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The Many Hidden Worlds of Quantum Mechanics
In a field known for startling ideas, the Many-Worlds Interpretation (MWI) of quantum mechanics may take the prize. It holds that parallel to our own world are a large number of other universes, almost identical to ours but with small variations. Copies of each of us inhabit a myriad of these worlds. But they are not us exactly; they share our past history, but they are different people who have unique futures. Although these realms are invisible and can’t communicate with each other, prominent physicists are convinced they must exist.
The Many Hidden Worlds of Quantum Mechanics is about why we should take the Many-Worlds Interpretation seriously, as arguably the best explanation of quantum mechanics, the science of matter and energy at the atomic and subatomic scales. In 24 fascinating lectures, Professor Sean Carroll of Johns Hopkins University guides listeners through the history, reasoning, and implications of this bold idea. He also covers alternate theories to Many-Worlds and unresolved questions in fundamental physics, making the course a thorough introduction to the current state of this exciting field.
Starting with classical physics, Professor Carroll explains how quantum theory overturned traditional ideas about matter and energy in the early 20th century. A consensus soon formed around a framework called the Copenhagen Interpretation, which rejected speculation about what was “really happening.� The Many-Worlds Interpretation in the 1950s was a reaction against this view, proposing that we take the basic equation of quantum mechanics seriously and go where it leads. It turns out it leads to Many-Worlds.
The course also covers quantum computing, quantum gravity, the resolution of quantum paradoxes, and speculation about whether human consciousness plays a central role in quantum experiments (Many-Worlds argues it doesn’t). Even die-hard skeptics of Many-Worlds will learn much from these lectures and will have their beliefs tested by a theory that is both mind-boggling and mathematically elegant.
The Many Hidden Worlds of Quantum Mechanics is about why we should take the Many-Worlds Interpretation seriously, as arguably the best explanation of quantum mechanics, the science of matter and energy at the atomic and subatomic scales. In 24 fascinating lectures, Professor Sean Carroll of Johns Hopkins University guides listeners through the history, reasoning, and implications of this bold idea. He also covers alternate theories to Many-Worlds and unresolved questions in fundamental physics, making the course a thorough introduction to the current state of this exciting field.
Starting with classical physics, Professor Carroll explains how quantum theory overturned traditional ideas about matter and energy in the early 20th century. A consensus soon formed around a framework called the Copenhagen Interpretation, which rejected speculation about what was “really happening.� The Many-Worlds Interpretation in the 1950s was a reaction against this view, proposing that we take the basic equation of quantum mechanics seriously and go where it leads. It turns out it leads to Many-Worlds.
The course also covers quantum computing, quantum gravity, the resolution of quantum paradoxes, and speculation about whether human consciousness plays a central role in quantum experiments (Many-Worlds argues it doesn’t). Even die-hard skeptics of Many-Worlds will learn much from these lectures and will have their beliefs tested by a theory that is both mind-boggling and mathematically elegant.
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Published November 24, 2023
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About the author
Sean Carroll
36Ìýbooks2,580ÌýfollowersSean Carroll is a physicist and philosopher at Johns Hopkins University. He received his Ph.D. from Harvard in 1993. His research focuses on spacetime, quantum mechanics, complexity, and emergence. His book The Particle at the End of the Universe won the prestigious Winton Prize for Science Books in 2013. Carroll lives in Baltimore with his wife, writer Jennifer Ouellette.
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Displaying 1 - 13 of 13 reviews
May 13, 2024
Largely discussed is the many-worlds interpretation (MWI) of quantum mechanics which states it holds a parallel to our own world and therein exists a vast number of other universes---practically identical to the one we are in now albeit with small variances. Apparently there are copies of us living in these other worlds. Our copies are not exact yet remain similar because they share our past history. Different people and futures. These worlds are invisible and can’t communicate with each other.
"You do not cause the wave function to branch by making a decision."
---Sean Carroll
"You do not cause the wave function to branch by making a decision."
---Sean Carroll
This entire review has been hidden because of spoilers.
April 14, 2025
Time isn't a straight line. It's a landscape—vast and silent—where multiple realities exist simultaneously, separated by the thinnest of veils.
In "The Many Hidden Worlds of Quantum Mechanics," Sean Carroll doesn't just explain quantum theory; he reveals it as the ultimate cinematic narrative, a story told in parallel dimensions where every possibility unfolds with mathematical precision. Reading his work, I was struck by how the equations of quantum mechanics resemble the architecture of dreams—structured yet boundless, precise yet fundamentally mysterious.
