The Number of the Heavens: A History of the Multiverse and the Quest to Understand the Cosmos

by Tom Siegfried

"One of the most controversial, cutting-edge ideas in cosmology-the possibility that there exist multiple parallel universes-in fact has a long history. Tom Siegfried reminds us that the size and number of the heavens have been contested since ancient times. His story offers deep lessons about the nature of science and the quest for understanding"--

Genres: Science, Nonfiction, Physics, History Of Science

Unknown Binding

First published September 17, 2019

Reviews

[Mansoor · Rating 1 out of 5]

It's a shame that Harvard University Press published this piece of propaganda. I mean there is a section titled "MULTIVERSE DENIERS!" 🤣 (Famed Iranian theoretical physicist Cumrun Vafa is one of those "deniers" not mentioned in the book, btw.) In chap. 11 Siegfried somehow manages to acknowledge that the multiverse idea has nothing to do with many-worlds interpretation of quantum mechanics: "The atomists’ dreams of many universes have been fulfilled not by quantum mechanics, but by inflationary cosmology." I only have one question: why doesn't Siegfried mention the negative results from the LHC run-ups?

PS If you're a fan of hardcore SF, you might want to take a look a this book.

[Steven H · Rating 5 out of 5]

A FINE HISTORY OF THE CONCEPTS OF ‘MULTIVERSE,’ ‘MANY WORLDS,’ ETC.

Author and science writer Tom Siegfried wrote in the Preface to this 2019 book, “medieval philosophers revisited the possibility of a plurality of worlds. Scholars continued to debate that proposition over the centuries that followed… scientists revised their notion of what constitutes the ‘world,’ or the universe… In the late twentieth century, the debate reignited as new data and theories about the cosmos lead many experts to suspect that our universe is not alone. Today cosmological authorities argue once again whether there is one universe or many---a multiverse. This book tells the story of this eternal debate, from the time of the ancient Greeks to the present… I make no attempt, though, to survey the wide range of ongoing research today relevant to the multiverse issue. That would take another whole book.”

He observes, “Without a multiverse, it seemed hard to explain why cosmic acceleration was going on now… Dark energy of just the right ‘Goldilocks’ strength would be needed for acceleration to begin when it did. Why should dark energy be just the right strength? Inflation’s multiplicity of universes provided a convenient answer. Its multiple bubbles could possess different amounts of dark energy; one of them had to have the right amount… Multiple universes are not a bug in inflationary theory; they are a feature.” (Pg. 27-28) The next 120 pages are a historical recounting of such theories developed by Robert Grossteste, Aristotle, Copernicus, etc.

Eventually he comes to Hugh Everett III, and he recounts: “There is no boss ‘outside’ the universe to make a measurement about what’s going on inside and select only one of the possibilities. And so, Everett decided, the answer was obvious: ALL the possibilities were real. If quantum mechanics describes a superposition of different possibilities, one observer’s measurement does not eliminate all but one of them---the others still exist. ‘It is therefore improper to attribute any less validity or ‘reality’ to any element of a superposition than any other element,’ Everett wrote. ‘All elements of a superposition must be regarded as simultaneously existing.’” (Pg. 193) He continues, “It is this aspect of Everett’s theory that suggests a splitting of the universe into branches---in one branch the mouse gets the cheese, in another the tree snaps.” (Pg. 194) Later, he adds, “[Everett] did not use phrases like ‘parallel universes’ or ‘many worlds.’ He seemed rather to believe in one universe that just so happened to encompass multiple branches of reality that sprouted in various directions as physical systems interacted.” (Pg. 196)

He explains that Bryce DeWitt “articulated the consequences of adopting Everett’s view. If quantum math accurately describes the universe, then ‘this universe is constantly splitting into a stupendous number of branches… Every quantum transition… is splitting our local world on earth into myriads of copies of itself.’ … he did not use the phrase ‘many-worlds interpretation… But in 1973, DeWitt and [Neill] Graham edited a book with the title ‘The Many-World Interpretation of Quantum Mechanics,’ and that is how Everett’s idea became generally labeled…” (Pg. 197-198)

