Understanding the Quantum World

Rated 4 out of 5 by from Needs one more lecture Erica is truly an outstanding teacher. Perhaps the best I have ever experienced. That being said, I think that somewhere early in the class, a major discussion of Planck's Constant should have been endeavored. Having taken previous classes, I am familiar with what this is, but she does not discuss this at all. As it is fundamental to Einstein's discovery, that all energy and matter are "Quantized" rather than a continuous substance, and thus forms the basis for all of Quantum Mechanics, I find this to be a very serious omission. Still a fantastic class
Date published: 2021-01-07
Rated 5 out of 5 by from Great explanations and simplifications Truly amazing analogies makes complex and strange phenomena understandable and enjoyable
Date published: 2021-01-06
Rated 2 out of 5 by from Frustrating! Every time this course gets close to revealing something interesting, it retreats into a (slightly childish) analogy. I think it's to avoid using any mathematics to explain what's happening. I quit in the middle of lecture 10 because I got SO frustrated--instead of showing even interested diagrams, it circled back to telling me what a tetrahedron is again, or reiterating that the atoms are shaking hands. Maybe for someone who was badly afraid of mathematics, this would be a good and accessible overview of quantum theory... although, given that some of the math involved is actually very simple (as long as you don't have to do the actual calculations from scratch) this would ALSO be an excellent opportunity to make the math less frightening. I'm just so frustrated with the way this keeps coming close to being interesting, then running away from the interesting parts lest it be scary.
Date published: 2020-12-29
Rated 5 out of 5 by from Just terrific I have only finished a quarter of this course, and normally I would not presume to write a review of any course until I had watched all the lectures, but in this case I am making an exception because the lecture I just watched on the Heisenberg uncertainty principle was simply the best explanation of that principle I have ever come across. I have read a number of books on quantum mechanics, and the nature of the uncertainty principle is not consistently explained. Some books describe it as merely an observer effect. That is, they say uncertainty arises because we cannot measure a system without affecting the system, especially at the quantum level. This is easy enough to understand, and I gather Heisenberg himself sometimes offered this “explanation" for his principle, but other books say this is incorrect and misleading. Rather, they say the correct explanation is that uncertainty is inherent in the nature of quantum particles and has nothing to do with measurement problems. The reason for this inherent uncertainty, however, was always a little vague. Consequently, I was left in the frustrating position of having one explanation that I could understand, but was apparently wrong, and a second that I did not understand, but was apparently correct. Professor Carlson finally cleared things up for me. She confirmed that uncertainty is inherent in the nature of quantum particles, and more importantly, gave me a clear, if rudimentary, explanation of why that is so. Thank you! I obviously can not speak to the lectures I have yet to watch, but all of the first six lectures have been excellent, and the last one alone was worth the price of admission.
Date published: 2020-12-23
Rated 5 out of 5 by from Wow! ...Just wow! Carlson has produced a seamless path from the concepts behind the quantum world’s equations to its real world applications. She constantly acknowledges the superficiality of what we understand about reality. This magnifies rather than detracts from her presentation. As she frequently points out, our world would simply not work without the quantum mysteries that we observe but whose basis we do not understand. Chemistry would not exist (L24), electricity would not flow, the ultraviolet catastrophe would occur, etc. Once one listens to Carlson, one understands an idea very critical to existence: that idea is Wolfgang Pauli’s 1940 conclusion (L21) that while fermions must obey the Pauli exclusion principle, particles that have integral spin (bosons) do not. This summation of the quantum world is simple in concept (after Carlson explains it), but obtuse in its scientific explanation. She then points out Feynman’s opinion that it “…might mean that we don’t have a really deep understanding...“ of the very basics of our reality. PROS: Carlson’s steady presentation is backed with a confidence that exudes contagious enthusiasm. Great precision is required to separate what is observable on the quantum level from that on the macro level. Carlson also constantly reviews concepts in slightly different ways. This keeps one from drowning when not quite sure about a prior concept. Her clear analogies are invaluable. She continues to refer back to prior ideas throughout the course in a manner that crystallizes, without boring. The 20-item course quiz causes a thorough mental review of the course. Kudos go to her & The Great Courses' staff for an absolutely marvelous Guidebook and excellent teaching aides. CONS are minor: 1. Be careful at about 26:21 in L6, where the screen aid suddenly flips a correct equation into an incorrect one that is at odds with what Carlson is saying. 2. Guidebook quibble: Quantum tunneling in USB drives (L20) was important enough to make it to the Quiz, but was not included in the Guidebook. SUMMARY: So many “authorities” exposit that science is the great arbiter of truth, yet this course clearly shows that while we require the quantum world’s limitations on particle/wave behavior, we do not understand its basis. 80 years after Schrodinger, Heisenberg, Einstein, et al provided their important limitations on reality, we really have made no further mathematical progress in understanding the underpinning rules of creation. Our best evidence seems to be that such knowledge is prohibited (above & multiple lectures). By carefully applying our observations of the quantum world’s reality, Carlson has brilliantly described observations of quantum behavior that lead to an amazing array of technology. This course is a treasure.
Date published: 2020-12-17
Rated 5 out of 5 by from Easy to understand I don't understand why people are under the presumption that this is a college-level quantum mechanics course. Of course it isn't. It's purpose is to make the ideas of quantum mechanics known and understood and I must say, it does a phenomenal job doing so!
Date published: 2020-12-03
Rated 5 out of 5 by from Very clear! Very clear; make it easy to grasp a difficult subject for non-scientists.
Date published: 2020-10-28
Rated 5 out of 5 by from Really enjoyed this I felt I learned a lot and she made it accessible. It wasn't an easy course, but this is not an easy subject.
Date published: 2020-09-29
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Understanding the Quantum World
Course Trailer
Particle-Wave Duality
1: Particle-Wave Duality

