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Quantum Mechanics

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 is rated 4.2 out of 5 by 135.
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Rated 5 out of 5 by from Transcript Required? Sometimes a brilliant lecturer says something before its importance becomes clear. Unfortunately, rewinding videos to “double-check” is frustrating. This course’s Guidebook is absolutely inadequate to save you – so a Transcript is extremely useful. There is no severe math - though one must become facile with “ket” diagrams (Lecture 19 = L19). COMMENTS: 1.) The Great Course “Understanding the Quantum World" by Carlson (see my December 2020 Review) is a great intro to quantum mechanics. Schumacher’s course is a much deeper dive – smashingly interesting, though parts are beyond comprehension for those not specifically gifted to its study. Recommend Carlson’s course first then attempt Schumacher’s if you want more or if this will be your area of study. 2.) In 1992, Schumacher and a friend (L19) proposed “cubit” as the new measure of quantum info. This was a pun on “qubit”, the 4000-year-old length unit used in Noah’s Ark (Gen 6:15,16), forging a link between the Beginning and ancient flood civilization stories that appear across many cultures. 3:) Feynman's -1/2 spin, 1+ spin "belt trick" illustration of spin and rotation is fun with kids (though it may not lead them into physics) and is an important part of the following proposed two column Course Outline: [Column 1] FERMIONS, -1/2 spin, belt loop 360 degrees unwind negative, antisocial Fermi-Dirac particles with antisymmetric state when particles exchange, quantum energy states, example: solids // [Column 2] BOSONS, 1+ spin, belt loop 720 degrees unwind positive, social Bose-Einstein particles with symmetric particle exchange, example: lasers. HIGHLIGHTS: L1 course THEME: "there is energy present even in empty space, even when there are no particles.” L3’s classical question on the theory of heat: why don’t you wear sunscreen around a light bulb? L4 course PILLAR: “Everything...has both wave and particle properties. Light, for example, “travels as a wave (but) interacts as a particle." L6 Heisenberg's indeterminacy principle tells us there is a trade-off “due to wave-particle duality” of quantum mechanics. This accounts for why large objects don’t “seem to act" like atomic scale objects. How so? We can know large-scale (example: a baseball) objects’ position (delta m) and momentum (delta p) to be greater than (the extremely small) Plank's constant. On the atomic scale, these quantities are smaller, leading to uncertainty of position and momentum. L13's Pauli's exclusion principle explains why matter occupies space. L8: Wheeler’s quantum mechanics motto: “No phenomenon is a phenomenon until observed” causes difficulty on the quantum level where observation changes the observed! L9 dives into quantum systems, kets, quantum amplitudes, the Rule of Superposition, Born's Rule of Probability, Update Rule 1 for non-random states, and Update Rule II where states update randomly. To these, L15 adds the Composition Rule: the state of 2 or more particles is a simple or superposition of particle states. L11/L12: No two macro-objects have the same atomic arrangement and obey the "snowflake principle". L12: Boson interactions: an atom can absorb a photon, jump down to a lower state and emit a photon, OR an excited atom can add a photon to passing photons going in a particular direction (as in a laser). L17: Virtual particles can come and go in a vacuum if their energy times their life is less than Planck’s constant (i.e.: “they stay beneath…the time-energy uncertainty principle); an electron "moving through space (is) surrounded by swarms of virtual photons, virtual electron-positron pairs." “Though there are some infinities…they can be cancelled out by this…voodoo of renormalization.” L18: “The quantum vacuum is a complex, seething, rapidly fluctuating medium"…that “may be the source of the dark energy” expanding the universe at an accelerating rate. L19: there is no cloning of quantum information. L19: Cubit basis superposition and entanglement. L20-24: applications of quantum mechanics. [This course was a gift].
Date published: 2024-03-27
Rated 3 out of 5 by from Bad Math In general an interesting course, but his math is bad. In lesson 12 discussing bosons, he claims half the time, the bosons are in the same box and half the time they are in separate boxes. WRONG, WRONG, WRONG !!!! If the bosons randomly go into boxes, they will go into box ab twice as often as aa. Yes they are indistinguishable, so there are only six possible observations, but that doesn't equate to percentage. According to his logic, if he rolls a red die and a green die, and I roll two red dice, I will get doubles twice as often as he will. Anyone who has ever played with dice knows this is incorrect. I hope he never goes to Vegas. If Quantum Mechanics is based on this type of math, I guess I have just broken the theory.
Date published: 2024-01-31
Rated 5 out of 5 by from Great introduction to the subject! I came into this course with a little knowledge of the topic, but not much. Some lectures in the course were more challenging than others, but the professor does a great job of explaining and demonstrating the concepts in a way that beginners can understand. A fascinating subject!
Date published: 2024-01-10
Rated 5 out of 5 by from Dreams are Quantum Computing When you reduce the complexity of this concept as is done here, it can easily apply to a Psychology computation of the mind model. Instructor is fantastic at explaining and simplifying.
Date published: 2023-08-29
Rated 5 out of 5 by from Insightful and entertaining I studied quantum mechanics at the Masters level, and it was one of the hardest, most arcane courses I ever took. The professors were all brilliant but they never converted the mathematical equations into an understanding of their deeper meaning. At least, not for me. Im enjoying this course immensely for its clarity around the meaning of the mathematics … like, what does Schrodinger’s wave equation really mean!? Instead of memorizing Greek letters. The professor, Benjamin Schumacher, has a down-to-earth style, clear explanations, simplified a bit of course but absolutely enlightening to all the basic concepts. Highly recommended.
Date published: 2022-10-31
Rated 5 out of 5 by from Wonderful Over 35 years, I've watched lots of physics programs and read lots of physics books, as a layperson. Dr. Schumacher clarified some things that were fuzzy to me, even after I tried to get my head around them (Bell's inequality, for one). This is a great series of lectures, and I'll be watching some of them over to further absorb the ideas.
Date published: 2022-06-28
Rated 1 out of 5 by from Lecture One links to Lecture Two, please fix it. I did not listen to it, because lecture one is missing. From the web site (using browser), Lecture One links to Lecture Two, please fix it.
Date published: 2022-06-05
Rated 5 out of 5 by from Best Professor In my view the professor makes the course. Professor Schumacher has presented this complex subject in a way that opens it to the average person. I have taken several courses that touch on the subject of quantum mechanics, but this one is by far the best in terms of increasing my capability to grasp difficult concepts. His teaching method, clear examples, and obvious enthusiasm for the subject made this course a pleasure for me.
Date published: 2021-10-13
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Quantum mechanics gives us a picture of the world so radically counterintuitive that it has changed our perspective on reality itself. In Quantum Mechanics: The Physics of the Microscopic World, award-winning Professor Benjamin Schumacher gives you the logical tools to grasp the paradoxes and astonishing insights of this field. Designed specifically for nonscientists, these 24 lectures reveal breathtaking discoveries that are helping us unlock the secrets of the universe.


