Yes, scientists have indeed concluded that light exhibits wave-particle duality. Light can behave both as a wave and as a particle called a photon. This concept is a fundamental principle of quantum mechanics.
The wave-like nature of light was initially established through various experiments, such as the famous double-slit experiment, which demonstrated interference and diffraction patterns characteristic of waves. These experiments provided evidence that light exhibits wave-like properties such as interference and diffraction.
However, the particle-like nature of light was revealed through the observation of certain phenomena that couldn't be explained purely by wave behavior. For example, the photoelectric effect, where light can cause the ejection of electrons from a material, demonstrated that light energy is quantized into discrete packets of energy called photons. These experiments showed that light can also behave as discrete particles.
Regarding the masslessness of photons, it is true that photons are considered to be massless particles according to the Standard Model of particle physics. They do not possess rest mass, meaning they always travel at the speed of light in a vacuum. Despite their lack of rest mass, photons carry energy, momentum, and exhibit wave-like behavior.
The wave-particle duality of light can be quite perplexing, but it is a fundamental aspect of quantum mechanics. It highlights the complex and fascinating nature of light and the microscopic world in which it operates.