The book begins with deceptive simplicity, drawing you into the classical world we think we understand. Carroll establishes the "normal" before systematically deconstructing it, much like the opening sequence of a film that grounds you in reality before warping the foundations beneath your feet. His explanation of quantum superposition—the ability of particles to exist in multiple states simultaneously—reads like a masterclass in tension. The universe holds its breath, refusing to commit to a single outcome until observation forces its hand.
What Carroll accomplishes most brilliantly is translating the cold mathematics of quantum theory into something visceral. When he describes electrons as probability waves spreading across space, I don't merely understand the concept—I see it: ripples expanding across the darkness, each crest and trough a potential future, a path not yet chosen. The equations stop being symbols on a page and become a visual language expressing the universe's deepest structure.
His exploration of the Many-Worlds Interpretation particularly resonates with me. The notion that reality continuously branches, creating infinite parallel timelines where all possibilities exist—this isn't science fiction but the most straightforward reading of quantum equations. As Carroll guides us through this interpretation, the writing achieves a particular intensity. The words on the page seem to vibrate with potential meanings, with roads not taken that somehow exist alongside the path we perceive.
There's a haunting quality to quantum entanglement as Carroll describes it—two particles separated by vast distances, yet intimately connected, their properties linked in ways that defy our classical intuition. One particle somehow "knows" the state of its partner instantaneously, across any distance. This invisible connection between seemingly isolated entities mirrors the hidden relationships between characters or scenes that appear disconnected until their true relationship is revealed in the final act.
Carroll doesn't shy away from the philosophical implications. Quantum mechanics suggests that reality is not what it appears—that beneath the classical world we experience lies something fundamentally different, something that challenges our deepest intuitions about causality, locality, and identity. The book poses the ultimate question: if our perception of a single, definite reality is merely an approximation, an emergent property arising from quantum decoherence, what does this mean for concepts like choice and identity?
The prose achieves a remarkable balance between technical precision and evocative imagery. When discussing the measurement problem—the mysterious transition from quantum superposition to classical definiteness—Carroll writes with both scientific rigor and a sense of cosmic wonder. The mathematics is presented not as an obstacle but as a doorway into understanding.
In the final chapters, Carroll confronts the most profound implications of quantum theory. If the Many-Worlds Interpretation is correct, then every possible version of you exists somewhere in the quantum multiverse. Your identity becomes not a single narrative thread but a vast tapestry of possibilities—some threads vibrant and bold, others fading into darkness, but all equally real within the universal wave function.
What emerges is not just a scientific explanation but a new mythology for the modern age—a vision of reality as fundamentally plural, with our classical experience merely one room in an infinite mansion of possibility. Carroll's achievement is making this bizarre quantum landscape feel not alien but like a home we've always inhabited without realizing it.
The book closes not with answers but with a deeper mystery: how consciousness itself might relate to the quantum foundations of reality. Carroll approaches this question with appropriate caution, yet the implications linger like the final shot of a film that refuses easy resolution.
Reading "The Many Hidden Worlds of Quantum Mechanics" is like watching the universe fold in on itself, revealing hidden dimensions in what we thought was flat space. It leaves you seeing the ordinary world transformed—every decision point shimmering with quantum potential, every moment branching into countless worlds.
Time isn't just what your watch measures. It's what prevents everything from happening at once. And in the quantum realm Carroll illuminates, perhaps everything does.
In "The Many Hidden Worlds of Quantum Mechanics," Sean Carroll doesn't just explain quantum theory; he reveals it as the ultimate cinematic narrative, a story told in parallel dimensions where every possibility unfolds with mathematical precision. Reading his work, I was struck by how the equations of quantum mechanics resemble the architecture of dreams—structured yet boundless, precise yet fundamentally mysterious.
The book begins with deceptive simplicity, drawing you into the classical world we think we understand. Carroll establishes the "normal" before systematically deconstructing it, much like the opening sequence of a film that grounds you in reality before warping the foundations beneath your feet. His explanation of quantum superposition—the ability of particles to exist in multiple states simultaneously—reads like a masterclass in tension. The universe holds its breath, refusing to commit to a single outcome until observation forces its hand.
What Carroll accomplishes most brilliantly is translating the cold mathematics of quantum theory into something visceral. When he describes electrons as probability waves spreading across space, I don't merely understand the concept—I see it: ripples expanding across the darkness, each crest and trough a potential future, a path not yet chosen. The equations stop being symbols on a page and become a visual language expressing the universe's deepest structure.
