A plane wave traveling in the x-direction can be explained using Huygens' principle, where each point on the wavefront acts as a source of secondary wavelets. The confusion arises from the assumption that these wavelets would create a spherical wavefront, but the key is that the wavefront consists of all wavelets acting together. This collective behavior maintains the plane wavefront rather than transforming it into a spherical shape. Understanding that all points contribute simultaneously clarifies the concept. The discussion emphasizes the importance of recognizing the collective nature of wavelets in maintaining the integrity of the plane wavefront.
