Imaginary part i is necessary when dealing with electromagnetic field. When i part=0 then energy is in physical reality and directly reachable to us. When i part=1 then energy is out of physical reality. We can call it imaginary reality but it is as real as the physical reality - today we just can't perceive it with physical senses/devices.

Dark matter/energy is probably energy in this imaginary reality. It influences us but we do not know how.

What is quanta? - It is minimum bit of energy oscillating between our reality and imaginary reality. Theoretically it is endless energy source as it is not possible to "empty" the quanta.

What is energy field? It is matrix of quantas. It is like a huge computer screen capable of expressing any 3D form - from sub atomic particles to planets, stars and galaxies.

What the matrix expresses? It is in big part defined by the "imaginary" reality...