'd get the same digit. But (at least in this hypothetical) nobody has actually ever done the calculation to see what the Graham's-number-th digit of pi is. Given all I've said so far, the act of finding out the Graham's-number-th digit of pi seems more like an act of discovery of something that already existed than an act of invention of something that didn't already exist. So, it seems quite reasonable to many to conclude that numbers "exist."

Also, Iah's view does imply that our universe does not encompass all of existence. It also implies that no calculation device need exist anywhere.