Spin foam
With the physical concept of spin foam (English spin foam ) consisting of the theory of loop quantum gravity (also loop quantum gravity LQG named) comes, the whole time evolving will spin networks understood. According to the loop quantum gravity, a spin network changes its node-line structure abruptly, i.e. quantized in time. This is where the loop quantum gravity theorists see changes in the quantum state of spacetime. The “foamy” structure is only revealed on the tiny scales of the Planck scale , that is, on characteristic length scales of just cm.
Spin foam and quantum foam
Both the quantum foam (Engl. Quantum foam ), and the spin foam describe physical phenomena that take place on the Planck scale. However, these are fundamentally different things. While the quantum foam represents the curved, foam-like spacetime of the quantum vacuum at a given point in time, the spin foam is not 'real'.
In the loop quantum gravity every time step is discrete . Therefore the spin network exists in one moment in one, and in the other moment immediately in the other (relinked) form. Only if one mentally connects these individual networks from time t1 to time t2 and on to t3 etc., one can speak of a “foam-like structure”.
Figuratively speaking, this form of modeling produces a kind of 'trailing effect', as is known from older (tube) video cameras or, for example, from photo recordings in which very long exposure times are set so that moving lights are photographed at night, stripe-like traces of light on the photo have (see line trace recording ). Just as there is no “real” counterpart in nature for these traces of light in the photo, the image of the spin foam only serves to illustrate the inner dynamics of the spin network in the theory of loop quantum gravity.