Acknowledgements
Introduction
Prologue: Nothing is Real

━Part 1 Quantum
Chapter 1 Light
Wave or Particle? │The Complete Triumph of Wave Theory
Chapter 2 Atoms
19th-century atomic theory│Einstein's atoms│electrons│ions│X-rays│radioactivity│inside the atom
Chapter 3 Light and Atoms
Finding Clues in Black Bodies│An Unwelcome Revolution│What is the Identity of h?│Einstein, Light, and Quantums
Chapter 4 Bohr's Atom
The Jumping Electron│The Internal Structure of the Hydrogen Atom Finally Revealed│Probabilistic Elements: God's Dice│Atomic Perspectives│Chemistry Standing Tall with Atomic Models

━Part 2 Quantum Mechanics
Chapter 5: Photons and Electrons
Particles of Light│Wave-Particle Duality│Electron Waves│Breakup with the Past│Pauli's Exclusion Principle│Where to Look Next?
Chapter 6 Matrices and Waves
Finding a breakthrough on Heligoland│Quantum mathematics│Schrödinger's theory│Back to the past│Quantum cooking
Chapter 7: Cooking with Quantum
Antimatter│Inside the Nucleus│Lasers and Masers│The Micro Era│Superconductors│Life

━Part 3 Beyond Quantum Mechanics
Chapter 8 Probability and Uncertainty
The Meaning of Uncertainty│The Copenhagen Interpretation│The Double-Slit Experiment│Collapsed Waves│The Complementarity Rule
Chapter 9 Paradox and Probability
A Clock in a Box│The EPR Paradox│Time Travel│Einstein's Time│There Is 'Free' in the World│Schrödinger's Cat│Participatory Universe
Chapter 10 Bell's Inequality
Spin Paradox | The Riddle of Polarization | Bell's Experiment | Proof | The Meaning of Proof | Confirmation and Application
Chapter 11: Multiverse
Who Observes the Observer? │ Two Realities │ Beyond Science Fiction │ Beyond Einstein │ Revisiting │ Beyond Everett │ Our Special World

Epilogue: Unfinished Tasks
Twisted Spacetime│Collapsed Symmetry│Supergravity│Is the Universe a Vacuum Fluctuation?│Inflation and the Universe
Translator's Note
Americas
References
Search

“Once you open it, you can never put it down!” _Isaac Asimov
"The best book to popularize physics before Stephen Hawking's A Brief History of Time" - Spectator Book Club
“Sophisticated yet mysterious, as beautiful as poetry and as exciting as a novel.” —The Sunday Times
★★★★★

The masterpiece of John Gribbin, the 'best science writer'
Published in 1984, it was the first popular book on quantum mechanics and remains an excellent introduction to the subject.

When it comes to 'quantum mechanics', many people probably think of 'Schrödinger's cat'.
So how many people can truly understand and explain the content of the "Schrödinger's Cat" experiment and its symbolism in quantum mechanics? "In Search of Schrödinger's Cat" is the masterpiece of John Gribbin, a top science writer selected by Nature and The Spectator and recipient of the American Association for the Advancement of Science's Distinguished Service Award for his contributions to the popularization of science. It is a classic of quantum mechanics that readers have consistently sought out since its first publication in 1984.

In this book, the author shows how the quantum world differs from the real world through a quantum entity called 'Schrödinger's cat'.
In the quantum world, the 'laws of physics' we experience on a daily basis no longer apply, and all events are determined by probability.
By following John Gribbin's story about what fate awaits the cat in the box, we can arrive at a new interpretation that embraces the traditional interpretation of quantum mechanics while also transcending it, understanding what a "cat that is dead while alive" means.


