A loop line is a type of circuit used in telephone networks. It does not connect to a specific place, and requires two numbers dedicated to it. When one side of the loop is called, there is a tone (called Side A), and on the other there is dead silence (Side B). When a line is connected to side A, any number of lines may be connected to side B (there is usually a limit on this) and be connected into a conference with the person on A. The function of the tone on side A is so that whoever is connected will know when somebody has called the B side and thus connected.
Loop lines are far less common now than they were around 1960, however they reportedly still exist. Because of their nature, however, telephone companies work to protect them (in order to make people use conference calling). The most common methods are:
Filters which bandstop voice (these can be switched on or off)
Recordings which make the line appear out of service
The loop being switched on or off by operators
Restrictions on which lines may call
Using tones in the 1633 column of DTMF, A-D, in the number
Loop quantum gravity (LQG), also known as loop gravity, quantum geometry and canonical quantum general relativity, is a proposed quantum theory of spacetime which attempts to blend together the seemingly incompatible theories of quantum mechanics and general relativity.
The main claimed successes of loop quantum gravity are: (1) that it is a nonperturbative quantization of 3-space geometry, with quantized area and volume operators; (2) that it includes a calculation of the entropy of fl holes; and (3) that it is a viable gravity-only alternative to string theory.
Because the Ashtekar formulation was background-independent, it was possible to use Wilson loops as the basis for a nonperturbative quantization of gravity.
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