Black box


In science, computing, and engineering, a black box is a device, system or object which can be viewed in terms of its inputs and outputs, without any knowledge of its internal workings. Its implementation is "opaque". Almost anything might be referred to as a black box: a transistor, an engine, an algorithm, the human brain, an institution or government.
To analyse something modeled as an open system, with a typical "black box approach", only the behavior of the stimulus/response will be accounted for, to infer the box. The usual representation of this black box system is a data flow diagram centered in the box.
The opposite of a black box is a system where the inner components or logic are available for inspection, which is most commonly referred to as a white box.

History

The modern meaning of the term "black box" seems to have entered the English language around 1945. In electronic circuit theory the process of network synthesis from transfer functions, which led to electronic circuits being regarded as "black boxes" characterized by their response to signals applied to their ports, can be traced to Wilhelm Cauer who published his ideas in their most developed form in 1941. Although Cauer did not himself use the term, others who followed him certainly did describe the method as black-box analysis. Vitold Belevitch puts the concept of black-boxes even earlier, attributing the explicit use of two-port networks as black boxes to Franz Breisig in 1921 and argues that 2-terminal components were implicitly treated as black-boxes before that.
In cybernetics, a full treatment was given by Ross Ashby in 1956. A black box was described by Norbert Wiener in 1961 as an unknown system that was to be identified using the techniques of system identification. He saw the first step in self-organization as being to be able to copy the output behavior of a black box. Many other engineers, scientists and epistemologists, such as Mario Bunge, used and perfected the black box theory in the 1960s.

System theory

In systems theory, the black box is an abstraction representing a class of concrete open system which can be viewed solely in terms of its stimuli inputs and output reactions:
The understanding of a black box is based on the "explanatory principle", the hypothesis of a causal relation between the input and the output. This principle states that input and output are distinct, that the system has observable inputs and outputs and that the system is black to the observer.

Recording of observed states

An observer makes observations over time. All observations of inputs and outputs of a black box can be written in a table, in which, at each of a sequence of times, the states of the box’s various parts, input and output, are recorded. Thus, using an example from Ashby, examining a box that has fallen from a flying saucer might lead to this protocol:
TimeStates of input and output
11:18I did nothing—the Box emitted a steady hum at 240 Hz.
11:19I pushed over the switch marked K: the note rose to 480 Hz and remained steady.
11:20I accidentally pushed the button marked “!”—the Box increased in temperature by 20 °C.
11:21Etc.
Thus every system, fundamentally, is investigated by the collection of a long protocol, drawn out in time, showing the sequence of input and output states. From this there follows the fundamental deduction that all knowledge obtainable from a Black Box is such as can be obtained by re-coding the protocol ; all that, and nothing more.
If the observer also controls input, the investigation turns into an experiment, and hypotheses about cause and effect can be tested directly.
When the experimenter is also motivated to control the box, there is an active feedback in the box/observer relation, promoting what in control theory is called a feed forward architecture.

Modeling

The modeling process is the construction of a predictive mathematical model, using existing historic data.

Testing the black box model

A developed black box model is a validated model when black-box testing methods ensures that it is, based solely on observable elements.
With backtesting, out of time data is always used when testing the black box model. Data has to be written down before it is pulled for black box inputs.

Other theories

Black box theories are things defined only in terms of their function. The term black box theory is applied to any field, philosophy and science or otherwise where some inquiry or definition is made into the relations between the appearance of something, i.e. here specifically the thing's black box state, related to its characteristics and behaviour within.
Specifically, the inquiry is focused upon a thing that has no immediately apparent characteristics and therefore has only factors for consideration held within itself hidden from immediate observation. The observer is assumed ignorant in the first instance as the majority of available data is held in an inner situation away from investigations. The black box element of the definition is shown as being characterised by a system where observable elements enter a perhaps imaginary box with a set of different outputs emerging which are also observable.

Adoption in humanities

In humanities disciplines such as philosophy of mind and behaviorism, one of the uses of black box theory is to describe and understand psychological factors in fields such as marketing when applied to an analysis of consumer behaviour.
The black box theory of consciousness states that the mind is fully understood once the inputs and outputs are well-defined.

Black box theory

Black Box theory is even wider in application than professional studies:

Applications

Computing and mathematics