The interpretation states that the wave function does not apply to an individual system – for example, a single particle – but is an abstract statistical quantity that only applies to an ensemble (a vast multitude) of similarly prepared systems or particles.

The modern concept of quantization is about values that, in the classical context, are numbers, being replaced with quantum-mechanical quantities (Dirac called them q-numbers), often represented by function operators.

If the first pillar of the Ithaca interpretation is that correlations are the only fundamental and objective properties of the world, the second is that the density matrix of a system is a fundamental objective property of that system whether or not it is a one-dimensional projection operator.

Quantum mechanics is the field of physics that explains how extremely small objects simultaneously have the characteristics of both particles (tiny pieces of matter) and waves (a disturbance or variation that transfers energy). Physicists call this the “wave-particle duality.”