Quantum Spin Foam

A spin foam in loop quantum gravity is an extension of the mathematics of spin networks to include time and space.

A spin network consists of nodes and links which create a net-like graph, similar to a woven cloth with thread for links and nodes where the threads cross. Now if the nodes are associated with small units of volume (quanta of volume) and the links are associated with small units of area (quanta of area) then when time enters the picture the points get extended as lines and the lines extend as sheets. The whole thing creates something that resembles the borders between soap bubbles. Therefore, the term foam. 

Now spin is related to quantum spin which is an intrinsic and unique property of sub-atomic particles and is not the same as normal angular momentum. The quantum spin numbers are used in the mathematics that construct spin networks. Since spin is quantized, having only whole or half values the resulting spacetime is quantized leading to quantum gravity.

Spacetime then emerges from a spin network, a graph-like net structure propagated through time . . .

Source:
Sci-pedia - The Online Resource for Science - Quantum Spin Foam

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