Reality → Base → Physics → Key concepts
Electromagnetic waves. Electromagnetic radiation is usually described by the wave model, preponderantly for the non-ionizing part of the electromagnetic spectrum. The waves propagate at the speed of light and consist of oscillations in the mysterious electromagnetic field with an electric and a magnetic component. The field, itself devoid of any matter, permeates the vacuum. While the existence of invisible static electric and magnetic fields can be vividly demonstrated by simple experiments, complex mathematics and ingenious tests led to the discovery of the hidden and inscrutable electromagnetic field, which now is being exploited with incredible precision for wireless data transmission.
Photon. The quantum mechanical model of electromagnetic radiation is based on the concept of wave-particle duality. It elucidates phenomena that cannot be understood with the wave model, such as the photoelectric and Compton effects. The photon's particle concept has been most successful in advancing laser science, photonics, and high-energy physics. In theoretical physics, the quantum field theory treats photons as exited states of a quantized electromagnetic field, or as minuscule wave packets.
Relativity. Einstein's theory of general relativity 'explains' the familiar yet mysterious gravitational force but is not reconcilable with quantum mechanics and the related Standard Model. For now, general relativity and quantum mechanics provide the most fundamental explanation of the physical world, but the search for new discoveries and an eventual theory of everything continues.