Taught by Professor Sean Carroll of Johns Hopkins University, this course explores the Many-Worlds Interpretation (MWI) of quantum mechanics, which proposes that there are a limitless number of universes caused by the branching of different realities at the quantum level. These universes include countless versions of ourselves living out different futures. Consider the pros and cons of this bold theory.
The Many Hidden Worlds of Quantum Mechanics
One universe is not enough. Learn about the Many-Worlds Interpretation of quantum mechanics in this exciting course taught by a renowned expert.
Rated 5 out of
5
by
BarbM from
So glad I signed up.
I've spent 6 months on this course and am very glad I did. I'm smart, but no science background and I just wanted to understand more about quantum mechanics. Sean Carroll was excellent in the way he explained what is a very complex subject. I'm not an expert now, but I understand so much more, and am intrigued enough to further study the subject.
Date published: 2024-11-01
Rated 5 out of
5
by
A Life Long Learner from
EXCELLENT AND PRESENTED WITH SKILL
EXCELLENT AND PRESENTED WITH SKILL - Sean Carroll has an excellent teaching skill and is able to identify which areas of a topic that can cause difficulties with his students then breaking down those areas and expanding their teaching time to make sure it is understood. Not seen this skill taken to this level before ....... it's impressive!
Date published: 2024-10-30
Rated 5 out of
5
by
Habiscus Too from
Awesome course, but with fundamental question
I am officially over halfway through course and loving it. The Bottom Line is that this is the most complete and understandable explication of quantum mechanics that I have encountered to date, to the extent that I can actually understand it. I will have to watch the course multiple times and/or read the course transcript to really get it. Dr. Carroll is his usual affable, entertaining self.
HOWEVER…
At the risk of demonstrating to the denizens of the Great Courses Universe just how unenlightened I am, I will hazard a question that hopefully some smart person can answer.
I keep getting hung up on the course’s visual representation of the single particle wave function. It makes me doubt the degree to which I am understanding what Dr. Carroll is trying to impart.
The course repeatedly depicts the single particle wave function with an X-Y coordinate plane with the X-axis labeled as “position” (or “momentum” as introduced in lesson 6) and the Y-axis labeled as “wave function”. The Y-axis label doesn’t include any values, implicitly telling me that the X-axis intersects the Y-axis at its “zero” value.
Based on my understanding gained from the course, I think the Y-axis should actually be labeled as “probability”, not as “wave function”, and the curve should then be entirely above the zero value of the Y-axis.
The single particle wave function curve the course depicts is sinusoidal in shape and symmetric across the Y-axis, thus the area under the curve sums to zero (again, assuming the X-axis intersects the Y-axis at its zero value), when it really should sum to one... at least that is what I believe is supposed to be the case.
If you are going to represent the wave function with an X-Y plane, shouldn’t the Y-axis be labeled “probability” and the X-axis would be labeled as “position” or “momentum”? The curve would then be entirely above the X-axis and extend asymptotically towards both ends of the X-axis. In such a case the “zero” of the X-axis when the X-axis is “momentum” would represent the “particle’s” velocity being zero, and the “zero” of the X-axis when the X-axis is “position” would represent some arbitrary point in space.
Is this correct? I have to know, because if it isn't then I am misunderstanding what quantum mechanics is saying at its most fundamental level.
Any help would be appreciated.
Date published: 2024-08-11
Rated 5 out of
5
by
Alan_R from
Really enjoyed these thought provoking talks
Although I am not wholly convinced by many worlds, I did like that the author presented both many worlds and alternatives objectively and conceded that we don't have experimental verification for either it or its alternatives.
I particularly liked the explanation of how many-worlds supported the idea of emergent space thorough entanglement of fields suggesting a metric on space-time that in the limit might yield Einstein's equation. The explanation of emergent time, I found less convincing (though still interesting) since it started by calling a sub-system of the Hilbert Space of the universe, the clock which seemed to me a difficult prior assumption if you want time to be emergent.
Although he took on many of the objections to many-worlds, I didn't hear his take on how he sees the existence of these many worlds in space time. If you accept the standard idea that fermion fields take up space then on the face of it, there is nowhere space-time to put all of these parallel realities. I would have liked to have heard his rebuttal of that.