Above all, he generously shows off his skills as a 'top science writer' by explaining to the public what 'quantum mechanics' is.
This book is a reasonably detailed and moderately difficult introduction to quantum mechanics.
John Gribbin doesn't try to explain everything, but tells us just enough to understand quantum mechanics.
If we overcome the barrier of unfamiliar physics terms, the quantum world, the 'real reality' that exists beyond our imagination, awaits us.
The truth hidden in the quantum world is more absurd and mysterious than any novel in this world.
No wonder physicist Niels Bohr said, “If you are not shocked by quantum theory, you do not understand it properly.”
The world of quantum mechanics is certainly daunting, but as you turn the pages, following John Gribbin's masterful explanations and apt analogies, even if you don't fully understand quantum mechanics, you'll gain a solid understanding of how modern science views the world.



From the birth of quantum mechanics to its completion, a 100-year history of quantum theory.
─The story of the 20th-century genius physicists who opened the door to the quantum revolution.

From the perspective of Newton's classical mechanics, which has dominated the world, if the positions and velocities of all particles in the universe are known, their futures are also perfectly determined through the laws of motion.
This also means that the future of the universe has already been decided.
As scientists began to realize that there was no room for human free will or chance in the 'deterministic universe' created by Newton's classical mechanics, they began to move toward a new physics of the 20th century.


Part 1, "Quantum," begins with the debate over the wave and particle theories of light, and covers the new discoveries of the period when the concept of "quantum" was defined through Planck's research, which found clues in the internal structure of atoms and black bodies, and Bohr's atomic model, and the basic concepts for understanding quantum mechanics.


Part 2, “Quantum Mechanics,” tells the story of the scientific community’s break with classical physics after the particle theory of light was accepted and de Broglie first proposed the duality of matter, accepting that “all particles, including photons and electrons, are waves, and all waves are particles.”
Although a great deal of research was being actively pursued around that time, quantum theory in 1925 was a messy mess of various hypotheses and computational problems.
However, after experiencing extreme confusion, it was only a few months later that quantum mechanics became established as an orthodox theory of physics, with Heisenberg's idea that 'only that which can be observed through experiment can be a physical object' and Dirac's research realizing that the equations of quantum mechanics have the same structure as the equations of classical mechanics, allowing for an accurate description of the movement of atoms.


John Gribbin, especially in Part 3, “Beyond Quantum Mechanics,” laments the fact that although Heisenberg’s uncertainty principle was derived from the fundamental equations of quantum mechanics, most physicists start with the uncertainty principle when introducing quantum mechanics to the public, leaving people with no opportunity to learn the fundamental equations, and narrowly understanding the uncertainty principle as a “limitation of observation” rather than a fundamental property of the universe.
Part 3 focuses on the 'second generation of quantum mechanics' who demonstrated their capabilities after the basic concepts and laws of quantum mechanics were established.
This paper introduces the EPR paradox, Bell's floating theory, and the many-worlds interpretation through advanced discussions of attacks and defenses against the Copenhagen interpretation.


Why do we need to know quantum mechanics?
─The greatest achievement of science, all science is explained by quantum mechanics!

Even people who show great interest and affection for the academic discipline of science tend to turn their heads away from the field of quantum mechanics.
This may be because it is not a theory that can be expected to have an obvious explanation, such as 'stones fall from above'.
From a quantum perspective, there could also be a world where rocks 'suddenly rise from below'.
Even phenomena that are thought to be impossible according to the laws of physics in the real world can occur if the probability of their occurrence is not zero.
It's just that the probability is so low that we don't encounter it in our daily lives.
The reason quantum mechanics feels unfamiliar is because the results predicted by the theory can deviate greatly from our common sense.
So, to enter the world of quantum mechanics, you need to forget all conventional wisdom and be prepared to “accept anything.”