Begin your journey into the quantum world by focusing on one of its most baffling features: the behavior of quantum entities as both particles and waves. Following her approach of presenting analogies over equations, Professor Carlson gives a handy way of visualizing this paradox. Then she takes you further into quantum weirdness by using a slinky to show how waves can be quantized.

25 min
Particles, Waves, and Interference Patterns
2: Particles, Waves, and Interference Patterns

Investigate one of the most famous demonstrations in physics: the double-slit experiment. See how electrons behave as both particles and waves when passing through two parallel slits in a plate and then striking a screen. Bizarrely, the wave properties disappear when the electrons are monitored as they pass through each slit, showing our inability to have complete information of a quantum state.

26 min
Observers Disturb What They Measure
3: Observers Disturb What They Measure

Consider what life would be like if quantum effects held at our everyday scale. For instance, there would be no trouble sitting in three chairs at once! Learn what happens when a particle in such a mixed state is forced by measurement to assume a definite position—a situation known as wave function collapse. This leads to the important quantum principle that observers disturb what they measure.

27 min
Bell’s Theorem and Schrödinger’s Cat
4: Bell’s Theorem and Schrödinger’s Cat

Ponder two celebrated and thought-provoking responses to the apparent incompatibility of quantum mechanics and classical physics. Bell’s theorem shows that attempts to reconcile the two systems are futile in a certain class of theories. Next, Schrödinger’s cat is a thought experiment implying that a cat could be both dead and alive if the standard interpretation of quantum mechanics holds.

28 min
Quantum Paradoxes and Interpretations
5: Quantum Paradoxes and Interpretations

Review the major theories proposed by physicists trying to make sense of the paradoxes of the quantum world. Look at the Copenhagen interpretation, Einstein’s realist view, the many worlds interpretation, quantum Bayesianism, non-local hidden variables, and other creative attempts to explain what is going on in a realm that seems to be governed by probability alone.

32 min
The Position-Momentum Uncertainty Relation
6: The Position-Momentum Uncertainty Relation

Heisenberg's uncertainty principle sets a fundamental limit on how much we can know about an object's position and momentum at the same time. Professor Carlson introduces this simple equation, showing how it explains why atoms have structure and come in the diverse forms of the periodic table of elements. Surprisingly, the stability of our everyday world rests on uncertainty at the quantum level.