His exploration of the Many-Worlds Interpretation particularly resonates with me. The notion that reality continuously branches, creating infinite parallel timelines where all possibilities exist—this isn't science fiction but the most straightforward reading of quantum equations. As Carroll guides us through this interpretation, the writing achieves a particular intensity. The words on the page seem to vibrate with potential meanings, with roads not taken that somehow exist alongside the path we perceive.
There's a haunting quality to quantum entanglement as Carroll describes it—two particles separated by vast distances, yet intimately connected, their properties linked in ways that defy our classical intuition. One particle somehow "knows" the state of its partner instantaneously, across any distance. This invisible connection between seemingly isolated entities mirrors the hidden relationships between characters or scenes that appear disconnected until their true relationship is revealed in the final act.
Carroll doesn't shy away from the philosophical implications. Quantum mechanics suggests that reality is not what it appears—that beneath the classical world we experience lies something fundamentally different, something that challenges our deepest intuitions about causality, locality, and identity. The book poses the ultimate question: if our perception of a single, definite reality is merely an approximation, an emergent property arising from quantum decoherence, what does this mean for concepts like choice and identity?
The prose achieves a remarkable balance between technical precision and evocative imagery. When discussing the measurement problem—the mysterious transition from quantum superposition to classical definiteness—Carroll writes with both scientific rigor and a sense of cosmic wonder. The mathematics is presented not as an obstacle but as a doorway into understanding.
In the final chapters, Carroll confronts the most profound implications of quantum theory. If the Many-Worlds Interpretation is correct, then every possible version of you exists somewhere in the quantum multiverse. Your identity becomes not a single narrative thread but a vast tapestry of possibilities—some threads vibrant and bold, others fading into darkness, but all equally real within the universal wave function.
What emerges is not just a scientific explanation but a new mythology for the modern age—a vision of reality as fundamentally plural, with our classical experience merely one room in an infinite mansion of possibility. Carroll's achievement is making this bizarre quantum landscape feel not alien but like a home we've always inhabited without realizing it.
The book closes not with answers but with a deeper mystery: how consciousness itself might relate to the quantum foundations of reality. Carroll approaches this question with appropriate caution, yet the implications linger like the final shot of a film that refuses easy resolution.
Reading "The Many Hidden Worlds of Quantum Mechanics" is like watching the universe fold in on itself, revealing hidden dimensions in what we thought was flat space. It leaves you seeing the ordinary world transformed—every decision point shimmering with quantum potential, every moment branching into countless worlds.
Time isn't just what your watch measures. It's what prevents everything from happening at once. And in the quantum realm Carroll illuminates, perhaps everything does.
May 5, 2024
Sean Carroll's course on quantum mechanics from The Great Courses is genuinely extraordinary. He explains complex topics with amazing clarity, providing a definitive yet balanced view that primarily champions the many-worlds interpretation (MWI) while giving fair treatment to other interpretations. As in all his works, the professor’s passion for MWI shines through, making a compelling case for its elegance and explanatory power. The best parts are the sections on alternative theories, presented fairly and adequately.
While I deeply enjoy the MWI defense, I find myself drawn to alternative explanations that might resolve the mysteries of the quantum realm without needing a constantly multiplying multitude of universes. My current line of thought is admittedly speculative and without any technical rigor � but at least something that sits better with me is the rest of this review as my takeaways. It relies on the often-overlooked concept of “recoherence� and its implications for our understanding of quantum phenomena.
My view effectively focuses on the dynamic interplay of decoherence and recoherence. Imagine fundamental particles possessing intrinsic properties, such as spin, represented by a "fuzzy pin." This pin has a definite orientation along one axis, signifying a decohered state for that specific property, while remaining fuzzy and indeterminate in all other directions—a superposition of possibilities waiting to be realized.
This fuzzy pin persists in its state until an "interaction" occurs, causing a perturbation that disrupts its current orientation and establishes a new axis of decoherence. Imagine a gentle nudge causing the pin to tilt, changing its alignment axis while the fuzziness now encompasses the previously definite direction. This dynamic process reflects the ever-evolving nature of quantum systems as they interact with their environment.