Why is it necessary to make such mental preparations and strive to understand the quantum world? Quantum theory is the study of how particles in the microscopic world move.
Everything in this world is made up of particles.
Therefore, it is no exaggeration to say that quantum mechanics is not simply a branch of science, but a theory that underpins all of modern science.
Without quantum mechanics, chemistry would still be stuck in the Dark Ages, and fields like molecular biology would not even exist.
Those who understand quantum mechanics can experience a different dimension, where they can sense things that are invisible to the eye, without stopping in the world they have seen with their eyes.
Just as everyone feels a thirst for 'truth' at least once in their lives, a theory that can explain everything with a single principle is fascinating.
Quantum mechanics is a core subject of modern society that influences not only science and technology, but also philosophy, literature, and art.
After reading this book, you will realize how simple and beautiful the best science can be.



Why In Search of Schrödinger's Cat is the Best Introductory Book
─A narrative flow and clear metaphors optimized for understanding quantum mechanics.

To introduce unfamiliar concepts to the public in a friendly manner, you need to know where people are vulnerable.
John Gribbin is the writer who sees that point better than anyone else.
He found that people had difficulty connecting the concepts organically, even though they understood each concept fragmentarily.
It takes a long time for a new theory to be accepted in academia.
In the process, numerous scholars and formulas emerge.
Some hypotheses are adopted as major theories only after a long time after they are announced, and many are used only as hints and then buried.
The author explains how each concept gained precision, who influenced whom, and how new theories that complement previous hypotheses were developed, in a structure that best suits readers' understanding of quantum mechanics.
This is where John Gribbin excels as a science writer.


“Most textbooks present quantum mechanics as a step-by-step progression, but new theories and new discoveries did not always appear in time.
However, if I list everything in the order of discovery, the logic will get mixed up, so I think I will have to adjust the order in this book as well.
The best way to do this is to go over the basic concepts related to quantum mechanics one by one before explaining it.” _Page 127

He is also a writer who excels at explaining scientific concepts using everyday analogies.
He likens the fact that energy exists in chunks of specific sizes to a bank ATM only dispensing money in five-pound increments, and the difference between fermions and bosons to the audience sitting in order of the highest and lowest priced seats at a concert, and the audience running to the front of the stage to the sound of an exciting song.
This analogy allows readers without a strong physics background to intuitively understand unfamiliar concepts.

“What is the difference between a fermion and a boson? …… No one will be satisfied with this explanation without knowing the nature of spin, so let’s try a more realistic analogy.
A while ago I went to see a play starring the comedian Spike Milligan.
Before the curtain even rose, Milligan walked out onto the stage and spoke to the audience.
“All the best seats are empty.
I guess our PR staff couldn't find anyone willing to pay a lot of money to see my play.
“But it would be a shame to leave them empty, so please move everyone to the front seats.” As soon as he finished speaking, the first class seats that had been empty were filled with audience members in an instant, and the back seats, where tickets were the cheapest, were left empty.
This is exactly how fermions behave.
Only one person can sit in each seat, and these are filled sequentially starting from the front seat.” _Pages 144-145


Quantum mechanics after 1984, supplemented by release
How modern science understands the world: The power of quantum thinking!

Thirty-six years have passed since the publication of In Search of Schrödinger's Cat, but in fact, quantum mechanics has not changed much.
However, the biggest changes discovered in the meantime are the discovery of 'string theory' and the Higgs particle.'
Superstring theory, which emerged as an alternative to the standard model of quantum mechanics, shocked quantum physicists who adhered to tradition, and the Higgs boson, discovered at the European Organization for Nuclear Research in 2012, gave wings to the standard model of quantum mechanics.
These two contents were supplemented through the commentary by Park Byeong-cheol, who translated this book.

If you finish reading this book and don't fully understand quantum mechanics, don't be discouraged.
It is not the reader's problem or the book's problem, but the strange and bizarre nature of the discipline called 'quantum mechanics'.

But two things I can promise you for sure:
One is that after reading this book, you will be able to accurately explain the situation in which Schrödinger's cat was placed inside the box. The other is that you will realize how to understand the real world through quantum thinking, and you will be able to look at the world with a different sense than before.