On the other side of the argument, I think David Deutsch's arguments around quantum computing are intriguing but didn't feature strongly. If you think of a computation as a transformation of matter from one state (the input) to another state (the output) in a finite number of steps then things like Shor's algorithm for factorising large primes, which requires more steps than there are particles in the observable universe are very hard to explain and Deutsch's explanation of parallel computation across the multiple universes of many worlds at least in principle offers an answer that other models struggle to provide. But these are my subjective preferences or questions and don't detract from the journey the talks offer.
Date published: 2024-07-24
Rated 5 out of
5
by
outbackaussie from
Many worlds
I enjoy the courses of Sean Carroll
this one wandeed a bit but was interesting
encourage me to read further into Hugh Everett III
he made a great case for, and made it sound obvious
(which it almost certainly is not)
highly recommeded - as are all his courses
Date published: 2024-06-20
Rated 5 out of
5
by
JPM54 from
Fascinating course
This is not an easy course. Professor Carroll introduces several controversial topics which, by his own admission, are not well understood. Some of the concepts seem perceptibly simple but as the course progresses one finds out that they are anything but simple. This course would be worthwhile watching a second time. I am a fan of Sean Carroll; I enjoy his approach to lecturing very much. His courses are real assets for Wondrium/The Great Courses.
Date published: 2024-06-14
Rated 3 out of
5
by
leadsled from
Can anyone save us from this nonsense?
I have been a long-time fan of Sean Carroll, and have bought several of his books and DVDs, most notably the DVDs produced by The Great Courses. He has a great talent for explaining difficult concepts, especially those involving quantum mechanics. However, his most recent series of lectures entitled "The Many Hidden Worlds of Quantum Mechanics" is a bridge too far. Way too far, in fact. The notion that there are a limitless number of universes caused by the branching of different realities strikes me as science fiction rather than science. I finally pulled the plug at lecture 9. Is there anyone who can save us from this multiverse nonsense?
Date published: 2024-05-27
Rated 5 out of
5
by
TommyBVA from
Great Course
I'll echo all the good things stated in other reviews, and don't disagree with some of the negative. Sean Carroll has a tremendous gift of explaining complex physics so that a "layman" can understand. Rather than be offended by the science vs. philosophy aspect, I find the "entanglement" interesting.
I found it to be an interesting topic, and his explanations of its development were more than adequate to follow the train of thought.
I highly recommend the course.
Date published: 2024-02-22
Overview
About
Sean Carroll is the Homewood Professor of Natural Philosophy at Johns Hopkins University and both a member of the Fractal Faculty and an External Professor at the Santa Fe Institute. He received his PhD in Astrophysics from Harvard University. He is the author of several books, including Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime, and the host of the weekly Mindscape podcast. He has been awarded prizes and fellowships by the National Science Foundation, NASA, and the Guggenheim Foundation, among others.
Trailer
01: Why Suppose There’s More Than One World?
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.
32 min
02: The Classical Physics World That Never Was
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.
31 min
03: Quantum Worlds Start with Waves and Particles
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 central tenets of quantum mechanics.
29 min
04: A Wave Function to Describe Particles
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.
27 min
05: Copenhagen Says the Wave Function Collapses
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.
28 min
06: Is the Wave Function Real?
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.
31 min
07: Uncertainty in Action with Spin and Qubits
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.
29 min
08: Quantum Entanglement and Action at a Distance
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. In his controversial “EPR” paper, Einstein tried to use this feature to argue that quantum mechanics must be incomplete.
33 min
09: Entanglement Leads to Many Worlds
Use the 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.
31 min
10: Decoherence Explains Branching Worlds
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.
30 min
11: How Entanglement Powers Quantum Computers
Many-Worlds theorist David Deutsch helped pioneer quantum computing, which he argues is an outgrowth on the Many-Worlds Interpretation. Investigate the principles behind quantum computing, comparing it to classical computing. Discover that the big difference is the architecture of logic gates. See how quantum computers can surmount this obstacle and excel at certain types of calculations.
31 min
12: Too Many Worlds! Five Objections Answered
The Many-Worlds view seems to defy common sense. Why can’t we see the other worlds? And don’t they violate the laws of physics and other rules of nature? Professor Carroll answers five major objections, concerning the philosophical concept known as Occam’s Razor, the problem of time asymmetry, the possibility of infinity, plus scruples about immortality and energy conservation.
