From Paul Di Filippo's "THE SPECULATOR" column on The Barnes & Noble Review
The concept of the multiverse -- a plethora of individually infinite universes of every conceivable nature, coexisting yet separated from each other in some fashion -- holds a particular horror for those who fancy that their lives derive meaning and ethical stature only from a sense of self-determined uniqueness. Ontological nausea and revulsion swiftly set in when such a person begins to contemplate billions of his doppelgangers enacting perverse, bizarre, and morally repulsive scenarios imbued with just as much existential gravitas as the one his particular consciousness in this universe experiences and privileges. Such a vision embodies self-betrayals of the most intimate possible nature.
for those of us who relish the notion of a limitless plenum in which every
possible outcome of consciousness, every possible arrangement of matter, every
possible set of natural laws, is given concrete expression somewhere -- even
though these other universes lie forever beyond our reach -- the concept of the
multiverse offers a triumph of the imagination and spirit. No flight of fancy,
however wild, is denied existence. Every potential aspect of one's character,
suppressed in this universe, finds manifestation elsewhere. Bad fates in this
universe are avoided in an infinity of others. And the multiverse settles all
perplexing questions of "Why this?" with a simple "Because we
see only one thread of an infinite tapestry."
you cannot really avoid forming a reaction to the notion of a multiverse
either -- assuming you respect science -- since almost all contemporary physics
accepts and even demands the reality of parallel worlds. Love it or hate it,
the multiverse is here to stay.
It's not hard to guess -- in advance of reading Brian Greene's latest survey of the actual physics behind the multiverse, The Hidden Reality -- which side of the emotional fence he comes down on. Having gone to the effort of producing a hypnotically fascinating book-length explication of the concept, Greene is plainly invested deeply in the awesomeness of multiple realities. His enthusiasm and passion for parallel worlds infuses every iota of this ideationally dense yet essentially comprehensible opus.
informs us at the outset that he will explicate nine types of multiverses. (Yes,
we are about to encounter a multiverse of multiverses!) The first seven are
direct outgrowths of discoveries or theories in modern physics: cosmology, string
theory, etc. The final two are more purely conceptual or speculative exercises.
So, because the first set requires grounding in several branches of science,
Greene devotes plenty of space to topics that are foundational: how gravity
works, the Inflationary Big Bang, and so forth. Admirably, he skips the boring
and redundant primer level, which so many popular science books continue
timidly to include at this late date, but assumes that his readership of
interested twenty-first-century laypeople has a solid acquaintance already with
the science of the past hundred years. This tactic is much appreciated, and
never abused, as any sticky or abstruse points are still treated with
appropriate depth in Greene's trademark crystalline prose studded with handy
and often amusing metaphors. ("Imagine you work for the notorious film
producer Harvey W. Einstein, who has asked you to put out a casting call for
the lead in his new indie, Pulp Friction.")
impossible for this review to summarize every step of Greene's balletic
footwork, by which, like some multi-limbed Asian deity, he dances into being
each different theoretical framework that could support multiple universes. Suffice
it to say, switching analogies, that his arguments are constructed like
classical cathedrals, with intricate arches and buttresses that all uphold the
central spire. Sometimes you think he's lost in the details of some sculpted
gargoyle, only to realize how essential to the whole structure this particular
starts with the simplest of multiverses, the "Quilted" one. In this
case, a purely spatial infinity is all that is needed to produce an infinity of
timelines, separated merely by lightyears and not other dimensions. He
concludes with the "Ultimate" multiverse, a philosophical construct
owing much to the speculations of Robert Nozick. In between, we get bubble
universes and "branes" and five other mind-boggling ways in which the
cosmos we know can be viewed as merely one member of an endless family of
Seven, coming right at the midpoint of the book, is a very useful diversion
from propounding new theories, a breather in which Greene examines the
controversies surrounding the very notion of a multiverse, and whether these
speculations that cannot be tested, observed, or falsified truly adhere to the
spirit of science. Coming down staunchly on the side of unfettered yet rigorous
hypothesizing (and leaving open the possibility that our descendants will be
able someday to verify our flights of scientific fancy), Greene emerges prepped
to ascend even greater heights in the second half of the book.
tension between the two camps -- lovers and haters of the multiverse -- that I
described in my opening paragraphs is a constant motif throughout the book, as
Greene continually seeks to justify the rewards inherent in accepting "the
hidden reality" of the multiverse. His concluding sentences sum up his
stance bravely and concisely: "But it's only through fearless engagement
that we can learn our own limits. It's only through the rational pursuit of
theories, even those that whisk us into strange and unfamiliar domains, that we
stand a chance of revealing the expanse of reality."
