No scientific theory is absolutely correct and unchangeable. Any scientific theory is the product of human's periodic cognition, which will continue to be improved with the development of new discoveries and scientific technology. It has been found that the electric field can be generated by the friction, and the changing electric field can be generated by constant friction. After the friction stops, the electric field called electrostatic field will exist for a period of time or even longer. Accordingly, a series of experiments were designed. The 1-watt bulb can be lighted by collecting the changing electric field energy when a polymethyl methacrylate (PMMA) board was rubbed with polytetrafluoroethylene (PTFE) film by hand. When a closed coil was placed in the generated changing electric field, an induced current and an induced electromotive force were generated in the coil, and the scissors in the coil can be magnetized. The 1-watt bulb can be lighted by the generated changing electric field, when one end of the plastic rod was rubbed by fur. Besides, the magnetic phenomenon was produced in the closed coil connected to the plastic rod. In addition, we found that shaking the plastic rod with an electrostatic field generated by the friction can also generate a changing electric field, which not only wirelessly lighted the 28-watt fluorescent tube lamp, but also produced an induced current and an induced electromotive force in the closed coil nearby the lamp. Based on the above experiments, we have the following speculation. Just as the unified theory of electromagnetism, the changing electric field produces a magnetic field, and the varying magnetic field produces an electric field. In fact, the electric field is a magnetic field and the magnetic field is an electric field, so they can be regarded as energy fields in essence. The coil and conductor can be regarded as the energy collector that can collect energy from the energy field, as long as there is a relatively constantly changing energy field in the collector. The conduction current is transmitted in the collector, while part of the energy field that is not collected in free space, which corresponds to the displacement current in the fourth equation of Maxwell's equations. The essence of Maxwell's equations and related laws are two different phenomena resulting from energy field in the closed-loop self-circulating state or open-loop acyclic state (truncated to < 400 words by viXra Admin).