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In ordinary language, the word random is used to express apparent lack of purpose or cause. This suggests that no matter what the cause of something, its nature is not only unknown but the consequences of its operation are also unknown. In most technical senses, randomness has an additional positive meaning related to some of the statistical properties of the observed. Thus, the landing location of water droplets from a waterfall will be random in the ordinary sense as it's impossible to determine just what forces have applied to this or that droplet causing it to fall where it does. But in a statistical sense, and depending on the scale of observation, droplet landing spots are not distributed randomly at all. All droplets are confined to a relatively small area about the base of the fall, and within that area have a distinctly non-uniform distribution. On the other hand, the instantaneous sound intensity at any chosen frequency of an electrical circuit noise (eg, 'hiss') is technically random as well as conventionally random.1 Randomness versus unpredictability
Randomness should not be confused with unpredictability which is a related idea in ordinary usage, but unconnected mathematically, and (for many purposes) in physics. For instance, deterministic chaos deals with random phenomena which exhibit organized features at some levels. As another example, the increase of the world human population is quite predictable on average, but individual births and deaths cannot be accurately predicted with any precision in many cases; this small-scale randomness is found in almost all real-world systems, if not as strikingly. Ohm's law and the kinetic theory of gases are statistically reliable descriptions of the 'sum' (ie, the net result or integration) of vast numbers of individual micro events, each of which are random and none of which are individually predictable. All we directly perceive is circuit noise and some bulk gas behaviors.
In some applications, both randomness (as tested statistically) and unpredictability are required, as for instance in most uses of cryptography. In other applications, such as many modeling or simulation applications, unpredictability is not only unnecessary, but may cause problems as for instance whilst repeating modeling runs during model 'acceptance tests'.
Sensibly dealing with randomness is a seriously hard problem in modern science, mathematics, psychology and philosophy. Merely defining it adequately for the purposes of this or that discipline has been quite difficult. Distinguishing between apparent randomness and actual randomness has been no easier, and additionally assuring unpredictability, especially against a well motivated party (in cryptographic parlance, the "Adversary"), has been harder still.
2 Randomness in philosophy
Note that the bias that "everything has a purpose or cause" is actually implicit in the expression "apparent lack of purpose or cause". Humans are always looking for patterns in their experience, and the most basic pattern seems to be cause/effect. This appears to be deeply embedded in the human brain, and perhaps in other animals as well. For example, dogs and cats often have been reported to have apparently made a cause and effect connection that strikes us as amusing or peculiar. (See classical conditioningClassical conditioning also called "pavlovian conditioning" and "respondent conditioning", is a type of learning involving animals, caused by the association (or pairing) of two stimuli. The simplest form of classical conditioning is reminiscent of what A). For instance there is a report of a dog who, after a visit to a vet whose clinic had tile floors of a particular kind, refused thereafter to go near such a tiled floor, whether or not it was at a vet's.
It is because of this bias that the absence of a causeThe philosophical concept of Causality or Causation refers to the set of all particular "causal" or "cause-and-effect" relations. The Differentia (distinguishing properties/characteristics) of Causality which all causal relations have in common: The relat seems problematic. See causation.
To solve this 'problem', random events are sometimes said to be caused by chanceChance can be used in any of the following contexts: Probability Luck Randomness Chance is also a 2002 movie starring Amber Benson.. Rather than solving the problem of randomness, this opens the gaping hole of the ontological status of chance. It is hard to avoid circularity by defining chance in terms of randomness.
