This is a treatise devoted to the foundations of quantum physics and the role that causality plays in the microscopic world governed by the laws of quantum mechanics. There is no sharp dividing line between physics and philosophy of physics. This is especially true for quantum physics where debate on its interpretation and the status of the various entities postulated has raged in both the scientific and philosophical communities since the 1920s and continues to this day. Although it is readily granted that quantum mechanics produces some strange and counter-intuitive results, it is argued in Quantum Causality that quantum mechanics is not as weird as we might have been led to believe.

The dominant theory of quantum mechanics is called Orthodox Quantum Theory (also known as the Copenhagen Interpretation). Orthodox Quantum Theory is a ‘theoretical tool’ for making predictions for the possible results of experiments on quantum systems and requires the intervention of an observer or an observer’s proxy (e.g. a measuring apparatus) in order to produce predictions. Orthodox Quantum Theory does away with the notion of causality and denies the existence of an underlying quantum realm.

If we are to explain physical reality, a better understanding of the foundations of quantum physics is needed than can be provided by Orthodox Quantum Theory. The way to achieve this understanding is to specify both the ontology and the laws that govern the quantum realm. (A theory’s ontology is the set of assertions about the entities and processes that exist according to the theory.) The Causal Theory of Quantum Mechanics (also known as de Broglie-Bohm Theory) does this by describing micro-phenomena in terms of entities and processes in space and time, thereby embracing causality at the quantum level. Quantum Causality is a philosophical account of the Causal Theory and the place of causality in the quantum realm. Solutions are advanced to the principal conceptual issues that confront the Causal Theory. Conceptual problems occur when a theory is in conflict with another well-established belief. In Quantum Causality, solutions are presented to conceptual problems about the nature of energy, the conservation of energy, fundamental physical forces, and the Pauli Exclusion Principle within the context of the Causal Theory. These issues and their relationships are explored in order to advance understanding of causality in the quantum arena.

The Causal Theory is not well known within the physics community and many physicists who do know of it are generally dismissive in their attitudes. This is a historical legacy inherited by the majority of the physics community from the most influential founders of quantum mechanics, Niels Bohr and Werner Heisenberg. They both denied the independent existence of a quantum level of reality and declared that causality does not apply to quantum events.

Quantum Causality shows that the Causal Theory of Quantum Mechanics is a viable physical theory that provides realistic explanations for quantum phenomena. Much of what is argued for in this book will be controversial but, at the very least, these arguments will likely engender some lively debate on the various issues raised.