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One universe is not enough. Learn about the Many-Worlds Interpretation of quantum mechanics in this exciting course taught by a renowned expert.

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1. Why Suppose There's More Than One World?

32m

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.

2. The Classical Physics World That Never Was

31m

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.

3. Quantum Worlds Start With Waves and Particles

29m

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.

4. A Wave Function to Describe Particles

27m

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.

5. Copenhagen Says the Wave Function Collapses

28m

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.

6. Is the Wave Function Real?

31m

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.

7. Uncertainty in Action With Spin and Qubits

29m

Explore the fundamental quantum property of particles known as "spin," which can come in binary states, like the 0 and 1 bits in digital computing. For the purposes of quantum computing, spin can serve as a "qubit" to encode information at the subatomic level. Learn how spin makes the uncertainty principle much easier to understand and provides deep insights into the nature of the quantum world.

8. Quantum Entanglement and Action at a Distance

33m

Focus on Einstein's objection to a specific feature of quantum mechanics called entanglement, which he termed, "spooky action at a distance." When two particles are entangled, no matter how far apart they are, if you measure the property of one, you instantly know the corresponding property of the other. Einstein tried to use this feature to argue that quantum mechanics must be incomplete.

9. Entanglement Leads to Many Worlds

31m

Use concepts developed in the course so far to learn how physicist Hugh Everett arrived at a bold new approach to quantum mechanics. Called the Many-Worlds Interpretation, it holds that the wave function represents reality and evolves smoothly into multiple distinct worlds when a quantum measurement takes place. Contrast Everett's straightforward idea with the opaque Copenhagen Interpretation.

10. Decoherence Explains Branching Worlds

30m

Focus on decoherence, which does the same work in Many-Worlds as the collapse of the wave function in the Copenhagen Interpretation. Both explain what happens when a measurement is made, but in Many-Worlds the mechanism is more consistent with the underlying physics. Then, see how decoherence is the gateway to multiple branching worlds, which differ from the cosmological idea of the multiverse.

Extended Details

SeriesMany Hidden Worlds of Quantum Mechanics

Closed CaptionsEnglish

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The Great CoursesDirector

The Great CoursesProducer

Sean CarrollActor

Many Hidden Worlds of Quantum Mechanics

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