* * *
namechecks several fictional treatments of multiversal concepts in his opening
chapter -- Star Trek's "The City on the Edge of Forever," Borges's
"The Garden of Forking Paths," Run Lola Run -- and indeed this
concept has received extensive treatment in science fiction and other types of
literature, rendering its outlines familiar to even the most casual reader and
viewer. The well-developed scientific treatment of parallel worlds in
literature goes back at least as far as H. G. Wells, and has received extensive
elaboration from writers as diverse as Edmond Hamilton and Fritz Leiber, Robert
Silverberg and Keith Laumer.
enough, one of the most seminal and impactful introductions of the concept
occurred in a comic book, the now-classic September 1961 issue of The Flash,
with its feature story "Flash of Two Worlds." Scripter Gardner Fox,
long-steeped in pulp writing, imported the notion of multiple timelines to the
home turf of Superman and Batman (Marvel Comics belatedly followed suit), and
an explosion of multiversal narratives ensued, to the point where parent
company DC Comics felt obliged to stage Crisis on Infinite Earths some twenty years later,
to pare down the proliferation of alternate worlds.
if one had to pick a single author who has done the most to portray the quirks
and potentials of a functioning multiverse, that figure would undeniably be Michael Moorcock. First employing the
concept almost five decades ago, Moorcock has since woven nearly all his
copious output -- tightly or loosely, as circumstances allow -- into one vast braided
multiverse of story. So identified is Moorcock with the multiverse, in fact,
that upon his ascent to SFWA Grandmaster, I was able to easily evoke a humorous
scenario involving the author and
his doppelgangers that any of his readers would instantly recognize.
latest, Elric: Swords and Roses, is the sixth and
concluding installment in his chronicle of the doomed, Byronic, albino
swordsman who functions as a kind of template or seed character for so many
other antiheroes in the Moorcock multiverse.
open the omnibus (which also contains a previously unpublished screenplay, a
novella, and several essays, as well as pages of artwork) with its core
component, a complete novel from 1991, The Revenge of the Rose. Whereas
many of Elric's early adventures dealt with the multiverse only implicitly,
this late-period outing foregrounds the nature of creation in Moorcock's fiction.
The multiverse nearly assumes the role of an actor in the adventure. For
beneath the expected inventive sword-and-sorcery decadence (Elric, a woman
warrior named Rose, and a poet named Wheldrake are all plucked from their separate
timestreams for exploits in a strange world foreign to them all, as Elric hunts
for the plot-coupon soul-in-a-box of his dead father), Elric must continually
confront the senses-disturbing and mind-shattering -- yet also uplifting -- nature of
Elric was caught up in a kind of intradimensional hurricane, in which a
thousand reverses ocurred within his brain at once and he became a thousand
other creatures for an instant, and where he lived through more than ten other
lives; a fate only minimally different from the one that was familiar to him;
and so vast did the multiverse become, so unthinkable, that he began to go mad
as he attempted to make sense of just a fraction of what laid siege to his
the upside is this vision, as recounted by a seer:
is our firm belief that we shall one day learn the plan of the entire
multiverse and travel at will from Sphere to Sphere, from realm to realm, from
world to world, travel through the great clouds of shifting, multicoloured
stars, the tumbling planets in all their millions, through galaxies that swarm
like gnats in a summer garden, and rivers of light -- glory beyond glory -- pathways
of moonbeams between the roaming stars.
thus, through Moorcock's exuberant prose, is Brian Greene's carefully controlled and channeled mysticism -- the unnamed
engine that powers his researches, yet which must be throttled in the name of
science and hidden away -- given ultimate lyrical expression.
Read an Excerpt
The Bounds of Reality
On Parallel Worlds
If, when I was growing up, my room had been adorned with only a single mirror, my childhood daydreams might have been very different. But it had two. And each morning when I opened the closet to get my clothes, the one built into its door aligned with the one on the wall, creating a seemingly endless series of reflections of anything situated between them. It was mesmerizing. I delighted in seeing image after image populating the parallel glass planes, extending back as far as the eye could discern. All the reflections seemed to move in unison—but that, I knew, was a mere limitation of human perception; at a young age I had learned of light’s finite speed. So in my mind’s eye, I would watch the light’s round-trip journeys. The bob of my head, the sweep of my arm silently echoed between the mirrors, each reflected image nudging the next. Sometimes I would imagine an irreverent me way down the line who refused to fall into place, disrupting the steady progression and creating a new reality that informed the ones that followed. During lulls at school, I would sometimes think about the light I had shed that morning, still endlessly bouncing between the mirrors, and I’d join one of my reflected selves, entering an imaginary parallel world constructed of light and driven by fantasy. It was a safe way to break the rules.
To be sure, reflected images don’t have minds of their own. But these youthful flights of fancy, with their imagined parallel realities, resonate with an increasingly prominent theme in modern science—the possibility of worlds lying beyond the one we know. This book is an exploration of such possibilities, a considered journey through the science of parallel universes.
Universe and Universes
There was a time when “universe” meant “all there is.” Everything. The whole shebang. The notion of more than one universe, more than one everything, would seemingly be a contradiction in terms. Yet a range of theoretical developments has gradually qualified the interpretation of “universe.” To a physicist, the word’s meaning now largely depends on context. Sometimes “universe” still connotes absolutely everything. Sometimes it refers only to those parts of everything that someone such as you or I could, in principle, have access to. Sometimes it’s applied to separate realms, ones that are partly or fully, temporarily or permanently, inaccessible to us; in this sense, the word relegates ours to membership in a large, perhaps infinitely large, collection.
