Quote Originally Posted by danzibr View Post
Void inside the (observable) universe has properties, like permittivity and permeability of free space. Question is, would the same hold for outside? Would there be a way to know?
Well, that's kind of the definition of outside the observable universe: the observable universe ends where you stop being able to know those things.

The prevailing philosophy (Copernican principle) is that we should assume what we can see typical. This is not to say identical, for example there was a famous statistic that the typical family had 2.4 children, but obvious no actual family has 2.4 children; the number varies and you should expect it to find variable numbers of children as you see new, normal families.

So going back to permittivity and permeability of free space. Do these numbers vary ever, even in the slightest? Our understanding is no, so we expect the unobservable universe to have these same values.