According to current scientific understanding, particles of light, known as photons, are considered to be massless. Photons are elementary particles and the carriers of electromagnetic radiation, including visible light. They are described by the theory of quantum electrodynamics (QED), which treats them as massless particles.
The masslessness of photons is supported by various experimental observations and theoretical frameworks. For example, the behavior of light in experiments, such as the double-slit experiment and the study of electromagnetic waves, is consistent with the properties of massless particles. Additionally, the Standard Model of particle physics, which successfully describes the known elementary particles and their interactions, treats photons as massless.
However, it's important to note that there are theoretical extensions to the Standard Model, such as certain quantum gravity theories, that suggest the possibility of photons having a tiny nonzero mass. These proposals arise in attempts to reconcile quantum mechanics with gravity and address some cosmological puzzles. However, the evidence for the existence of a nonzero mass for photons is currently lacking, and experimental observations continue to support their masslessness.
In summary, based on our current understanding and experimental evidence, photons are considered to be massless particles. However, it is always possible for scientific theories and understanding to evolve as new evidence and insights emerge.