A beam produced by a thermal or other incoherent light source has an instantaneous amplitude and phase which vary randomly with respect to time and position, and thus a very short coherence length.

Thus, in place of God's role as guarantor of the coherence of the world, Kant posits a faculty of reason structured by the forms of our intuition ( our sense of time and space ) and the categories of our understanding ( like the notion of cause and effect ).

The common characteristics are: ( 1 ) radical novelty ( features not previously observed in systems ); ( 2 ) coherence or correlation ( meaning integrated wholes that maintain themselves over some period of time ); ( 3 ) A global or macro " level " ( i. e. there is some property of " wholeness "); ( 4 ) it is the product of a dynamical process ( it evolves ); and ( 5 ) it is " ostensive " ( it can be perceived ).

For an electromagnetic wave, the coherence time is the time over which a propagating wave ( especially a laser or maser beam ) may be considered coherent.

In long-distance transmission systems, the coherence time may be reduced by propagation factors such as dispersion, scattering, and diffraction.

Coherence time, τ, is calculated by dividing the coherence length by the phase velocity of light in a medium ; approximately given by

For example, with a multipath time of 3 μs ( corresponding to a 1 km of added on-air travel for the last received impulse ), there is a coherence bandwidth of about 330 kHz.

Several variants of the coherency matrix have been proposed: the Wiener coherency matrix and the spectral coherency matrix of Richard Barakat measure the coherence of a spectral decomposition of the signal, while the Wolf coherency matrix averages over all time / frequencies.

There are several methods for measuring the temporal coherence of the light ( see: field-autocorrelation ), including the continuous wave Michelson or Fourier transform spectrometer and the pulsed Fourier transform spectrograph ( which is more sensitive and has a much shorter sampling time than conventional spectroscopic techniques, but is only applicable in a laboratory environment ).

The beams interfere, allowing the temporal coherence of the light to be measured at each different time delay setting, effectively converting the time domain into a spatial coordinate.

* Slow fading arises when the coherence time of the channel is large relative to the delay constraint of the channel.

* Fast fading occurs when the coherence time of the channel is small relative to the delay constraint of the channel.

The coherence time of the channel is related to a quantity known as the Doppler spread of the channel.

Since fading depends on whether signal components add constructively or destructively, such channels have a very short coherence time.

In general, coherence time is inversely related to Doppler spread, typically expressed as

where is the coherence time, is the Doppler spread ( Doppler shift ).

Collision detection utilizes time coherence to allow even finer time steps without much increasing CPU demand, such as in air traffic control.

In a slow-fading channel, where the coherence time is greater than the latency requirement, there is no definite capacity as the maximum rate of reliable communications supported by the channel,, depends on the random channel gain.

Temporal coherence describes the correlation or predictable relationship between waves observed at different moments in time.

The coherence time of the wave is infinite since it is perfectly correlated with itself for all delays τ.

The length over which the phase in a beam of light is correlated, is called the coherence length.

This is sometimes referred to as spectral coherence, as it is related to the presence of different frequency components in the wave.

In the case of light emitted by an atomic transition, the coherence length is related to the lifetime of the excited state from which the atom made its transition.

When looking at a cross section of a beam of light, the length over which the phase is correlated is called the transverse coherence length.

In the case of Young's double slit experiment, this would mean that if the transverse coherence length is smaller than the spacing between the two slits, the resulting pattern on a screen would look like two single slit diffraction patterns.

In the case of particles like electrons, neutrons and atoms, the coherence length is related to the spatial extent of the wave function that describes the particle.

This type of set of experiences possesses a constancy and coherence that is lacking in the set of experiences of which hallucinations, for example, are a part.

The interference, however, is seen only when the surfaces are at distances comparable to or smaller than the light's coherence length, which for ordinary white light is few micrometers ; it can be much larger for light from a laser.

The emitted laser light is notable for its high degree of spatial and temporal coherence.

Spatial coherence typically is expressed through the output being a narrow beam which is diffraction-limited, often a so-called " pencil beam.

Temporal ( or longitudinal ) coherence implies a polarized wave at a single frequency whose phase is correlated over a relatively large distance ( the coherence length ) along the beam.

In some media it is possible, by imposing an additional optical or microwave field, to use quantum coherence effects to reduce the likelihood of an excited-state to ground-state transition.

Quantum coherence is an essential difference between classical and quantum theories, and is illustrated by the Einstein-Podolsky-Rosen paradox.

For microscopic bodies, the extension of the system is much smaller than the coherence length, which gives rise to long-range entanglement and other nonlocal phenomena that are characteristic of quantum systems.

Quantum coherence is not typically evident at macroscopic scales-although an exception to this rule can occur at extremely low temperatures ( i. e. approaching absolute zero ), when quantum behavior can manifest itself on more macroscopic scales ( see macroscopic quantum phenomena, Bose-Einstein condensate, and Quantum machine ).

The predominant theory regarding its formation is that the progenitor galaxy was a barred spiral galaxy whose arms had a velocity too great to keep its coherence and therefore detached.

Very often, though, coherence is taken to imply something more than simple logical consistency ; often there is a demand that the propositions in a coherent system lend mutual inferential support to each other.

The degree of coherence is measured by the interference visibility, a measure of how perfectly the waves can cancel due to destructive interference.

Temporal coherence is the measure of the average correlation between the value of a wave and itself delayed by τ, at any pair of times.

Later, C. N. Yang proposed a more generalized measure of macroscopic quantum coherence, called " Off-Diagonal Long-Range Order " ( ODLRO ), that included fermion as well as boson systems.

Because of the limits of the reading ease formulas, some research looked at ways to measure the content, organization, and coherence of text.

Stochastic resonance ( SR ) is a phenomenon that occurs in a threshold measurement system ( e. g., a man-made instrument or device ; a natural cell, organ or organism ) when an appropriate measure of information transfer ( signal-to-noise ratio, mutual information, coherence, d, etc.

Using optical coherence to measure photon pathlength allows OCT to build images of live tissue and clear examinations of tissue morphology.

In this sense, the visibility is a measure of the coherence between two optical fields.

The subsystem can provide us with the coherence between uplink and downlink signals, with the help of which we can measure range-rate Doppler shifts.