Quantum Mechanics: The Physics of the Microscopic World

Overview

Course No. 1240

Peer into the strange and wonderful world of quantum physics with this course that explains how the quantum world works and why it works that way. Quantum mechanics gives us a picture of the world that is so radically counterintuitive that it has changed our perspective on reality itself, raising profound questions about concepts such as cause and effect, measurement, and information.

Despite its seemingly mysterious nature, quantum mechanics is already broadly applied in fields such as chemistry, computer science, and cryptography. It also plays an important role in the development and innovation of some of today’s most amazing—and important—technologies, including lasers, transistors, microscopes, semiconductors, and computer chips.

This course gives you the logical tools to grasp the paradoxes and astonishing insights of quantum mechanics in 24 half-hour lectures designed specifically for nonscientists. No comparable presentation of this subject is so deep and so challenging, yet still eminently accessible. Quantum Mechanics: The Physics of the Microscopic World is generously illustrated with diagrams, demonstrations, and experiments and is taught by a professor who is both a riveting lecturer and a pioneer in the field.

Working on the principle that any discovery made by the human mind can be explained in its essentials to the curious learner, award-winning Professor Benjamin Schumacher teaches you how to reason like a physicist in working out the features of the quantum world. You will gain a deeper understanding of things like a “quantum leap” and the “uncertainty principle,” both of which have been used—and misused—in popular culture. Lucid, witty, and intensely interesting, Professor Schumacher’s lessons will resonate with you long after you have finished watching them.

Video Lectures

01: The Quantum Enigma

Quantum mechanics is the most successful physical theory ever devised, and you learn what distinguishes it from its predecessor, classical mechanics. Professor Schumacher explains his ground rules for the course, which is designed to teach you some of the deep ideas and methods of quantum mechanics.

Duration: 32 min

02: The View from 1900

You investigate the age-old debate over whether the physical world is discrete or continuous. By the 19th century, physicists saw a clear demarcation: Matter is made of discrete atoms, while light is a continuous wave of electromagnetic energy. However, a few odd phenomena remained difficult to explain.

Duration: 32 min

03: Two Revolutionaries-Planck and Einstein

At the beginning of the 20th century, Max Planck and Albert Einstein proposed revolutionary ideas to resolve puzzles about light and matter. You explore Planck’s discovery that light energy can only be emitted or absorbed in discrete amounts called quanta, and Einstein’s application of this concept to matter.

Duration: 28 min

04: Particles of Light, Waves of Matter

Light propagates through space as a wave, but it exchanges its energy in the form of particles. You learn how Louis de Broglie showed that this weird wave-particle duality also applies to matter, and how Max Born inferred that this relationship makes quantum mechanics inherently probabilistic.

Duration: 28 min

05: Standing Waves and Stable Atoms

You explore the mystery of why atoms are stable. Niels Bohr suggested that quantum theory explains atomic stability by allowing only certain distinct orbits for electrons. Erwin Schrödinger discovered a powerful equation that reproduces the energy levels of Bohr’s model.

Duration: 30 min

06: Uncertainty

One of the most famous and misunderstood concepts in quantum mechanics is the Heisenberg uncertainty principle. You trace Werner Heisenberg’s route to this revolutionary view of subatomic particle interactions, which establishes a trade-off between how precisely a particle’s position and momentum can be defined.

Duration: 30 min

07: Complementarity and the Great Debate

You focus on the Einstein-Bohr debate, which pitted Einstein’s belief that quantum events can, in principle, be known in every detail, against Bohr’s philosophy of complementarity—the view that a measurement of one quantum variable precludes a different variable from ever being known.

Duration: 29 min

08: Paradoxes of Interference

Beginning his presentation of quantum mechanics in simplified form, Professor Schumacher discusses the mysteries and paradoxes of the Mach-Zehnder interferometer. He concludes with a thought experiment showing that an interferometer can determine whether a bomb will blow up without necessarily setting it off.

Duration: 30 min

09: States, Amplitudes, and Probabilities

The interferometer from the previous lecture serves as a test case for introducing the formal math of quantum theory. By learning a few symbols and rules, you can describe the states of quantum particles, show how these states change over time, and predict the results of measurements.

