When is it ab initio?

[vazumah]

A quantum mechanical model is by definition an ab initio model because it captures all the essential physics of an atom. Using statistical mechanics, it is theoretically possible to build up and calculate all the emergent properties of a material by using the Schrödinger equation.

A model for classical mechanics would be ab initio in its application to macro or continuum scale phenomena where F = ma applies, and no quantum effects are considered. In this case, all the emergent properties of the continuum scale can be modeled by using newton’s laws of motion and the laws of conservation (of energy and momentum).

Classical electromagnetism fails to be an ab initio method because it fails to consider the quantum effects associated with the particle-wave duality of electrons and photons and thus is unable to explain all emergent properties and phenomena associated with electromagnetic waves.

[vazumah]

Addenda: Whilst I initially thought classical electromagnetism was not ab initio – because it doesn’t explain all fundamental or natural phenomena, it turns out to be one. This is because it is formulated on the formal system whose axioms are all derived from Maxwell’s laws and form an internally consistent system and being ab initio does not have any requirements of being true in our world.

The fact that it doesn’t explain all physical phenomena correctly doesn’t mean it is no longer ab initio as a system only fails to be ab initio if it employs phenomenological or empirical data.

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