Introduction: Is Our Universe Unique?

1.
The Boundary of Reality_On the Multiverse
The Universe and Universes l Various Parallel Universes l Cosmic Order

2.
An endless string of doppelgangers_A multiverse stitched together
The Father of the Big Bang l General Relativity l The Universe and the Teapot l Gravitational Calculator l Primordial Atoms l Models and Data l Our Universe l Reality in the Universe l Infinite Space and the Stitched Quilt l Finite Possibilities l Cosmic Repetition l Only Physics! l Various Improbable Hypotheses

3.
Eternal Infinite Inflation Multiverse
Hot Creation Debris l The Amazingly Evenly Dispersed Early Photons l Faster Than Light! l Expanding Horizons l Quantum Fields l Quantum Fields and Inflation l Eternal Inflation l Swiss Cheese and the Universe l Changing Perspectives l Exploring the Inflationary Multiverse l The Universe in a Nutshell l The Space of the Bubble Universe

4.
Unification of the Laws of Nature: The Path to String Theory
A Brief History of Unification l The Comeback of Quantum Field Theory l String Theory l Strings, Points, and Quantum Gravity l The Dimensions of Space l Great Expectations l The Properties of Particles and String Theory l Experimental Verification of String Theory l String Theory, Singularities, and Black Holes l String Theory and Mathematics l The Current State and Evaluation of String Theory

5.
Flying through space in neighboring dimensions: The Brane Multiverse and the Periodic Multiverse
Beyond Approximation l Duality l Branes l Branes and Parallel Universes l Sticky Branes and Gravitational Tentacles l Time, Cycles, and the Multiverse l Past and Future of the Periodic Universe l Multiverse

6.
A New Look at Old Constants: The Landscape Multiverse
The Second Coming of the Cosmological Constant l The Density of the Universe l Distance and Brightness l What is the Distance Between What? l The Colors of Cosmology l The Expansion Acceleration of the Universe l The Cosmological Constant l Why Was the Cosmological Constant Thought to Be Zero? l The Cosmic Anthropometry l Life, Galaxies, and the Numbers of Nature l Flaws Turned into Strengths l The Final Steps l The String Landscape l The Quantum Tunnel l What Happens to the Rest of Physics? l Can This Really Be Called Science?

7.
Science and the Multiverse: On Inference, Explanation, and Prediction
The Spirit of Science l The Accessible Multiverse l Science and the Unreachable World 1 l Science and the Unreachable World 2 l Predictions of the Multiverse Theory 1 l Predictions of the Multiverse Theory 2 l Predictions of the Multiverse Theory 3 l Predictions of the Multiverse Theory 4 l Dividing by Infinity l Concerns of Opponents l Mystery and the Multiverse

8.
The Multiverse of Quantum Observation_The Quantum Multiverse
Quantum Reality | The Puzzle of Choice | Quantum Waves | Don't Jump to Conclusions! | Imperfect Linearity | Many Worlds | Two Stories | When Will Other Universes Appear? | Uncertainties in Advanced Theories | Likely Problems | Probability and Many Worlds | Prediction and Understanding

9.
Black Holes and Holograms_Holographic Multiverse
Information l Black Holes l The Second Law l The Second Law of Thermodynamics and Black Holes l Hawking Radiation l Entropy and Hidden Information l Entropy, Hidden Information, and Black Holes l Finding Hidden Information in Black Holes l Beyond Black Holes l Details l String Theory and Holography l Parallel Universes or Parallel Mathematics? l The Future of String Theory

10.
The Universe, Computers, and Mathematical Reality: The Simulation Multiverse and the Ultimate Multiverse
Creating the Universe l The Stuff of Thought l A Simulated Universe l Are You Living in a Simulation? l Beyond Simulation l Babel? Library l Rationalizing the Multiverse l Babel Simulation l The Roots of Reality

11.
The Limits of Exploration: The Multiverse and the Future
Is the Copernican pattern fundamental? l Can scientific theories based on the multiverse be tested? l Are the multiverse theories discussed so far testable? l How does the multiverse affect the scientific description of nature? l Is mathematics reliable?

