Speed of light is constant because photon is massless. If this is wrong please correct me. So is it that any massless particle will move at speed of light? Do we know any such particles? There is this analogy that explains how particles get mass. Basically the higgs field gather around heavy particles and not around lighter particles. So when a photon moves there is no resistance from the higgs field and hence it moves fastest. But considering this analogy if another particle moves towards a photon with velocity u, speed of light will increase. What is wrong with this analogy? Is there any explanation why speed of light remains constant or is it just another fact, another one of those things that we have to accept?