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Quantum Mechanics: The Physics of the Microscopic World

Quantum Mechanics: The Physics of the Microscopic World

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Quantum Mechanics: The Physics of the Microscopic World

Course No. 1240
Professor Benjamin Schumacher, Ph.D.
Kenyon College
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Course No. 1240
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Course Overview

One day in 1900, German physicist Max Planck told his son that he had made a breakthrough as important as Isaac Newton's discovery of the workings of the universe. Planck had reached the surprising conclusion that light behaves as if it is packaged in discrete amounts, or quanta, a seemingly simple observation that would lead to a powerful new field of physics called quantum mechanics.

In the following decades, a series of great physicists built on Planck's discovery, including Albert Einstein, Niels Bohr, Louis de Broglie, Werner Heisenberg, Erwin Schrödinger, Richard Feynman, and many others, developing quantum mechanics into the most successful physical theory ever devised—the general framework that underlies our understanding of nature at its most fundamental level.

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 has a broad range of applications 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.

Quantum Mechanics: The Physics of the Microscopic World gives you the logical tools to grasp the paradoxes and astonishing insights of quantum mechanics in 24 half-hour lectures designed specifically for nonscientists and taught by award-winning Professor Benjamin Schumacher of Kenyon College.

No comparable presentation of this subject is so deep, so challenging, and yet accessible. Quantum Mechanics 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, for Professor Schumacher is an innovator in the exciting new discipline of quantum information.

Think Like a Physicist

Working on the principle that any discovery made by the human mind can be explained in its essentials to the curious learner, Professor Schumacher teaches you how to reason like a physicist in working out the features of the quantum world. After taking this course, the following apparently inexplicable phenomena will make sense to you as logical outcomes of quantum processes:

  • That quantum particles travel through space in the form of waves that spread out and are in many places at the same time
  • That quantum mechanics takes us to a bedrock level of reality where objects are utterly simple, identical in every respect
  • That two quantum particles can interact at a distance in a way that seems almost telepathic—a phenomenon that Albert Einstein called "spooky"
  • That even in the complete vacuum of empty space, there is still a vast amount of energy bubbling into and out of existence

Regarding the last phenomenon, you could say that quantum mechanics not only changes our view of everything, it also changes our view of "nothing!"

Quantum Puzzles

Quantum mechanics has even entered popular language with expressions such as "quantum leap," which is often used inaccurately to mean a radical transformation. In quantum mechanics, a quantum leap is the minimum change in the energy level of an electron, related to the discrete units of light energy discovered by Max Planck.

Another familiar expression is the "uncertainty principle," an idea formulated by Werner Heisenberg in the 1920s. Again, popular usage can be misleading, since one often hears the term used to mean the unavoidable disturbance caused by making an observation. But in quantum mechanics the concept refers to an elementary feature of the microworld—that certain properties have no well-defined values at all.

Little wonder that quantum mechanics is one of the few fields in which philosophical speculation goes hand in hand with scientific breakthroughs. Consider these quantum puzzles that have striking philosophical implications:

  • Schrödinger's cat: Erwin Schrödinger noted that the standard Copenhagen interpretation of quantum mechanics makes it possible for a cat to be considered simultaneously dead and alive when exposed to a potentially lethal quantum situation.
  • Bell's theorem: John Bell showed that we must either give up the idea that particles have definite properties before they are measured, or we must imagine that all the particles in the universe are connected by a web of instantaneous communication links.
  • Many-worlds interpretation: In a scenario adopted by many science fiction authors, Hugh Everett III argued that every possible outcome of every quantum event takes place in a limitless branching series of parallel universes—of which we see only one.

Clear, Enlightening, and Thorough

Quantum Mechanics begins by exploring the origin of quantum mechanics and its golden age of discoveries in the early 20th century before taking you deeply into the key concepts and methods of the discipline. Then Professor Schumacher rounds out the course with a discussion of selected topics, including the potentially revolutionary applications of quantum cryptography and quantum computing. Throughout, he adheres to the following very helpful ground rules, tailored to give those without any previous preparation in math and physics a clear, enlightening, and thorough introduction to quantum mechanics:

  • He presents the real theory of quantum mechanics, not a superficial popularization.
  • He simplifies the subject to highlight fundamental principles.
  • He uses thought experiments, or hypothetical examples, as a tool for probing quantum phenomena.
  • He teaches you rudimentary symbols and rules that allow you to calculate the outcome of various quantum experiments.

