Quantum fields carry a certain amount of energy, even in seemingly empty space, and the amount of energy gets bigger as the fields get bigger.
Different quantum fields gives rise to electrons, the Higgs boson, and all the other fundamental objects in the Standard Model of particle (or should it be wave?) physics.
The particular, eternally persisting, elementary physical stuff of the world, according to the standard presentations of relativistic quantum field theories, consists (unsurprisingly) of relativistic quantum fields.
Go big enough, and the amount of energy in the quantum fields becomes so great that it creates a black hole that causes the universe to fold in on itself.
The quantum fields through which quarks and leptons interact with each other and with themselves consist of particle-like objects called quanta (from which quantum mechanics derives its name).
What is being questioned is whether this means that gravity cannot itself remain fundamentally classical while interacting with quantum fields.