Translator's Note
Huzhou
References
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“The history of the universe from 13.7 billion years ago flashes before our eyes like a flash of lightning.

Brian Greene's refreshingly unravels the wondrous secrets we hold about the universe.
“Multiverse is the one science book you should pick up this year!”_The New York Times

The latest sensational work from Brian Greene, a world-renowned theoretical physicist who pioneered a unique field of cosmology!
What if our universe isn't one, but many?
Does the multiverse really exist?

What if our universe isn't one, but many? What if another me, in another universe, lives a completely different life from this one? These are questions we've all likely pondered at least once.
For us who live in a harsh world where once we make a choice, there is no turning back, the multiverse is certainly a fascinating concept.


Parallel universes are no longer science fiction or fantasy.
Author Brian Greene emphasizes that “the physical multiverse theory is not a product of speculative philosophy, but rather an inevitable consequence of the expansion of existing theories.”
And this book, "Multiverse," redefines the meaning of human existence and the future at the forefront of modern, cutting-edge science, elucidates the "existence of the multiverse," and provides a grand insight into the revolutionary changes in the universe, which is endlessly expanding and being created even at this very moment.
Brian Greene, who rose to stardom in the world of physics with his previous works, The Elegant Universe and The Space of the Universe, becoming global bestsellers, has now published a new book in seven years. This book easily and enjoyably explains the cutting-edge reality of the universe and modern physics in the midst of a huge paradigm shift, including dimensional universes, chaotic universes, brain multiverses, and simulated universes.


1｜History of Cosmology
“Only when one world collapses can a new world unfold!”
Before delving into the full-fledged multiverse theory, Green briefly summarizes cosmology from ancient times to the present.
Cosmology is the study of the origin and development of the universe in which we live, and the existence and future of humans within the universe.
The study of cosmology to elucidate these is not limited to astronomy alone.
Cosmology is a discipline that is completed through the integrated operation of all academic fields, including cutting-edge mathematics, logic, and physics.
And the study of the existence of matter and life inevitably raises fundamental questions about matter and life, expanding beyond the natural sciences to include the academic fields of ethics and philosophy.
The development of scientific cosmology can be broadly divided into three periods.

The history of cosmology begins with the geocentric theory, which was accepted as the established theory for 2,000 years since it was proposed by Aristotle of ancient Greece.
Ancient cosmology, whose boundaries with philosophy and religion were vague, underwent major changes with Copernicus' heliocentric theory and was finally incorporated into the realm of modern science with Newton's theory of gravity.
Cosmology in the modern sense began with Einstein, and through his special and general theories of relativity, Einstein opened the door to modern cosmology by elucidating the geometric properties of space-time and the understanding of space-time in a static universe.
However, Einstein's theory, which was accepted as absolute knowledge, was later accepted by astronomer Edwin Hubble that the universe is not static but expands, and the Big Bang theory was born.

2｜What is a multiverse, and how does it come into being?
“Does another reality exist?”
As briefly discussed above, before the Big Bang theory, we tried to explain the universe by assuming a single, static universe.
However, with the birth of the Big Bang theory, by abandoning the paradigm of a single universe, a vast possibility (the possibility of a multiverse) opened up before us.
Greene, through this book, reveals the hidden reality of the universe, that is, the reality of other universes outside of ours, through not just theoretical hypotheses, but also physical insights and experimental evidence, such as studies of the sky (microwave cosmic background radiation) that contain traces of when the universe was born and expanded rapidly, and through evidence from string theory that unifies the theory of gravity and quantum mechanics, as well as mathematical logic.


At the moment our universe was born, temperatures soared to incredible heights, and a tremendous amount of energy was released in a single explosion, giving birth to the universe.
Immediately after the Big Bang, for a very short period of time, the original universe expanded at an incredibly fast rate.
Like a bubble.
During this brief moment of expansion, the foundations of the universe we live in were formed, and the bubble that expanded during that time formed the universe that now surrounds us.


