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.

  • $\begingroup$ Philosophically an expanding universe either assumes the outer "meta-space" into which the contents of the universe are travelling and spilling out, or it attributes some sort of expansionary property to space itself (which doesn't involve the objects themselves moving). An alternative interpretation of the latter is that the scale of objects within the universe is contracting over time - like deflating balloons, the distance between the surfaces of objects grows, but the overall space taken up by the whole remains the same. All approaches really raise as many questions as they answer. $\endgroup$ – Steve Jun 3 '19 at 1:53
  • $\begingroup$ I'm not sure you'll get a answer that's useful to you, but essentially to reconcile these things you use mathematics. It makes sense in the language of mathematics used in general relativity (which is difficult), but it is at odds with people's common sense ideas of how things should work. You have to let go of the common sense ideas. I do not think you can reconcile the these abstract ideas with common sense. $\endgroup$ – StephenG Jun 3 '19 at 2:22
  • $\begingroup$ @StephenG I'm aware that the physical laws behind the statements are expressed in mathematical language. I'm not familiar with the mathematics behind it. Could you recommend a source (books, web page, video) which could help me address this problem? $\endgroup$ – WolfgangP Jun 3 '19 at 2:31
  • $\begingroup$ For SR, Spacetime Physics by Taylor and Wheeler. For GR, Ray D'Inverno's intro book is fantastic. $\endgroup$ – N. Steinle Jun 3 '19 at 2:40
  • $\begingroup$ We have questions and answers that list many books : see e.g. here. You might consider PBS Spacetime on YouTube for a video approach to concepts. Be aware that the mathematics can take a long time to learn. $\endgroup$ – StephenG Jun 3 '19 at 2:55