Quantum mechanics provides an explanation for the transparency of materials to photons, as well as the reduction in the speed of photons when they pass through a medium. These phenomena can be understood in terms of the interaction of photons with the electrons and atoms within the material.
Transparency of materials to photons: In a transparent material, photons can pass through without being significantly absorbed or scattered by the atoms or electrons within the material. This behavior arises due to the energy levels and electronic structure of the atoms. When photons interact with the electrons in the material, they can be absorbed and then re-emitted. However, in a transparent material, the energy levels available for absorption and re-emission are such that the photons are typically re-emitted in the same direction and phase as the incident photons. This constructive interference between the incident and re-emitted photons allows the photons to pass through the material largely unimpeded.
Reduction in the speed of photons: When light passes through a material, such as a transparent medium, the speed of photons is slower compared to their speed in vacuum. This reduction in speed is a result of the interaction between the photons and the charged particles (electrons and atomic nuclei) in the material. As photons propagate through the material, they interact with the electric fields of the charged particles. These interactions cause the photons to undergo a series of absorption and re-emission processes, leading to a delay in their propagation. Effectively, the photons are scattered and redirected by the charges, which slows down their overall speed.
Energy state of individual photons: In a transparent material, individual photons do not change their energy state as they pass through. Photons themselves are quantum particles that carry energy proportional to their frequency. When a photon interacts with an atom or electron in the material, it may be absorbed and then re-emitted, but the energy of the photon remains the same. The change in the energy state of the material's electrons or atoms due to the absorption and re-emission processes is responsible for the slowdown and re-emission of the photons, but the energy of the individual photons remains constant.
It is important to note that the interaction of photons with materials is a complex quantum mechanical phenomenon. The behavior of photons in materials is described by the principles of quantum electrodynamics, which combines quantum mechanics with the theory of electromagnetism. The specific properties of a material, such as its electronic structure and the arrangement of its atoms, determine its transparency and the extent to which it affects the speed of photons passing through it.