Abstract
Whenever an experiment can be described classically, quantum physics must predict the same outcome. Intuitively, there is nothing quantum about an accelerating observer travelling through a vacuum. It is therefore not surprising that many people are puzzled by the Unruh effect, which predicts that the observer encounters photons in a thermal state. This paper employs locality and spatial and time translational symmetries to demonstrate that the assumption of a common vacuum of the quantized electromagnetic field in all inertial and non-inertial reference frames is consistent with the principles of special relativity. A key difference between a resting and an accelerating observer is that they each experience a different zero-point energy density.