reflections

Reflections are the return of waves or particles after striking a boundary between media. In everyday language, reflection also denotes careful consideration of one's thoughts, feelings, or experiences.

In optics, the law of reflection states that the angle of incidence equals the angle of reflection, measured from the surface normal. A smooth boundary yields specular reflection, producing clear images, while a rough surface leads to diffuse reflection, scattering light in many directions. Total internal reflection occurs when light moves from a denser to a rarer medium and the incidence angle exceeds a critical value, preventing transmission and causing light to be trapped inside the original medium.

In geometry, a reflection is a symmetry operation that maps every point to a mirrored position across a line (2D) or a plane (3D). Reflections are isometries and form the basis of reflectional symmetry in figures.

In acoustics, reflected sound waves affect room acoustics and reverberation. In computing, reflection refers to mechanisms that allow a program to inspect and interact with its own structure and metadata at run time. Reflections influence technologies from mirrors and periscopes to imaging systems and various theoretical frameworks in science and philosophy.