31 min
13: Testing the Many-Worlds Interpretation
Address another objection to the Many-Worlds Interpretation: its testability. This refers to philosopher Karl Popper’s famous falsifiability criterion, which discounts any theory that can’t in principle be proven false. The proliferation of worlds that can’t ever be observed might seem to qualify Many-Worlds as unfalsifiable, but Professor Carroll shows that it is testable where it counts.
28 min
14: Where Does Probability Come From?
Yet another hurdle for Many-Worlds is the origin and nature of probability. The Copenhagen version of quantum mechanics is fundamentally probabilistic, rather than deterministic. This is a key feature in its success. By contrast, Many-Worlds is deterministic. We can derive an understanding of probability by thinking about where we are in the quantum wave function.
32 min
15: Quashing Worlds with Wave Function Collapse
Given the mind-boggling implications of Many-Worlds, many physicists have sought plausible alternatives. In this lecture, consider the possibility of altering the Schrödinger equation—the jumping-off point for Many-Worlds. Investigate two proposals that try this tactic: GRW (named after its inventors, Ghirardi, Rimini, and Weber) and CSL (Continuous Spontaneous Localization) theory.
28 min
16: Blocking Worlds with Hidden Wave Variables
Does the wave function tell the whole story? Explore the hidden variable theory, devised by Louis de Broglie and refined by David Bohm. According to this view, particles are guided by pilot waves constructed from the wave function. The “hidden variables” are the precise positions of particles, which are being guided by the pilot waves. Learn why some critics call the idea “Many-Worlds in denial.”
30 min
17: Mind before Matter in Quantum Theory
Since quantum mechanics and consciousness are both mysterious, could they be connected in some way? Examine several arguments that relate quantum phenomena to the involvement of conscious observers. The Copenhagen Interpretation is particularly open to such speculations. Also, look at Quantum Bayesianism, or QBism, which sidesteps quantum paradoxes by dispensing with the idea of objective reality.
29 min
18: The Quantum Emergence of the World We See
How does the structure of observed reality emerge from the wave function in Many-Worlds? In other words, where do the worlds come from? This question relates to the “preferred basis” problem that attempts to link the quantum realm to everyday macroscopic objects. See how Schrödinger’s clever thought experiment involving a cat provides a conceptual tool for solving this puzzle.
31 min
19: The Challenge of Quantum Gravity
Quantum theory accounts for a remarkable array of particles and forces—but not gravity. Learn why constructing a successful theory of quantum gravity has vexed physicists for nearly a century. Professor Carroll lays the groundwork for discussing the Many-Worlds perspective on gravity by focusing on two popular alternative theories: string theory and loop quantum gravity.
33 min
20: Space Emerges from Entanglement
Starting with the basic ingredients of quantum theory—wave functions, Schrödinger’s equation, and entanglement—and following the Many-Worlds approach, probe this question: What circumstances lead to emergent branches of the wave function that look like matter moving in curved spacetime—that is, in gravitational fields? Find that gravity may be a natural consequence of quantum mechanics.
30 min
21: The Quantum Emergence of Time
As space might be an emergent property of quantum entanglement, could the same be true of time? Divide a wave function into subsystems and watch how the rest of the universe becomes entangled in a manner that can be interpreted as time passing. Along the way, learn the ideas behind the Wheeler-DeWitt equation, which helped define the “problem of time.”
28 min
22: Free Will, Determinism, and Many-Worlds
Get philosophical by probing a pair of profound questions that arise from the far-out implications of Many-Worlds. Are multiple branching worlds caused by our decisions? Is human free will possible, especially in light of the deterministic nature of Many-Worlds? Professor Carroll analyzes the way the macroscopic world of human thought and action interact with the quantum realm.
28 min
23: What Happens to Ethics under Many-Worlds?
A theory in which every moral act entails an immoral one taking place in a branching universe is rife with ethical quandaries. Now, consider whether you could be moral in each of the universes of a Many-Worlds scenario—or if that’s even possible. One stumbling block is imagining that the version of you that took a branching path is actually you. You may share a past, but the two of you are really different people.
27 min
24: A Future Renaissance for Quantum Mechanics
Many-Worlds and competing theories on the foundations of quantum mechanics may seem essential for our understanding of reality, but they were long ignored by no-nonsense practicing physicists. Close the course by witnessing how the tide is turning, as it becomes increasingly clear that the foundational issues are likely the key to unlocking the outstanding mysteries of the cosmos.
31 min
