The Many Hidden Worlds of Quantum Mechanics

Fasten your seat belts and take off into the realm of multiple, maybe even infinite, worlds. Professor Carroll explains how quantum mechanics predicts the existence of a large number of universes parallel to our own. This far-out theory is one of the leading contenders for a rigorous formulation of quantum mechanics. Trace the history of, and motivation for, this idea.

Investigate the classical picture of reality, which is how physicists thought the world worked before quantum mechanics. Codified by Isaac Newton, classical physics evolved into a nearly unified view based on particles and fields, and it included such revolutionary ideas as Einstein’s theories of relativity. But starting in the early 20th century, scientists began to realize something was amiss.

The widely accepted system of classical physics began to unravel in 1900 when Max Planck proposed an idea that later became known as the quantum. Elaborated by Einstein, this theory held that light waves behave like particles. Later work by Louis de Broglie held that particles sometimes behave like waves. Discover how both ideas were amply confirmed and became tenets of quantum mechanics.

Transition from the old quantum theory to full-fledged quantum mechanics with the mathematically elegant concept of the wave function, derived by Erwin Schrödinger in 1925. Professor Carroll guides you through the terms of the Schrödinger equation, which earned a Nobel Prize for Schrödinger and became the basis for wave mechanics—the theory that predicts how quantum systems behave.

Quantum mechanics was disquieting to anyone trained in classical physics. To dispel this unease, Niels Bohr and Werner Heisenberg devised the “Copenhagen Interpretation.” Delve into the strengths and weaknesses of this influential view, which rejects speculation about what’s “really happening.” One reaction was Schrödinger’s celebrated thought experiment involving a cat in mortal peril.

Consider exactly what Heisenberg meant by his uncertainty principle, which is often misstated, even by physicists. Go deeper into wave-particle duality, studying the famous double-slit experiment, which shows light behaving simultaneously as a wave and a particle. Discover why a realist perspective on Schrödinger’s wave function dissolves some of the key paradoxes of quantum mechanics.