Photons, the fundamental particles of light, are massless entities that travel at the speed of light in a vacuum. Once created, a photon is characterized by its energy, which remains unchanged until the photon is destroyed. Photons, unlike electrons, do not interact with each other; they cannot exchange energy or momentum. When a single photon is incident upon a beamsplitter, its wavefunction is spatially separated into two parts, corresponding to reflection and transmission. However, a photon is an indivisible elementary particle. When a measurement is made, the entire photon will be detected either as 100% transmitted or 100% reflected. In the time and space interval between the beamsplitter and the detector, the photon is delocalized.
Photons can be absorbed by nuclei, atoms, or molecules, provoking transitions between their energy levels. A classic example is the molecular transition of retinal, which is responsible for vision. The absorption provokes a cis–trans isomerization that, in combination with other such transitions, is transduced into nerve impulses. The absorption of photons can even break chemical bonds, as in the photodissociation of chlorine; this is the subject of photochemistry.
In summary, photons are fundamental particles that exhibit both wave-like and particle-like properties. They travel at the speed of light and can interact with matter in various ways, including absorption and emission, leading to phenomena such as vision and photochemistry. Their behavior is governed by the principles of quantum mechanics, which describe their interactions and transformations over time.
Categories: Quantum physics