Coherence definition
Similarly, in a double-slit experiment, if the space between the two slits is increased, the coherence dies gradually and finally the fringes disappear, showing spatial coherence.
Once the fringes are obtained in the Michelson interferometer, when one of the mirrors is moved away gradually from the beam-splitter, the time for the beam to travel increases and the fringes become dull and finally disappear, showing temporal coherence. Both are observed in the Michelson–Morley experiment and Young's interference experiment.
Temporal coherence describes the correlation between waves observed at different moments in time. Spatial coherence describes the correlation (or predictable relationship) between waves at different points in space, either lateral or longitudinal. The amount of coherence can readily be measured by the interference visibility, which looks at the size of the interference fringes relative to the input waves (as the phase offset is varied) a precise mathematical definition of the degree of coherence is given by means of correlation functions. Two waves are said to be coherent if they have a constant relative phase. When interfering, two waves can add together to create a wave of greater amplitude than either one (constructive interference) or subtract from each other to create a wave of lesser amplitude than either one (destructive interference), depending on their relative phase. Constructive or destructive interference are limit cases, and two waves always interfere, even if the result of the addition is complicated or not remarkable. A single wave can interfere with itself, but this is still an addition of two waves (see Young's slits experiment). Interference is the addition, in the mathematical sense, of wave functions. More generally, coherence describes all properties of the correlation between physical quantities of a single wave, or between several waves or wave packets. It contains several distinct concepts, which are limiting cases that never quite occur in reality but allow an understanding of the physics of waves, and has become a very important concept in quantum physics. temporally or spatially constant) interference. Coherence is an ideal property of waves that enables stationary (i.e. In physics, two wave sources are coherent if their frequency and waveform are identical. The winner of the Nobel Peace Prize takes the fight.Equivalence relation on waves with equal frequencies and waveforms I think the total lack of coherence from the administartion shows that Bush is right. Kevin Starr said, “You would need a coherent political culture for such a session to occur” - and the lack of such coherence is exactly the problem - “otherwise it would turn into a food fight from Animal House.” That our society has an interest in coherence and strength and commitment and mutually reinforcing loyalties, then if gay couples want to call their union marriage and a state agrees, and several have now, or a religious body will sanction it - and I don't think the state should be able to stop the religious bodies from saying it - I don't think the rest of us should get in the way of that.īut still: I like a coherent narrative thread, and so far as coherence is possible in personal narratives, why not pursue it? noun logical and orderly and consistent relation of parts.noun the state of cohering or sticking together.noun linguistics Semantic relationship between different parts of the same text.įrom WordNet 3.0 Copyright 2006 by Princeton University.noun physics the property of having the same wavelength and phase.noun Quality of cohering of being coherent internal consistency.noun Connection or dependence, proceeding from the subordination of the parts of a thing to one principle or purpose, as in the parts of a discourse, or of a system of philosophy a logical and orderly and consistent relation of parts consecutiveness.įrom Wiktionary, Creative Commons Attribution/Share-Alike License.noun A sticking or cleaving together union of parts of the same body cohesion.noun Suitable connection or dependence, proceeding from the natural relation of parts or things to each other, as in the parts of a discourse or of any system consistency.įrom the GNU version of the Collaborative International Dictionary of English.noun The act or state of cohering a sticking or cleaving of one thing to another, or of parts of the same body to each other, or a cleaving together of two bodies, as by the force of attraction.noun Physics The property of being coherent, as of waves.noun The quality or state of cohering, especially a logical, orderly, and aesthetically consistent relationship of parts.From The American Heritage® Dictionary of the English Language, 5th Edition.