He records, “For [Andrei Linde], the question was not why a particular mathematical structure describes nature’s particles and forces, but rather why we live in a place where math works so well. Inflation provides the answer, he said… Inflation provides bubbles with a variety of particles and forces; in some bubbles, mathematics can efficiently describe how those forces and particles interact to allow stable, complex structures to form. In realms where such stability is impossible, math would not be so useful.” (Pg. 218)

He states, “Depending on how the superstring approach was formulated, the math called for at least 10 dimensions, one of time, nine of space. At first some physicists suspected that those dimensions did not really need to exist---they merely served a mathematical purpose… It soon became clear to others that tiny strings and their extra dimensions did need to exist for the theory to represent reality. But everyone presumed that those extra dimensions were all very small… Space’s extra dimensions must have curled up, or compactified, into space that to our eyes and instruments disguised itself as merely three-dimensional.” (Pg. 239)

He acknowledges, “we can’t see the other ‘worlds’ prescribed by the Everett interpretation of quantum mechanics. But we can infer that they exist just as we infer that evolution occurred to produce the various life forms that we do observe. Evolution could have proceeded in many ways; different possible histories represent different branching trees among the possibilities. In the same way, we observe one of many different branches of possible quantum histories for the universe (or multiverse) we live in…. the multiverse (or multiverses) explains many of the regularities we see today in nature as a whole.” (Pg. 262)

He recounts that cosmologist George F.R. Ellis “repeats the objection that the multiverse idea that the multiverse is not testable because the other universes are beyond the cosmic horizon and cannot be observed… Ellis dismisses the multiverse as hypothetical, unsubstantiated, and a departure from rigorous scientific standards… Ellis makes a strong case that the multiverse if note scientifically established as a true and correct description of reality. The problem is that nobody says it is.” (Pg. 264-265)

He adds, “As for the lack of testable predictions made by multiverse theories, [Sean] Carroll has often pointed out that the multiverse is not itself a ‘theory’ that is supposed to make predictions—it is itself a prediction made by other theories… Carroll has reiterated the important point that an unobservable multiverse can explain observable things.” (Pg. 266-267)

He summarizes, “As things stand, the modern multiverse is certainly not regarded as settled science. Inflationary cosmology, while very successful in many respects, has not been verified beyond all plausible doubt. Superstring theory remains unverified, and the string landscape… might or might not survive further theoretical developments. So the multiverse today is … a possibility embraced by some but rejected by others.” (Pg. 268-269) He adds, “So when the multiverse deniers are saying it’s not science, they are presupposing a definition of science that rules out multiverses to begin with. And that’s not scientific.” (Pg. 279)

He concludes, “it is true that nobody really knows whether the multiverse picture of reality is correct. Inflationary cosmology and string theory (or M theory) may both predict a multiverse, but neither of those theories is yet established to be correct. They might turn out to be wrong… So maybe there are no other universes, no other quantum worlds, or no other extra dimensions for multiple branes to occupy. But maybe there are. And maybe we’ll never know…” (Pg. 280)

This book will be of great interest to those studying contemporary cosmological theories.

[Chris Jaffe · Rating 4 out of 5]

This is an engaging and (usually) easy to read history of how our understand of the nature of the universe has changed over the years. There's a theme through all of humanity's debates on the nature of the universe: it keeps getting bigger. Just when we think we've got one layer understood, turns out there's another layer beyond that even.

At first, the word "Universe" was essentially interchangeable with the world. Oh sure, there were the stars and moon and sun around the world - but the world was the center of all things, and those things were just lights circling the world we inhabit. So that's everything. The Bible said so. Aristotle said so. So it was.

In 1277, a Catholic Cardinal in France decreed that scholars couldn't rely on Aristotle as a definitive source. Normally religious edicts on world set science back, but this was the exception to the world. This helped spur on creative thought. Aristotle said that this was the only world. But, if we can't rely on him as our final word, maybe there are other worlds. This line of thought advanced even before Copernicus came along.

But Copernicus did come along and that was a massive change in how we viewed the universe. If the sun is just another star, and we're a planet orbiting it (instead of vice versa) and the other planets we see also orbit the sun - that creates a whole new view of the universe. We're just one planet among many circling one star among thousands of stars. Oh, and early telescopes show planets orbits Jupiter, too. Suddenly, it's impossible to confuse the world with the universe.