One thought experiment that Professor Schumacher returns to involves a Mach-Zehnder interferometer, a simple arrangement of mirrors and detectors that illustrates basic properties and paradoxes of quantum mechanics. By considering the different paths that a photon can take through the interferometer, you discover such key principles as constructive and destructive interference, Max Born's probabilistic explanation of quantum phenomena, and Niels Bohr's concept of complementarity that led to the Copenhagen interpretation—the view of quantum mechanics since the 1920s.

Lucid, witty, and intensely interesting, Dr. Schumacher's lectures are illustrated with scores of insightful graphics. You are also introduced to a celebrated visual aid used by physicists themselves: the Feynman diagram, made famous by Nobel Prize–winner Richard Feynman as a cartoon-like shorthand for keeping track of quantum particles as they ceaselessly interact, change their identities, and even move backward through time!

Be Part of a Great Tradition

Richard Feynman was a graduate student of the eminent theoretical physicist John A. Wheeler—and so was Professor Schumacher, who earned the last Ph.D. that Dr. Wheeler supervised. Wheeler, in turn, was mentored by Niels Bohr, who studied with Ernest Rutherford, one of the pioneers of nuclear physics at the turn of the 20th century. Therefore, as you watch Quantum Mechanics, you are part of an unbroken chain of thinkers who have transmitted ideas and added to them across the decades, pondering, probing, and making remarkable discovery after discovery to uncover the secrets of our physical world.

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24 lectures
 |  30 minutes each
Year Released: 2009
  • 1
    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. x
  • 2
    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. x
  • 3
    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. x
  • 4
    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. x
  • 5
    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. x
  • 6
    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. x
  • 7
    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. x
  • 8
    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. x
  • 9
    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. x
  • 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. x
  • 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. x
  • 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. x
  • 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. x
  • 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. x
  • 15
    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. x
  • 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. x
  • 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. x
  • 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. x
  • 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. x
  • 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. x
  • 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. x
  • 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. x
  • 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. x
  • 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. x

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Your professor

Benjamin Schumacher

About Your Professor

Benjamin Schumacher, Ph.D.
Kenyon College
Dr. Benjamin Schumacher is Professor of Physics at Kenyon College, where he has taught for 20 years. He received his Ph.D. in Theoretical Physics from The University of Texas at Austin in 1990. Professor Schumacher is the author of numerous scientific papers and two books, including Physics in Spacetime: An Introduction to Special Relativity. As one of the founders of quantum information theory, he introduced the term qubit,...
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Rated 4.1 out of 5 by 82 reviewers.
Rated 5 out of 5 by Quantum Mechanics: Micro Physcis. A fascinating and intriguing course expertly taught and presented. Excellent graphics animations and video clips. Highly recommended. October 12, 2015
Rated 1 out of 5 by Quantum Mechanics: The Physics of the Microscopic A waste of time. It played around the edges of the subject and never provided substantial value. It is as if the professor never studied math. September 15, 2015
Rated 5 out of 5 by The Epitome of Technical Esoterica, a Good Thing A rare find. Wherever we turn, we are faced with information purporting to have quantum theory as its source. We are told that quantum theory is at the basis of the electronics we use, the light we we see by, and the very earth we stand on. There are books out there that claim the dichotomy between predestination and free will will only be settled at the quantum level. And we are told that quantum entanglement can only be explained in terms of time travel. But it is very rare that we can find an instructor that can explain any of these topics. I took this course in the hopes of, at a minimum, becoming conversant with the vocabulary used in this field, and the fundamental concepts. I hoped that the course would take my level of mathematical sophistication, or lack thereof, into account. I wasn't disappointed. Professor Schumacher is a working researcher in the field. Very well versed in the history of the technology as well as the technical details, he is able to demonstrate the classic experiments in the field and explain them in an understandable manner without the mathematical rigor that few of us could follow. Another theoretical physicist is noted for saying “If you can't explain something simply, you don't understand it.” Professor Shumacher explains things as simply as possible. You will not come out of the course as a theoretical physicist, but if you meet one you may have some interesting questions for him or her, and will probably understand the answers. The professor's own fields of study; quantum computing, quantum cryptography and quantum information are covered well, of course. While these are critically important topics, I admired Professor Schumacher's restraint. The topics were covered, but the professor did not let his personal expertise, and obvious skill and interest, distort the amount of time devoted to these topic at the expense of more general knowledge. He handled the available time well. This is the second course I've taken in which Feynman diagrams were explained. I believe some of it may have stuck this time. And with this, zero point energy made sense. This course will reignite your sense of wonder at this world and the universe in which it is embedded. August 1, 2015
Rated 5 out of 5 by Excellent course This course is excellent and the professor is very engaging. I do not have a broad science background but the material is formatted in easy to understand chunks. Fascinating topic, highly recommended program. July 14, 2015
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