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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.
The Many Hidden Worlds of Quantum Mechanics is rated 4.7 out of 5 by 18.
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Rated 5 out of 5 by 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 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 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
Rated 5 out of 5 by from Very clear explanations This is one of the better courses on Quantum Mechanics ! great job
Date published: 2024-02-21
Rated 5 out of 5 by from The Many Hidden Worlds of Quantum Mechanics Dr. Sean Carroll is mesmerizing in his explanation and delivery of the Many World field of Quantum Mechanics. I have learned from over 1200 The Great Courses/Wondrium courses. and Professor Carroll, like so many of TGCs eminent lecturers, such as Robert Greenberg, Rufus Fears (RIP), Alex Filenpinko, Hazen, Lincoln, etc, have a natural ability to deliver complex material in a clear, understandable manner. The speculative manner of the Many Worlds field, pushes the learner to conjure many interesting thought experiments. This is very refreshing look at fundamental quantum physics, its roots and forward looking considerations, relative to our natural world. Wonderful course and professor, which drives the learner to seek greater understanding of the field. Totally, worth the investment!
Date published: 2024-02-08
Rated 5 out of 5 by from An enjoyable but challenging course I found this to be a demanding course. I've read books by Sean Carroll and watched lectures given by him, so I had a good idea of what to expect in terms of his style of teaching. He didn't disappoint in that respect and, in this course, he demonstrated a natural, almost conversational, manner of presenting his material. As well as covering the history and basics of quantum mechanics, in the interests of open-mindedness, he also addressed alternative theories to the Many-Worlds interpretation, which seemed to me to be equally credible - or perhaps equally incredible! - as Many-Worlds. By the end I was far from convinced that he had made a strong case for Many-Worlds. Invariably, to support his case he used as examples isolated electrons, where he spoke about them being in a state of superposition and then, during a measurement process, becoming entangled with a large and complex external environment which can readily become disturbed by extraneous particles, such as photons, leading to decoherence and the branching of the wave function into Many-Worlds. I could follow this, but to my mind this doesn't address how Many-Worlds arise in 'real world' situations where the initial entanglement doesn't take place because of the inherent complexity of the system and the environment. However, I accept that this may well be because of my own limitations in understanding Many-Worlds, which Sean had to simplify for the purposes of this layperson's course, rather than because of an intrinsic weakness in the Many-Worlds interpretation. He also placed a lot of trust in the Schrödinger equation, saying that, in reality, the entire universe is one gigantic wave function but in practice, he argued, it's acceptable to assume that small units, such as subatomic particles, atoms and molecules, have their own wave functions. Indeed, this assumption is essential as the Schrödinger equation can only be solved for simple situations. However, as he admitted, it was open to question whether wave functions are real or whether they are simply mathematical tools which substitute for something else but which happen to give the right outcomes. Inevitably when dealing with a subject as vague as fundamental physics, the course was often concerned with metaphysics and philosophy such as when Sean was discussing consciousness and free will. This was interesting but as always when discussing these matters there were no definite answers, only more questions. Despite this being a challenging course, I found it very enjoyable and I doubt that anyone could have done a better job than Sean Carroll in presenting this subject matter. It would be great to sit down and have a conversation with him.
Date published: 2024-02-05
Rated 5 out of 5 by from Overall well presented though heavy going in parts so it is probably necessary to listen to a number of times
Date published: 2024-01-29
Rated 5 out of 5 by from A great course on the Many Worlds interpretation Great presentation of the Many Worlds interpretation and its subtle details. Well presented, as well. The only negative comment would be that Sean's face was filmed too close so you can see him reading the teleprompter which is distracting and diminishes the viewing experience - it's less "authentic" than an actual freely spoken presentation, but I understand why it's been done like this. Still, capturing from a little far out would lessen this.
Date published: 2024-01-12
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Overview

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.

About

Sean Carroll

We need to push on our understanding of cosmology, particle physics, gravity, not to mention how complexity and entropy evolve through time, and eventually you'll be able to really understand what our theories predict.

INSTITUTION

Johns Hopkins University

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.

By This Professor

The Many Hidden Worlds of Quantum Mechanics
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The Higgs Boson and Beyond
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The Many Hidden Worlds of Quantum Mechanics

Trailer

Why Suppose There’s More Than One World?

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
The Classical Physics World That Never Was

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
Quantum Worlds Start with Waves and Particles

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
A Wave Function to Describe Particles

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
Copenhagen Says the Wave Function Collapses

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
Is the Wave Function Real?

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
Uncertainty in Action with Spin and Qubits

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
Quantum Entanglement and Action at a Distance

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
Entanglement Leads to Many Worlds

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
Decoherence Explains Branching Worlds

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
How Entanglement Powers Quantum Computers

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
Too Many Worlds! Five Objections Answered

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
Testing the Many-Worlds Interpretation

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
Where Does Probability Come From?

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
Quashing Worlds with Wave Function Collapse

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
Blocking Worlds with Hidden Wave Variables

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
Mind before Matter in Quantum Theory

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
The Quantum Emergence of the World We See

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
The Challenge of Quantum Gravity

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
Space Emerges from Entanglement

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
The Quantum Emergence of Time

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
Free Will, Determinism, and Many-Worlds

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
What Happens to Ethics under Many-Worlds?

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
A Future Renaissance for Quantum Mechanics

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