If you observe 'expanding space' somewhere far from you (receiding galaxies obeying Hubble's Law), it has something to do with your local clock and ruler here on Earth.
It has something to do with the difference between your clock and the hypothetical clocks in intergalactic space over there.
If you observe curved space far away from you, due to gravity, the amount of observed curvature somewhere else has something to do with your local idea of a straight line. Determined by your local clock in your own curved spacetime environement.
Wherever you are in curved spacetime, your local idea of a straight line and your local clock determines what you will observe somewhere else about space being curved or expanded.
Every observer has his/her own ruler or clock. He or she or it is the measure for space and time somewhere else (through a telescope far from the observer's location).
ps: I do not believe in the Big Bang theory. I think that 'the observed expansion of space' has something to do with our local clock. (our local idea of time). Whatever we observe to be going on with space elsewhere (curvature or expanding space), it has something to do with our local idea of time and the clocks over there. Because time and space are related.
Maarten Vergucht
Philosopher of time and space.