The crucial question then becomes: what triggers this "interaction" and subsequent shift in decoherence? Two main possibilities emerge:
a) Collective Influence: Similar to the pilot wave theory, the combined force of nearby wave functions, particularly within macroscopic objects where countless particles interact, creates a perturbation that nudges the fuzzy pin onto a new axis. This collective "push" from the environment influences the particle's state, causing it to decohere along a specific direction based on the net effect of surrounding influences.
b) Localized Interactions: Alternatively, the perturbation could arise from individual interactions between particles when they come within a highly close proximity, almost colliding. This suggests that decoherence is a more localized phenomenon occurring at the micro-level during close encounters between particles. The probability of such close encounters increases significantly within macroscopic objects due to the sheer number of particles involved, leading to a higher likelihood of decoherence along a specific axis relevant to the measurement context.
This refined perspective aligns with elements of both pilot wave theory and other interpretations that emphasize the role of interactions in shaping quantum behavior. It suggests that decoherence is not a one-time event but rather a dynamic process where particles continuously shift between definite and indeterminate states based on their interactions with the environment. The fuzzy pin analogy captures this fluidity, with its axis of decoherence constantly adapting to the influences it encounters.
This interpretation, which ties with what we observe in sciences elsewhere, is not just a mere speculation. It may contain hidden variables or sub-theories, or alternatively, it could be one that should be falsifiable fairly quickly in all various forms, providing a solid foundation for further exploration.
Back to the course, it is a valuable resource for anyone interested in the field.
While I deeply enjoy the MWI defense, I find myself drawn to alternative explanations that might resolve the mysteries of the quantum realm without needing a constantly multiplying multitude of universes. My current line of thought is admittedly speculative and without any technical rigor � but at least something that sits better with me is the rest of this review as my takeaways. It relies on the often-overlooked concept of “recoherence� and its implications for our understanding of quantum phenomena.
My view effectively focuses on the dynamic interplay of decoherence and recoherence. Imagine fundamental particles possessing intrinsic properties, such as spin, represented by a "fuzzy pin." This pin has a definite orientation along one axis, signifying a decohered state for that specific property, while remaining fuzzy and indeterminate in all other directions—a superposition of possibilities waiting to be realized.
This fuzzy pin persists in its state until an "interaction" occurs, causing a perturbation that disrupts its current orientation and establishes a new axis of decoherence. Imagine a gentle nudge causing the pin to tilt, changing its alignment axis while the fuzziness now encompasses the previously definite direction. This dynamic process reflects the ever-evolving nature of quantum systems as they interact with their environment.
The crucial question then becomes: what triggers this "interaction" and subsequent shift in decoherence? Two main possibilities emerge:
a) Collective Influence: Similar to the pilot wave theory, the combined force of nearby wave functions, particularly within macroscopic objects where countless particles interact, creates a perturbation that nudges the fuzzy pin onto a new axis. This collective "push" from the environment influences the particle's state, causing it to decohere along a specific direction based on the net effect of surrounding influences.
b) Localized Interactions: Alternatively, the perturbation could arise from individual interactions between particles when they come within a highly close proximity, almost colliding. This suggests that decoherence is a more localized phenomenon occurring at the micro-level during close encounters between particles. The probability of such close encounters increases significantly within macroscopic objects due to the sheer number of particles involved, leading to a higher likelihood of decoherence along a specific axis relevant to the measurement context.
This refined perspective aligns with elements of both pilot wave theory and other interpretations that emphasize the role of interactions in shaping quantum behavior. It suggests that decoherence is not a one-time event but rather a dynamic process where particles continuously shift between definite and indeterminate states based on their interactions with the environment. The fuzzy pin analogy captures this fluidity, with its axis of decoherence constantly adapting to the influences it encounters.
This interpretation, which ties with what we observe in sciences elsewhere, is not just a mere speculation. It may contain hidden variables or sub-theories, or alternatively, it could be one that should be falsifiable fairly quickly in all various forms, providing a solid foundation for further exploration.
Back to the course, it is a valuable resource for anyone interested in the field.
November 22, 2024
It hit me halfway through this lecture series that Sean Carroll sounds a lot like the comedian John Mulaney when he is talking. Maybe that's why I always love to hear his voice -- he always sounds so happy to be lecturing about theortical physics and yet has a bit of underlying self-deprecation that makes you want to be on his side. And on his side I was as I listened to him explain the many worlds interpretation of quantum physics.
Carroll does a great job explaining why the many worlds intepretation is not only the most reasonable of the current popular quantum theories out there, but why it also is the simplest because it doesn't require anything above and beyond the standard Schrödinger wave equation. It just requires that we can deal with the fact that there are a bunch of "other worlds" out there that satisfy every value of the wave equation. Enlightening and fascinating. But more than that, Carroll does a great job giving us a survey of all the other theories and ideas out there today. After listening to this course, I feel like I (barely) have a grasp of the scope of the current opinions, and, going forward, I feel like I will have a better personal quantum theory schema to hook in other ideas as I learn about them. Thanks Sean.
