We are told that Expansion of Space is the result or derivation or “prediction” of FLRW metric.
Second component of FLRW metric “L” stands for Lemaitre. So let us first see what did he say and what that thing became in FLRW metric.
This thing centers around equation No.23 of Lemaitre’s 1927 (French) Paper and 1931 Translation thereof. Following is relevant screenshot from my book (2018) where I have explained it.
And following is PDF link of the relevant section of book:
Georges Lemaître and Expanding Universe - Book: “A Philosophical Rejection of The Big Bang Theory”
So Lemaitre was only talking about “expansion of radius of whole universe” and this thing was made out into literal “expansion of space” by the FLRW metric.
And this is the example of so-called “rigorous mathematics” of the official Cosmology.
Now we can talk about “F” (Friedmann), the first component of “FLRW metric”.
Friedmann did talk about Radius ‘R’ of Universe in terms of Expansion and even Contraction.
But his meaning of ‘R’ was “Curvature of Space”. So basically he also did not talk about expansion of space in the sense of FLRW metric. Following is screenshot from my book (2018) where I explained this thing.
“R” and “W” … they are not important because they only modified “F” and “L” at a time when Hubble Law was already surfaced.
Following is PDF link to relevant section of book:
Alexander Friedmann and Expanding Universe - Book: “A Philosophical Rejection of The Big Bang Theory”