When I read about the expanding universe and inflation I often see pictures like this:
(Source: https://en.wikipedia.org/wiki/Inflation_(cosmology))
or explanation like this:
For getting an idea of space expansion you have to imagine a cubic grid throughout the whole space where the grid/ the number of cubes does not change, but each cube is increasing in size. It is similar to a sort of "stretching" of the size of the cubes.
(Source: Expanding universe - Creation of Space)
My question is this: These descriptions only make sense if you assume a space around the universe which serves a frame of reference for measuring the expansion. In the picture from Wikipedia the expansion takes place with reference to the black background of the image. In the example with the expanding grid there has to be some kind of meta space around the cubes to have a frame of reference for measuring the expansion. An observer within the cubes cannot measure the expansion, as his frame of reference grows at the same time.
To my knowledge at the Big Bang both space and time have been created, so in my understanding there is no meta space which could be used as a frame of reference to measure inflation or an expanding universe.
How can I reconcile the concepts of an expanding universe / inflation without having to assme a meta space within which this expansion takes place?
FYI: I'm not a physicist, so please bear with me if this a noobie question.