Carroll does a great job explaining why the many worlds intepretation is not only the most reasonable of the current popular quantum theories out there, but why it also is the simplest because it doesn't require anything above and beyond the standard Schrödinger wave equation. It just requires that we can deal with the fact that there are a bunch of "other worlds" out there that satisfy every value of the wave equation. Enlightening and fascinating. But more than that, Carroll does a great job giving us a survey of all the other theories and ideas out there today. After listening to this course, I feel like I (barely) have a grasp of the scope of the current opinions, and, going forward, I feel like I will have a better personal quantum theory schema to hook in other ideas as I learn about them. Thanks Sean.
April 2, 2024
The Many Hidden Worlds of Quantum Mechanics" by Sean Carroll serves as an intricate exploration of quantum mechanics, approached with Carroll's commendable humility and expertise. While Carroll advocates for the many-worlds interpretation, presenting thought-provoking arguments, readers may find themselves contemplating simpler alternatives to this complex quantum conundrum. Regardless, the book is a valuable contribution to the field, inviting both assent and thoughtful challenge, and it stands as a testament to the ongoing, fascinating dialogue surrounding the foundations of quantum physics.
Reflecting on this, the book does more than just educate; it stimulates critical thinking and encourages the pursuit of simpler, perhaps more elegant theories in quantum mechanics that are yet to be discovered. It's a compelling read for those who enjoy rigorous scientific discourse wrapped in accessibility.
Reflecting on this, the book does more than just educate; it stimulates critical thinking and encourages the pursuit of simpler, perhaps more elegant theories in quantum mechanics that are yet to be discovered. It's a compelling read for those who enjoy rigorous scientific discourse wrapped in accessibility.
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June 24, 2024Great book, thought-provoking and enlightening. Are time and space emergent phenomena, i.e. not fundamental? At what point do worlds split, as posited by this theory?
Many interesting concepts elucidated which you might have heard of, but never had time to wrap your head around: quantum entanglement, decoherence, etc. Sean C. even spends some time on compatabilism, i.e. the tension between determinism and perceived free will as basis for morality.
Many interesting concepts elucidated which you might have heard of, but never had time to wrap your head around: quantum entanglement, decoherence, etc. Sean C. even spends some time on compatabilism, i.e. the tension between determinism and perceived free will as basis for morality.
May 27, 2024
As usual Sean Carroll delivers. While I don’t ascribe to the many worlds interpretation of quantum mechanics, there’s plenty of other fun stuff here. While Dr Carroll goes to some lengths to make this complex subject approachable, this is not a light treatment.
August 21, 2024
Fantastic overview of this particular branch of Quantum Physics by Professor Sean Carroll. It is does a great job at considering other branches and interpretations as well.
February 17, 2025
Over my head at many points but fascinating ideas
April 29, 2025
From what I’ve gathered there should be a branch of myself somewhere that understood this
August 22, 2024
This was a great book as an introductory to Quantum Mechanics, and the Hidden Worlds theory. It is not so deep in the weeds of the science and math, that the subject is inapproachable. But it does go deep enough that you feel like you're learning something new, and have a general understanding of the history and current work being done in this area.
September 26, 2024
Definitely read this before his current book "The Biggest Ideas in the Universe: Quanta and Fields" unless Physics is your day job. It builds from the basics up to the cutting edge.
November 30, 2024
Difficult but mind-blowing.
I had to listen to this audiobook course twice, sometimes replaying specific sections, to appreciate all implementations. This is not my first contact with physics and I have been an amateur reader about quantum mechanics, even though I ignore the underlying maths.
Before listening to this course I barely knew about Everett interpretation and never really understood what it was about.
After listening to this course I can say the "many worlds" is the only interpretation that makes some sense to me.
The reader does an excellent job with explaining. he's also part of the minority of physicists supporting this interpretation which have interesting (upsetting) philosophical implications
I had to listen to this audiobook course twice, sometimes replaying specific sections, to appreciate all implementations. This is not my first contact with physics and I have been an amateur reader about quantum mechanics, even though I ignore the underlying maths.
Before listening to this course I barely knew about Everett interpretation and never really understood what it was about.
After listening to this course I can say the "many worlds" is the only interpretation that makes some sense to me.
The reader does an excellent job with explaining. he's also part of the minority of physicists supporting this interpretation which have interesting (upsetting) philosophical implications
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