30 min
Wave Quantization
7: Wave Quantization

Electrons don't just orbit the nucleus—they simultaneously exist as standing waves. Go deeper into what standing wave modes look like in one, two, and three dimensions, discovering that these shapes explain the quantization of energy states in an atom. As usual, Professor Carlson introduces useful analogies, including the standing waves produced in a vibrating drum head.

32 min
Quantum Wave Shapes and the Periodic Table
8: Quantum Wave Shapes and the Periodic Table

Focus on standing waves of electrons around nuclei, seeing how the periodic table of elements results from what electrons do naturally: fall into the lowest energy state given the total electric charge, existing electron population, and other features of an atom. Learn the Pauli exclusion principle and a handy mnemonic for remembering the terminology for atomic orbitals, such as 1s, 2p, 3d, etc.

30 min
Interference of Waves and Sloshing States
9: Interference of Waves and Sloshing States

Watch what happens when electrons are put into wave forms that differ from standing waves. Your goal is to understand why some of these superposition states are unstable. Professor Carlson notes that the sloshing of an electron back and forth in an unstable state causes it to act like an antenna, radiating away energy until it falls to a lower energy level.

29 min
Wave Shapes in Diamond and Graphene
10: Wave Shapes in Diamond and Graphene

What accounts for the dramatic difference between diamond and graphene (a sheet of graphite one atom thick), both of which are composed of pure carbon? Study the role of electrons in molecular bonds, applying your knowledge of electron standing waves. In carbon, such waves make possible several types of bonds, which in diamond and graphene result in remarkably different physical properties.

30 min
Harmonic Oscillators
11: Harmonic Oscillators

A clock pendulum is an example of a classical harmonic oscillator. Extend this concept to the atomic realm to see how quantum waves behave like harmonic oscillators. Then learn how quantum physics was born at the turn of the 20th century in Max Planck’s solution to a paradox in the classical picture of oscillating atoms. His conclusion was that the energies of oscillation had to be quantized.

32 min
The Energy-Time Uncertainty Relation
12: The Energy-Time Uncertainty Relation

Return to the Heisenberg uncertainty principle from Lecture 6 to see how quantum uncertainty also extends to energy and time. This has a startling implication for energy conservation, suggesting that short-lived “virtual” particles can pop into existence out of nothing—as long as they don’t stay around for long. Consider evidence for this phenomenon in the Lamb shift and Casimir effect.

29 min
Quantum Angular Momentum and Electron Spin
13: Quantum Angular Momentum and Electron Spin

Continue your investigation of the counterintuitive quantum world by contrasting angular momentum for planets and other classical objects with analogous phenomena in quantum particles. Cover the celebrated Stern–Gerlach experiment, which in the 1920s showed that spin is quantized for atoms and can only take on a very limited number of discrete values.

31 min
Quantum Orbital Angular Momentum
14: Quantum Orbital Angular Momentum

Having covered electron spin in the previous lecture, now turn to orbital angular momentum. Again, a phenomenon familiar in classical physics relating to planets has an analogue in the quantum domain—although with profound differences. This leads to a discussion of permanent magnets, which Professor Carlson calls “a piece of quantum physics that you can hold in your hand.”

33 min
Quantum Properties of Light
15: Quantum Properties of Light

Among Einstein’s insights was that light comes in discrete packets of energy called photons. Explore the photoelectric effect, which prompted Einstein’s discovery. See a do-it-yourself project that demonstrates the photoelectric effect. Close by surveying applications of the quantum theory of light to phenomena such as lasers, fluorescent dyes, photosynthesis, and vitamin D production in skin.

36 min
Atomic Transitions and Photons
16: Atomic Transitions and Photons

Dive deeper into the interactions of light with matter. Starting with a hydrogen atom, examine the changes in energy and angular momentum when an electron transitions from one orbital to another. See how the diverse possibilities create a “fingerprint” specific to every type of atom, and how this is the basis for spectroscopy, which can determine the composition of stars by analyzing their light.

28 min
Atomic Clocks and GPS
17: Atomic Clocks and GPS

Peer into the structure of a cesium atom to see what makes it ideal for measuring the length of a second and serving as the basis for atomic clocks. Then head into space to learn how GPS satellites use atomic clocks to triangulate positions on the ground. Finally, delve into Einstein’s special and general theories of relativity to understand the corrections that GPS must make to stay accurate.

