Light with longer wavelengths travels faster in glass compared to light with shorter wavelengths due to differences in how they interact with the material's atomic structure. This phenomenon is linked to the concept of diffraction, where shorter wavelengths experience more scattering and thus slower propagation. The discussion references Richard Feynman's lectures on Quantum Electrodynamics (QED) for deeper insights into these principles. Understanding the underlying physics requires exploring the relationship between wavelength, speed, and material properties. These concepts are crucial for grasping the behavior of light in various mediums.