Photons, despite being massless particles, can indeed interact with matter. This is because interactions between photons and matter are governed by the electromagnetic force, which does not depend on the mass of the particles involved.
The electromagnetic force arises from the interaction between electrically charged particles, such as electrons and protons. Photons, as the carriers of the electromagnetic force, mediate the interaction between charged particles. When a photon encounters charged particles within matter, several different processes can occur:
Absorption: A photon can be absorbed by an atom or molecule, transferring its energy to the system. This can cause an electron to be excited to a higher energy state or can even lead to ionization, where an electron is completely removed from the atom.
Emission: An excited atom or molecule can release a photon when an electron transitions from a higher energy state to a lower one. This is how light is emitted, for example, when an electron returns to its ground state after being excited.
Scattering: Photons can also scatter off charged particles without being absorbed. Elastic scattering involves a change in direction and energy of the photon, while inelastic scattering involves energy transfer between the photon and the charged particle.
These interactions occur due to the electric charge of the particles involved, and the mass of the photon does not play a direct role. It's important to note that while photons themselves are massless, they can still carry energy, momentum, and angular momentum, allowing them to interact with matter.