Electromagnetism
What's more, Maxwell's studies showed that light could be described as a ripple in the electromagnetic field. That is, light moves like a wave. However, Maxwell's work did not agree with classical mechanics, the description of forces and motion originally developed by Newton. Maxwell's equations predicted that light always moves through empty space at the same speed. This was a problem because in classical mechanics, velocities are "additive"-- if a person A on a train moving at speed X throws a ball with speed Y, then a person B on the ground sees the ball moving with speed X+Y. According to Maxwell, if person A turns on a flashlight, they will see the light moving away from them at speed c. But person B on the ground must also see the light moving at speed c, not c+X. This led to the development of the theory of special relativity by Einstein, which explained how the speed of light could be the same for everyone, and why classical mechanics does not work for things moving very fast.