A
mirror image is a reflected duplication of an object that appears identical but reversed. As an
opticalOptics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
effect it results from
reflectionReflection is the change in direction of a wavefront at an interface between two differentmedia so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves...
off of substances such as a
mirrorA mirror is an object that reflects light or sound in a way that preserves much of its original quality prior to its contact with the mirror. Some mirrors also filter out some wavelengths, while preserving other wavelengths in the reflection...
or water. It is also a concept in
geometryGeometry arose as the field of knowledge dealing with spatial relationships. Geometry was one of the two fields of pre-modern mathematics, the other being the study of numbers ....
and can be used as a conceptualization process for 3-D structures. In
chemistryChemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
, a '"mirror image'" is a molecule having a spatial arrangement that corresponds to that of another molecule except that the right-to-left sense on one corresponds to the left-to-right sense on the other, the left handedness being known as "levo" or l-x and the righthandedness being known as "dextro" or d-x, where "x" is the referenced molecule.
In two dimensions
In
geometryGeometry arose as the field of knowledge dealing with spatial relationships. Geometry was one of the two fields of pre-modern mathematics, the other being the study of numbers ....
, the mirror image of an object or
two-dimensional figureA 2D geometric model is a geometric model of an object as two-dimensional figure, usually on the Euclidean or Cartesian plane.Even though all material objects are three-dimensional, a 2D geometric model is often adequate for certain flat objects, such as paper cut-outs and machine parts made of...
is the
virtual imageIn optics, a virtual image is an image in which the outgoing rays from a point on the object always diverge. It will appear to converge in or behind the optical device . A simple example is a flat mirror where the image of oneself is perceived at twice the distance from oneself to the mirror...
formed by
reflectionIn mathematics, a reflection is a mapping from a Euclidean space to itself that is an isometry with a hyperplane as set of fixed points; this set is called the axis or plane of reflection. The image of a figure by a reflection is its mirror image in the axis or plane of reflection...
in a
plane mirrorA plane mirror is a mirror with a plane reflective surface.For light rays striking a plane mirror, the angle of reflection equals the angle of incidence...
; it is of the same size as the original object, yet different, unless the object or figure has
reflection symmetryReflection symmetry, reflectional symmetry, line symmetry, mirror symmetry, mirror-image symmetry, or bilateral symmetry is symmetry with respect to reflection. That is, a figure which does not change upon undergoing a reflection has reflectional symmetry.In 2D there is a line of symmetry, in 3D a...
(also known as a P-symmetry).
Two-dimensional mirror images can be seen in the reflections of mirrors or other reflecting surfaces, or on a printed surface seen inside out.
In three dimensions
The concept of mirror image can be extended to
three-dimensionalThree-dimensional space is a geometric 3-parameters model of the physical universe in which we live. These three dimensions are commonly called length, width, and depth , although any three directions can be chosen, provided that they do not lie in the same plane.In physics and mathematics, a...
objects, including the inside parts, even if they are not transparent. The term then relates to structural as well as visual aspects. This is also called
enantiomerIn chemistry, an enantiomer is one of two stereoisomers that are mirror images of each other that are non-superposable , much as one's left and right hands are the same except for opposite orientation. It can be clearly understood if you try to place your hands one over the other without...
or enantiomorph.
If a point of an object has coordinates (x, y,z) then the image of this point (as reflected from the mirror in y, z plane) has coordinates (-x, y,z) - so mirror reflection is a reversal of the coordinate axis perpendicular to the mirror's surface. Thus, a mirror image does not have reversed right and left (or up and down), but rather reversed front and back. The left-right reversal of the mirror image only holds in relation a normal (i.e. unreflected) picture that we see in front of us; see schematic illustration at the right. For instance, if we look at a picture or object in our hand and then turn it towards a mirror, the picture and thus its mirror reflection have made a left-to-right 'flip over' of 180 degrees. The same principle holds when we stand with our back towards the mirror and face a picture or object in front of the mirror, and then compare it with its reflection by turning our head or body 180 degrees towards the mirror. It is thus not the mirror itself, but our own relative position and viewing point that has caused the apparent left-to-right reversal.
A mirror image appears three-dimensional if the observer moves. This is because the relative position of objects changes as the observer's perspective changes.
Looking through a mirror from different positions (but necessarily with the point of observation restricted to the halfspace on one side of the mirror) is like looking at the 3D mirror image of space; without further mirrors only the mirror image of the halfspace before the mirror is relevant; if there is another mirror, the mirror image of the other halfspace is too.
Uses
A text is sometimes deliberately displayed in mirror image, in order to be read through a mirror. Emergency vehicles such as
ambulanceAn ambulance is a vehicle for transportation of sick or injured people to, from or between places of treatment for an illness or injury, and in some instances will also provide out of hospital medical care to the patient...
s or fire engines use mirror images in order to be read from a driver's
rear-view mirrorA rear-view mirror is a mirror in automobiles and other vehicles, designed to allow the driver to see rearward through the vehicle's backlight ....
. Some
movie theaterA movie theater, cinema, movie house, picture theater, film theater is a venue, usually a building, for viewing motion pictures ....
s also use a
Rear Window Captioning SystemThe Rear Window captioning system is a method for presenting, through captions, a transcript of the audio portion of a film in theatres for deaf and hard-of-hearing people. The system was co-developed by WGBH and Rufus Butler Seder....
to assist individuals with
hearing impairment-Definition:Deafness is the inability for the ear to interpret certain or all frequencies of sound.-Environmental Situations:Deafness can be caused by environmental situations such as noise, trauma, or other ear defections...
s watching the film.
Systems of mirrors
In the case of two mirrors, in planes at an angle α, looking through both from the sector which is the intersection of the two halfspaces, is like looking at a version of the world rotated by an angle of 2α; the points of observations and directions of looking for which this applies correspond to those for looking through a frame like that of the first mirror, and a frame at the mirror image with respect to the first plane, of the second mirror. If the mirrors have vertical edges then the left edge of the field of view is the plane through the right edge of the first mirror and the edge of the second mirror which is on the right when looked at directly, but on the left in the mirror image.
In the case of two parallel mirrors, looking through both once is like looking at a version of the world which is translated by twice the distance between the mirrors, in the direction perpendicular to them, away from the observer. Since the plane of the mirror in which one looks directly is beyond that of the other mirror, one always looks at an oblique angle, and the translation just mentioned has not only a component away from the observer, but also one in a perpendicular direction. The translated view can also be described by a translation of the observer in opposite direction. For example, with a vertical
periscopeA periscope is an instrument for observation from a concealed position. In its simplest form it consists of a tube with mirrors at each end set parallel to each other at a 45-degree angle....
, the shift of the world is away from the observer and down, both by the length of the periscope, but it is more practical to consider the equivalent shift of the observer: up, and backward.
See also
- Handedness
Handedness is a human attribute defined by unequal distribution of fine motor skills between the left and right hands. An individual who is more dexterous with the right hand is called right-handed and one who is more skilled with the left is said to be left-handed...
- Flipped image
A flipped image or reversed image, the more formal term, is a static or moving image that is generated by a mirror-reversal of an original across a horizontal axis...
- Flopped image
- Mirror writing
Mirror writing is formed by writing in the direction that is the reverse of the natural way for a given language, such that the result is the mirror image of normal writing: it appears normal when it is reflected in a mirror. It is sometimes used as an extremely primitive form of cipher...
- Relative direction
The most common relative directions are left, right, forward, backward, up, and down. No absolute direction corresponds to any of the relative directions. This is a consequence of the translational invariance of the laws of physics: nature, loosely speaking, behaves the same no matter what...
External links