## Understanding Quantum 1

^{th}February 2022

A brief promotion video shows some of the topics and graphics.

Classical physics provided us with an intuitive description of the world about us. It introduced concepts of force, energy and momentum, which combined, are powerful tools for predicting the dynamics of many physical systems. With the coming of the twentieth century the limits of this physics were starting to be found. The limits became apparent with the discovery of the very small building blocks of the universe. A new physics was required for the new fundamental particles of nature.

The new physics drew on classical physics but it required very new abstract concepts to provide accurate predictive powers for the atomic realm. The first lecture will introduce you to the classical concepts that still play a role in quantum physics, and how they have been reinterpreted. In this presentation we will encounter the wave nature of particles.

All the fundamental building blocks possess both a wave and particle nature. The wave is used to predict where a particle may be, and the momenta the particle can possess. The wave nature of a particle places restrictions on where the particle can be, introduces physical constraints and uncertainty into is state. Uncertainty is at the heart of Quantum physics unlike classical physics in which all uncertainty can be eliminated.

We look at the intrinsic quantum nature of elementary particles. One quality called spin provides us with a simple property to model. Quantum mechanics provides a mathematical description of this quantum property with excellent predictive powers. The course does not contain any of the maths but provides you with a graphical model for the maths. We call this the state diagram and apply this model to the polarisation of light.

We then apply the state diagram to location and momentum of a particle to show that both can not be known with absolute precision. This will lead to Heisenberg's Uncertainty principle. The principle is very general and can be applied to many realms of physics, like the interplay between time and energy.

System of particles can behave entangled. Measurement of one particle can affect the result of a measurement on another particle. The act of measurement changes the state of all entangled particles in an instantaneous fashion. This has been show to be the case in countless experiments. Einstein was not happy with this instantaneous action and tried to explain it by other means. Ultimately his description failed and we are left with the very weird nature of the quantum description.

The following course "Understanding Quantum 2" will include Bell's Inequality which when tested experimentally showed that quantum entanglement is real.