The universe is expanding. It then seems logical to say that the QM fields are expanding as the universe expands. My question is how does this happen? When I consider an expanding field it forces me to consider the actual properties of the field. Are the QM fields becoming less dense or are these fields only mathematical constructs that enable predicts to be made. If the fields are not only mathematical then does their expansion require the creation of new field “stuff” to fill in the new space being created. QM mathematics is way out of my skill level so an answer that respects my curiosity and understands my limitations is appreciated.
Photons are quantum particles you get when the electromagnetic field is quantized. So consider the photons which make up the cosmic background radiation. They were generated when the mean temperature was about 3,000 K, but now represent a temperature of about 2.7 K. They didn't "cool off", but instead their wavelengths increased with the cosmic expansion, which can be easily calculated as 1100 = 3,000 K/ 2.7 K, which is the expansion since the cosmos cooled below the hydrogen ionization level.
No fancy math is required, just experimental results.