Duration: 31 min

10: Particles That Spin

Many quantum particles move through space and also have an intrinsic spin. Analyzing spin gives you a simple laboratory for exploring the basic ideas of quantum mechanics, and it is one of your key tools for understanding the quantum world.

Duration: 33 min

11: Quantum Twins

Macroscopic objects obey the snowflake principle. No two are exactly alike. Quantum particles do not obey this principle. For instance, every electron is perfectly identical to every other. You learn that quantum particles come in two basic types: bosons, which can occupy the same quantum state; and fermions, which cannot.

Duration: 31 min

12: The Gregarious Particles

You discover that the tendency of bosons to congregate in the same quantum state can lead to amazing applications. In a laser, huge numbers of photons are created, moving in exactly the same direction with the same energy. In superconductivity, quantum effects allow electrons to flow forever without resistance.

Duration: 30 min

13: Antisymmetric and Antisocial

Why is matter solid, even though atoms are mostly empty space? The answer is the Pauli exclusion principle, which states that no two identical fermions can ever be in the same quantum state.

Duration: 31 min

14: The Most Important Minus Sign in the World

At the fundamental level, bosons and fermions differ in a single minus sign. One way of understanding the origin of this difference is with the Feynman ribbon trick, which Dr. Schumacher demonstrates.

Duration: 30 min

15: Entanglement

When two particles are part of the same quantum system, they may be entangled with each other. In their famous “EPR” paper, Einstein and his collaborators Boris Podolsky and Nathan Rosen used entanglement to argue that quantum mechanics is incomplete. You chart their reasoning and Bohr’s response.

Duration: 28 min

16: Bell and Beyond

Thirty years after EPR, physicist John Bell dropped an even bigger bombshell, showing that a deterministic theory of quantum mechanics such as EPR violates the principle of locality—that particles in close interaction can’t be instantaneously affected by events happening in another part of the universe.

Duration: 30 min

17: All the Myriad Ways

Feynman diagrams are a powerful tool for analyzing events in the quantum world. Some diagrams show particles moving forward and backward in time, while other particles appear from nowhere and disappear again. All are possible quantum scenarios, which you learn how to plot.

Duration: 32 min

18: Much Ado about Nothing

The quantum vacuum is a complex, rapidly fluctuating medium, which can actually be observed as a tiny attraction between two metal plates. You also discover that vacuum energy may be the source of the dark energy that causes the universe to expand at an ever-accelerating rate.

Duration: 31 min

19: Quantum Cloning

You explore quantum information and quantum computing—Dr. Schumacher’s specialty, for which he pioneered the concept “qubit,” the unit of quantum information. You learn that unlike classical information, such as a book or musical recording, quantum information can’t be perfectly copied.

Duration: 29 min

20: Quantum Cryptography

The uncopyability of quantum information raises the possibility of quantum cryptography—an absolutely secure method for transmitting a coded message. This lecture tells how to do it, noting that a handful of banks and government agencies already use quantum cryptography to ensure the security of their most secret data.

Duration: 31 min

21: Bits, Qubits, and Ebits

What are the laws governing quantum information? Charles Bennett has proposed basic rules governing the relationships between different sorts of information. You investigate his four laws, including quantum teleportation, in which entanglement can be used to send quantum information instantaneously.

Duration: 32 min

22: Quantum Computers

You explore the intriguing capabilities of quantum computers, which don’t yet exist but are theoretically possible. Using the laws of quantum mechanics, such devices could factor huge numbers, allowing them to easily decipher unbreakable conventional codes.

Duration: 30 min

23: Many Worlds or One?

What is the fundamental nature of the quantum world? This lecture looks at three possibilities: the Copenhagen, hidden-variable, and many-worlds interpretations. The first two reflect Bohr’s and Einstein’s views, respectively. The last posits a vast, multivalued universe encompassing every possibility in the quantum realm.

Duration: 30 min

24: The Great Smoky Dragon

In this final lecture, you ponder John A. Wheeler’s metaphor of the Great Smoky Dragon, a creature whose tail appears at the start of an experiment and whose head appears at the end. But what lies between is as uncertain as the mysterious and unknowable path of a quantum particle.

Duration: 30 min