Interpreting Quantum Theory
Part 1 - What is real and what is not?
Quantum mechanics is a theory of physics developed in the 1920s to describe the behaviour of matter at the atomic scale. In 1924 Louis de Broglie proposed that electrons within an atom are wave-like rather than particle-like. Within two years of this, Erwin Schrödinger had developed his eponymous equation governing the dynamical behaviour of these wave-like entities. Quantum mechanics as we know it today grew directly from this.
Since its foundation in the 1920s, quantum mechanics has proved to be very successful in its predictive power. Despite this success, however, it remains hard to understand quantum mechanics as a description of the world around us. This has led to a long and hotly debated discourse amongst physicists to try to understand whether quantum mechanics should be interpreted as descriptive and explanatory, or modified such that it could be understood that way.
1
The Problem with Quantum Mechanics
The problem with quantum mechanics comes from the nature of the way it answers questions about how physical objects interact with the world around them. The standard interpretation of this theory often represents the state of a physical system using a sum of several separate possibilities where each possibility apparently represents a distinct physical state of the system. These separate possibilities interact with each other in a way that dramatically affects the theory’s predictions.
2
Does the wavefunction really exist?
In the framework of standard quantum mechanics, the wavefunction is at the very least considered to be a complete description of the state of a quantum system. However, there is still no consensus on whether the wavefunction corresponds to a physically real entity or is nothing more than a physically meaningless mathematical construct that helps only in making predictions.
3
The Copenhagen Interpretation: “shut up and calculate”
Textbooks on quantum physics often prevaricate on the question of why a particular interpretation of quantum mechanics is adopted. When this vital question is addressed, the Copenhagen Interpretation tends to be the one offered. Perhaps this is not so surprising given the authority of its originators. As we shall see, the Copenhagen Interpretation asserts that the quantum world is forever unknowable, and this has led some physicists to suggest that any further discussion of interpretation is idle philosophical speculation. We should stop asking inconvenient questions, some say, and just get on with using quantum physics for what it is good at – making predictions.
4
The Modern Perspective
For many physicists today, the Copenhagen Interpretation has by now achieved the status of orthodoxy, at least in terms of is directions for extracting predictions from a wavefunction. However, most would surely be surprised to find that this interpretation requires them to relinquish any assumption of a real physical world at the atomic level. That said, some very eminent proponents of the Copenhagen Interpretation are quite explicit about this requirement. Take the views expressed by Austrian physicist Anton Zeilinger who was awarded the 2022 Nobel Prize for Physics for his experiments with quantum entanglement.
© 2024 Mewburn Ellis
