The Most Sensitive Experiment Is the Sun's Magnetic Field

The best description of the universe that we see around us is one where light has no mass. We have definitely tried to measure the mass of light and every experiment is consistent with light having no mass. If light had a lot of mass, it would be obvious. It would look very different. Things would travel faster than it. So by looking at the sun's magnetic field, we can tell that light, if it has any mass, it's an incredibly small value.