Some guys noticed that big Milky Way thing you can see in the night sky. Maybe that's a collection of stars. Maybe we're one of the stars on the edge of it. And so that became what was meant by the universe. We're one planet around one star among the multitude of stars in the universe called the Milky Way.

But it expanded again. We get telescopes that are better and notice some smudgy things on them. What are those? Well, it turns out many of them are just gas clouds, but some are other galaxies. The Milky Way isn't the entire universe. It's one galaxy among many. Andromeda is another nearby one. And plenty more exist. (Oddly enough, misreading some of those gas clouds helped popularize the notion of other galaxies - but the big picture was advanced even when the one detail was temporarily understood incorrectly).

So the Milky Way was one galaxy of many others in the universe. And we notice that galaxies, instead of being a stable state, are moving. They are typically moving away from each other. So we get the notion of the Big Bang. It happened and we've all been blowing out ever since. So that's the universe: the big thing created at the Big Bang.

People start looking at the post-Big Bang: Will it always keep expanding or not? There are scientific reasons to expect either continual expansion (caused by the Big Bang itself) or eventual contraction (caused by the sheer weight of the matter released in the Bang). But in the 1990s scientists made a discovery that upended a lot of thinking. Not only was the universe still expanding, but expansion was accelarating. The heck? That can't be explained by the Big Bang itself. That can't be explained at all. Yet it's going on. How is that possible?

Well, there's this theory kicked around from earlier call the multiverse. This universe is just one of many universes created at the Bang. All the Dark Energy and/or Dark Matter form the other Multiverses have created force which is causing acceleration. (Yeah, I'm a bit iffy in my understanding here, but oh well). There were other reasons to think the multiverse is real. Scientists have come around to a belief in inflation that occurred shortly after the Bang. This could cause little bubbles to emerge - and those bubbles could become universes, such as this one. Also, scientists have long pondered how miraculous it is that this universe is even capable of forming matter and stars in the first place. For matter to form galaxies and stars and planets as it does, it relies on some very delicate ratios and balancing act of the forces unleashed by the Big Bang. It the balancing was only slightly slightly slightly different, it would be impossible for matter to form in clusters the way it did. Really, the odds of this ratio being achieved are so incredibly slight, how could it happen? Well, it happened. If it was just one universe, it would be staggeringly unlikely. BUT it there were a countless number of universes, then hey - it makes sense it would happen to some universe. It actually mirrors the old debate about earth: if the distance to the sun or the elements in the atmosphere were only a little off, we'd never have life here. But it's all just perfect for it. If it's the only planet, then it's impossibly unlikely. But it's one of gazillions of planets, then it's likely.

The multiverse isn't proven or settled. Some still oppose it. But Siegfried notes that the arguments against it are making essentially the same arguments made by those who opposed believing in other galaxies or in other worlds. Existence keeps getting bigger whenever we look closer at it.

Some parts I didn't quite understand, especially later on when Siegfeid goes into depth on the nature of the multiverse. But I got a lot out of it anyway.

[Autumn Pisarsky · Rating 4 out of 5]

I really enjoyed reading this book, but it didn’t change my stance on the multiverse. I still think it’s unscientific and I still wonder why scientists pursue it.

My main disagreement is that the author assumes that science is the only way to find truth about the world. Philosophy and theology are fields where the same is also pursued in a different manner. Science has very specific presuppositions that outline what it can make claims on, and that the universe can be understood through the physical evidence we perceive is one of those presuppositions. Therefore, at the end when the author points out this is an unscientific claim, he is begging the question. Presuppositions are accepted without proof by definition. Naturally they are unscientific; they are the basis on which we outline what is science and what isn’t. It’s philosophy.

The argument could be resolved by admitting the multiverse is in the realm of philosophy until we find a way to test it. In the modern era, philosophy doesn’t hold the same prestige as science; however, I think taking this direction of argument would be more fruitful.

Overall, though, I really enjoyed reading about the history of the multiverse throughout the years and what notable scientists and philosophers have thought about the idea. The writing was witty and I laughed at several points. The author was fair in how he treated ideas from different belief systems than his. The language was accessible to the average reader and the accounts of current scientific understanding were fascinating. For those interested in further reading, the sources from which the author drew are listed, and they are myriad. I would and have recommended this book to others, and appreciate the author’s diligence.

