 We saw in our first segment the particles with electric charge create an electromagnetic field around themselves that stretches out in all directions. This field is attached to the particle. It will go where the particle goes. In quantum field theory, fields like these are quantized. That is, they contain tiny massless, energyless bits of the field. We have seen that the photon is a certain type of disturbance. An excitation, or vibration, in the electromagnetic field will call these a localized, vibrating ripple. It moves with a life of its own. It is not attached to the particle that created and sustains the field. The photon has no mass, no charge, a spin of one, making it a boson, and travels at the speed of light in a vacuum. In our segment on the atom, we saw that energy was quantized and equal to Planck's constant times the photon's frequency.