A consolidating review of Spekkens' toy theory

Understand

In order to better understand a complex theory like quantum mechanics, it is sometimes useful to take a step back and create alternative theories, with more intuitive foundations, and examine which features of quantum mechanics can be reproduced by such a foil theory.

• A prominent example is Spekkens' toy theory, which is based off a simple premise: "What if we took a common classical theory and added the uncertainty principle as a postulate?" In other words, the theory imposes an epistemic restriction on our knowledge about a physical system: only half of the variables can ever be known to an observer.
• Like good science fiction, from this simple principle a rich behaviour emerges, most notoriously when we compose several systems.
• The toy theory emulates some aspects of quantum non-locality, although crucially it is still a non-contextual model.