### random walk

(movement with random turns)

The term **random walk** is used for a kind of motion
(or mathematically-equivalent process) where after some length in
one direction, the direction shifts to an unrelated random direction.
The concept is used to describe/model some processes, including
some in financial investing, some in biology, as well some
in physics, e.g., **statistical physics**.

For example, in radiative transfer, when a photon
is absorbed by an atom, and later one is emitted, the direction
of the new photon is random, having no relation to the direction
of the one earlier received.

Mathematical properties of random walks are studied, one being
that the average straight-line distance traveled after N such
random travel legs is the length of "the square root N" legs.
Given the radiative transfer example, this means photons
leaving stars have been absorbed and re-emitted on the order of the
square of the number of legs (average distance a photon travels
before being re-absorbed) that would be necessary if the photon's
direction was always outward. For the Sun, a typical leg in
the photon's journey is on the order of a centimeter and it can
take thousands or even a million years for a photon to leave the
Sun after the creation of the photon (by the heat from fusion
in the stellar core) that began the random walk.

(*mathematics,simulation,computation*)
http://en.wikipedia.org/wiki/Random_walk

**Referenced by:**

spectral energy distribution (SED)

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