Benjamin Schumacher

Gravity is about both phenomena near at hand at the human scale, everyday and intuitive, and phenomena far off at an astronomical scale.


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, invented quantum data compression (also known as Schumacher compression), and established several fundamental results about the information capacity of quantum systems. For his contributions, he won the 2002 Quantum Communication Award, the premier international prize in the field, and was named a Fellow of the American Physical Society. Besides working on quantum information theory, he has done physics research on black holes, thermodynamics, and statistical mechanics. Professor Schumacher has spent sabbaticals working at Los Alamos National Laboratory and as a Moore Distinguished Scholar at the Institute for Quantum Information at California Institute of Technology. He has also done research at the Isaac Newton Institute of Cambridge University, the Santa Fe Institute, the Perimeter Institute, the University of New Mexico, the University of Montreal, the University of Innsbruck, and the University of Queensland.

By This Professor

Black Holes, Tides, and Curved Spacetime: Understanding Gravity
Quantum Mechanics
The Science of Information: From Language to Black Holes
Impossible: Physics Beyond the Edge
Quantum Mechanics


The Quantum Enigma

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.

32 min
The View from 1900

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.

32 min
Two Revolutionaries-Planck and Einstein

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.

28 min
Particles of Light, Waves of Matter

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.

28 min
Standing Waves and Stable Atoms

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.

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.

30 min
Complementarity and the Great Debate

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.

29 min
Paradoxes of Interference

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.

30 min
States, Amplitudes, and Probabilities

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.

31 min
Particles That Spin

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.

33 min
Quantum Twins

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.

31 min
The Gregarious Particles

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.

30 min
Antisymmetric and Antisocial

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.

31 min
The Most Important Minus Sign in the World

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.

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.

28 min
Bell and Beyond

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.

30 min
All the Myriad Ways

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.

32 min
Much Ado about Nothing

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.

31 min
Quantum Cloning

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.

29 min
Quantum Cryptography

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.

31 min
Bits, Qubits, and Ebits

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.

32 min
Quantum Computers

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.

30 min
Many Worlds or One?

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.

30 min
The Great Smoky Dragon

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.

30 min

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