29 min
Quantum Mechanics and Color Vision
18: Quantum Mechanics and Color Vision

Probe the quantum events that underlie color vision, discovering the role of the retinal molecule in detecting different frequencies of photons as they strike cone cells in the eye’s retina. Also investigate the source of color blindness, most common in men, as well as its inverse, tetrachromacy, which is the ability to see an extra channel of color information, possessed by some women.

29 min
A Quantum Explanation of Color
19: A Quantum Explanation of Color

Now turn to the sources of color in the world around us, from the yellow glow of sodium street lights to the brilliant red of a ruby pendant. Grasp the secret of the aurora, the difference between fluorescence and phosphorescence, and the reason neon dyes look brighter than their surroundings. It turns out that our entire experience of color is governed by the quantum world.

30 min
Quantum Tunneling
20: Quantum Tunneling

Anyone who makes use of a memory stick, a solid-state hard drive, or a smartphone relies on one of the most baffling aspects of the quantum world: quantum tunneling. Professor Carlson uses a roller coaster analogy, combined with your newly acquired insight into wave mechanics, to make this feat of quantum sorcery—the equivalent of walking through walls—perfectly logical.

32 min
Fermions and Bosons
21: Fermions and Bosons

Investigate why two pieces of matter cannot occupy the same space at the same time, reaching the conclusion that this is only true for fermions, which are particles with half-integer spin. The other class of particles, bosons, with integer spin, can be in the same place at the same time. Learn how this feature of bosons has been exploited in lasers and in superfluids such as liquid helium.

29 min
Spin Singlets and the EPR Paradox
22: Spin Singlets and the EPR Paradox

Study the most celebrated challenge to the Copenhagen interpretation of quantum mechanics: the paradox proposed by Albert Einstein and his collaborators Boris Podolsky and Nathan Rosen—later updated by David Bohm. Is quantum mechanics an incomplete theory due to hidden variables that guide the outcome of quantum interactions? Examine this idea and the experiments designed to test it.

29 min
Quantum Mechanics and Metals
23: Quantum Mechanics and Metals

Analyze how metals conduct electricity, discovering that, in a sense, electrons “surf” from one metal atom to the next on a quantum mechanical wave. Probe the causes of electrical resistance and why metals can never be perfect conductors. Finally, use the Pauli exclusion principle to understand the optimum distribution of electrons in the different quantum states of metal atoms.

31 min
24: Superconductivity

Close with one of Professor Carlson’s favorite topics: superconductivity. As noted in Lecture 23, when electrons flow through a metal, they lose energy to resistance. But this is not true of superconductors, whose amazing properties trace to the difference between bosons and fermions. Learn how quantum stability allows superconductors to conduct electricity with zero resistance, then step back and summarize the high points of your quantum tour.

35 min
Erica W. Carlson

The science that has illuminated the mysteries of the quantum world can also help us see our everyday world in a brand new way.


University of California, Los Angeles


Purdue University

About Erica W. Carlson

Erica W. Carlson is a 150th Anniversary Professor and Professor of Physics and Astronomy at Purdue University. She holds a BS in Physics from the California Institute of Technology and a Ph.D. in Physics from the University of California, Los Angeles (UCLA). A theoretical physicist, she researches electronic phase transitions in quantum materials. Widely recognized for her teaching and research, Professor Carlson received the prestigious Cottrell Scholar Award from the Research Corporation for Science Advancement, and she was elected a fellow of the American Physical Society. At UCLA, she won the teaching associate award from the Department of Physics and Astronomy. At Purdue, her honors include the university’s highest teaching prize, the Charles B. Murphy Outstanding Undergraduate Teaching Award, as well as the Ruth and Joel Spira Award for Excellence in Teaching (three times), and the College of Science Award for Outstanding Contributions to Undergraduate Teaching by an Assistant Professor. Professor Carlson has published dozens of research articles in peer-reviewed journals. She has also presented papers at many conferences and been invited to present talks worldwide, on four continents. Her early experiments with podcasting college science courses were featured on the front page of the Chicago Tribune. She is active in outreach, having given science presentations to the public and to students from preschool through high school.

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