Hi all, I have a question about the formulation of quantum field theories in curved spacetime. I'm still learning, and so I might not articulate this very well, but I'm wondering: If a region of spacetime can warp and curve, dynamically changing its shape in response to changes in energy density, then I assume a quantum field defined over the same region would also have to expand / contract? Can the field be thought of as something 'physical', and if so, in the case of expansion, where does the extra 'quantity' of field (for lack of a better description) come from? Or is it better to think of the field as being 'stretched' and 'compressed'? Thanks all.