Lux Aeterna was a lattice of point singularities at the points where the dimensions of the Higher Place and the Six-Fold Ream of Calabi-Yau Space crossed. It was described to be the eleven-dimensional quantum foam which underlies the structure of reality.
Advanced enough technology like the Master's TARDIS can tap into the power of this quantum foam and be bestowed with nigh-omnipotent power, as seen with the birth of the entity known as the Quantum Archangel. The Lux Aeterna was the food source of the Chronovores. (PROSE: The Quantum Archangel)