What we see is only a very small part of the real universe.
If our universe is truly infinitely large, a strange logic holds.
In an infinitely large universe, the finite arrangement of atoms and molecules will inevitably repeat itself, until all possibilities are exhausted and the same possibilities will emerge.
This means that we can create beings similar or identical to us.
In other words, if the universe is infinitely vast and creates countless bubble-like universes, then the patterns that form our bodies and the matter that exists on Earth repeat countless times, leading us to conclude that our lives right now may be repeating themselves somewhere in the multiverse.

The Philosophical Implications of the Multiverse
“Man is insignificant and insignificant on a cosmic scale, but in another sense he is the creator of the world!”
In the world of classical mechanics, if the state of the universe at that time could be perfectly understood and analyzed, then all of the universe's past and future were predictable, or in other words, determined.
There is absolutely no room for human free will to intervene here.
However, with the advent of quantum mechanics, we can only know probabilities, and deterministic predictions are no longer possible.
In quantum mechanics, human free will intervenes in the process of moving from probability to result by introducing a variable called 'observation'.
In this way, when various possibilities are determined to a single value through observation in the process of interpreting the multiverse, the universe can be divided into several branches.
Free will determines which of these many universes we will go to.


It is at this point that the brilliance of Brian Greene's writing comes to the fore.
Greene has clearly organized and explained the nine multiverses (the quilted multiverse, the inflationary multiverse, the brane multiverse, the periodic multiverse, the landscape multiverse, the quantum multiverse, the holographic multiverse, the simulation multiverse, and the ultimate multiverse) that have branched off from this free will and are leading the history of modern cosmology in various ways according to the development of cutting-edge modern physics, and in this one book, he has drawn a complete topography of physics and cosmology from ancient times to the present.

This book also makes us reflect on ourselves by asking fundamental questions about humanity.
If we live in one of many universes, we might think that our place and importance in the universe is diminished.
But in reality, value on a cosmic scale has nothing to do with relative rarity.
It is clear that the conditions for the birth of life (such as the formation of galaxies, stars, and planets) to be created in the universe, for life to actually be born somewhere and evolve over a long period of time, and for life to eventually emerge with advanced intelligence, are very demanding.
Our very existence as humans is a crucial clue to the fundamental secrets of our universe.
And if there are multiple universes, it is conceivable that each of them cannot be separated into separate 'disconnected' regions.
For example, Universe A and Universe B do not exist separately in isolated areas, but are clearly ‘interacting’.
In this respect, 'human free will and choice' will play a decisive role in the future of modern physics, on a small scale, and of the universe we live in or other universes we do not know about, on a large scale.


《Multiverse》 simply and clearly introduces the process by which the multiverse hypothesis was inevitably introduced into physics theory and the knowledge necessary to understand it - classical mechanics, relativity, quantum mechanics, string theory, etc. and their achievements.
It covers everything from Newton's physics, which believed time was absolute, to Einstein's, which showed that time is relative, to quantum theory, which revealed that space is also like an 'entangled ring', to string theory, which asserts that other 'dimensions' are hidden within ordinary space-time. Therefore, it is not a specialized and difficult book on the 'multiverse', the greatest challenge of modern physics, but rather the best popular science book that clearly introduces the core and meaning of human cosmology.


And as previously discussed, Greene, following the elimination of human subjectivity from ancient scientific theories, which were indistinguishable from religion, philosophy, and ethics, revived human "free will" in modern scientific theories, thereby elucidating the complementary relationship between science and philosophy through mathematical logic and physical insight.
This proves, not with words, but with irrefutable evidence that natural science and humanities are destined to go together, rather than with philosophy being separate from science or ethics being separate from science.

By abandoning the paradigm of a single universe, vast possibilities open up before us.
Nothing has been established as a definitive new paradigm yet.
But which is truly the reality—the monoverse, the multiverse, or some other theory? No one knows the answer.
But to understand our limitations and find the vast truth, we must constantly pursue rational theories.
Multiverse will be a comprehensive guide to the evidence for other universes beyond our own, deepening our understanding of the universe through mathematical logic and physical insights, and bringing us one step closer to extending our thinking across the vast realm of reality and the entire universe.