[Cam Culbertson · Rating 3 out of 5]

I like books about cosmology written for the general reader. But overall, I found this to be a difficult read. The first half or so surveys a brief history of cosmology from Aristotle to the present day. I found all of that interesting. The theme is that the cosmos keeps expanding, literally and figuratively.

The latter half of the book examines various conceptions of the multiverse. As a person without training in physics and mathematics, I find these ideas dense and very difficult to envision. To me, they sound speculative at best, although I suppose some type of multiverse could be real.  If the point of this book was to convey these concepts to lay readers in a digestible and comprehensible manner, I think this book only does an average job.

The thesis is essentially that if we look at how our understanding of cosmology has expanded since ancient times, it's foolish to dismiss the multiverse out of hand (even though a multiverse is currently not observable). I suppose that's a reasonable argument.

These ideas are challenging and pique my curiosity. But if I'm honest, a lot of this sounds like it may be fancy and complicated nonsense. I'm not a mathematician or a physicist and I will keep an open mind. As this book teaches, the history of science shows us that we never know what we will discover in the future to reshape our understanding of reality.

[Kelly · Rating 3 out of 5]

Very difficult to rate this book. The attempt to make a connection between the modern-day concept of the multiverse and various historical ideas about other worlds fails. Additionally, way too much of the book is devoted to this attempt. The book's strength is its summarizing of the modern-day ideas around the multiverse (that part of the book deserves 5 stars). Between these two parts of the book, I was thinking of rating the book a 4, but the author's discussion of what is science is horrendous. He seems to have little in depth understanding of the epistemology of science and confuses what science is and what people have tried to prove true using science. That part of the book rated a 1 (or less). All in all, the first half of the book not worth reading. However, the summarization of modern-day multiverse theories did convert me from a disinterested multiverse sceptic to a curious multiverse sceptic and is well worth the read.

[Sally · Rating 3 out of 5]

An historical sketch of the controversy of many worlds/universes vs one world/universe, going from the ancient Greeks up to today with string theory, brane, multiverse, etc. Almost half the book deals with contemporary theories; the middle of the book is the historical survey. There is good information here, as one watches the world expand from the central earth with revolving heavenly spheres (Aristotle got it wrong again), to solar system with revolving spheres, to many suns, to galaxy, to island universes, and now the controversies about multiverses. A fascinating subject, but I felt the presentation was somehow lacking. 3-1/2 stars.

[Ed Kohinke sr. · Rating 5 out of 5]

I avidly read anything I can find on cosmology, and I especially liked this book because the author covered its history from ancient times to the present and included some interesting (and sometimes humorous) stories about many of the major players along the way. When it comes to strings, branes, and other such things I am still as clueless as ever about the multiverse concept, but that's my problem and not the author's! The book is yet another huge step in the direction of explaining the universe in factual terms, without totally dissing the creation mythologies of different religions.

[Zosia · Rating 3 out of 5]

(3.5) “I think it’s one of the tragedies that face the human species that there will always be a mystery about the universe.”

I so wanted to love this book because it’s a subject dear to my heart, but the first half was such a slog and the last half was only marginally better. You can’t say the author didn’t give a meticulously researched history of the multiverse, complete with several primary (modern) sources, but so much of this read like a Wikipedia page. The concepts and info were there! The writing was not.

[Redpoet · Rating 3 out of 5]

Some interesting history, but...

[Mattia Brambilla Pisoni · Rating 3 out of 5]

Great topic and well explained informative passages, but way too many useless quotations anecdotes. They are confusing and boring in a such complex topic if the aim is to be informative.

[Sean Staples · Rating 5 out of 5]

A lot of interesting concepts of the universe.

[Swathi Muthu · Rating 3 out of 5]

I really wanted to like this book. I thought it would tell an engaging story of all the ideas about the multiverse from history. Unfortunately, it was a Male-Eurocentric narrative that was verbose and uninteresting. The ideas weren’t new, but the author tries to represent them in a poetic language to keep the anudience engaged. Just not my cup of tea.