With its hegemony diminished, “universe” has given way to other terms introduced to capture the wider canvas on which the totality of reality may be painted. Parallel worlds or parallel universes or multiple universes or alternate universes or the metaverse, megaverse, or multiverse—they’re all synonymous and they’re all among the words used to embrace not just our universe but a spectrum of others that may be out there.
You’ll notice that the terms are somewhat vague. What exactly constitutes a world or a universe? What criteria distinguish realms that are distinct parts of a single universe from those classified as universes of their own? Perhaps someday our understanding of multiple universes will mature sufficiently for us to have precise answers to these questions. For now, we’ll use the approach famously applied by Justice Potter Stewart in attempting to define pornography. While the U.S. Supreme Court wrestled mightily to delineate a standard, Stewart declared simply and forthrightly, “I know it when I see it.”
In the end, labeling one realm or another a parallel universe is merely a question of language. What matters, what’s at the heart of the subject, is whether there exist realms that challenge convention by suggesting that what we’ve long thought to be the universe is only one component of a far grander, perhaps far stranger, and mostly hidden reality.
During the last half century, science has provided ample ways in which this possibility might be realized.
Varieties of Parallel Universes
A striking fact (it’s in part what propelled me to write this book) is that many of the major developments in fundamental theoretical physics— relativistic physics, quantum physics, cosmological physics, unified physics, computational physics—have led us to consider one or another variety of parallel universe. Indeed, the chapters that follow trace a narrative arc through nine variations on the multiverse theme. Each envisions our universe as part of an unexpectedly larger whole, but the complexion of that whole and the nature of the member universes differ sharply among them. In some, the parallel universes are separated from us by enormous stretches of space or time; in others, they’re hovering millimeters away; in others still, the very notion of their location proves parochial, devoid of meaning. A similar range of possibility is manifest in the laws governing the parallel universes. In some, the laws are the same as in ours; in others, they appear different but have shared a heritage; in others still, the laws are of a form and structure unlike anything we’ve ever encountered. It’s at once humbling and stirring to imagine just how expansive reality may be.
Some of the earliest scientific forays into parallel worlds were initiated in the 1950s by researchers puzzling over aspects of quantum mechanics, a theory developed to explain phenomena taking place in the microscopic realm of atoms and subatomic particles. Quantum mechanics broke the mold of the previous framework, classical mechanics, by establishing that the predictions of science are necessarily probabilistic. We can predict the odds of attaining one outcome, we can predict the odds of another, but we generally can’t predict which will actually happen. This well-known departure from hundreds of years of scientific thought is surprising enough. But there’s a more confounding aspect of quantum theory that receives less attention. After decades of closely studying quantum mechanics, and after having accumulated a wealth of data confirming its probabilistic predictions, no one has been able to explain why only one of the many possible outcomes in any given situation actually happens. When we do experiments, when we examine the world, we all agree that we encounter a single definite reality. Yet, more than a century after the quantum revolution began, there is no consensus among the world’s physicists as to how this basic fact is compatible with the theory’s mathematical expression.
Over the years, this substantial gap in understanding has inspired many creative proposals, but the most startling was among the first. Maybe, that early suggestion went, the familiar notion that any given experiment has one and only one outcome is flawed. The mathematics underlying quantum mechanics—or at least, one perspective on the math— suggests that all possible outcomes happen, each inhabiting its own separate universe. If a quantum calculation predicts that a particle might be here, or it might be there, then in one universe it is here, and in another it is there. And in each such universe, there’s a copy of you witnessing one or the other outcome, thinking—incorrectly—that your reality is the only reality. When you realize that quantum mechanics underlies all physical processes, from the fusing of atoms in the sun to the neural firing that constitutes the stuff of thought, the far-reaching implications of the proposal become apparent. It says that there’s no such thing as a road untraveled. Yet each such road— each reality—is hidden from all others.
This tantalizing Many Worlds approach to quantum mechanics has attracted much interest in recent decades. But investigations have shown that it’s a subtle and thorny framework (as we will discuss in Chapter 8); so, even today, after more than half a century of vetting, the proposal remains controversial. Some quantum practitioners argue that it has already been proven correct, while others claim just as assuredly that the mathematical underpinnings don’t hold together.
What is beyond doubt is that this early version of parallel universes resonated with themes of separate lands or alternative histories that were being explored in literature, television, and film, creative forays that continue today. (My favorites since childhood include The Wizard of Oz, It’s a Wonderful Life, the Star Trek episode “The City on the Edge of Forever,” and, more recently, Sliding Doors and Run Lola Run). Collectively, these and many other works of popular culture have helped integrate the concept of parallel realities into the zeitgeist and are responsible for fueling much public fascination with the topic. But the mathematics of quantum mechanics is only one of numerous ways that a conception of parallel universes emerges from modern physics. In fact, it won’t be the first I’ll discuss.
Instead, in Chapter 2, I’ll begin with a different route to parallel universes, perhaps the simplest route of all. We’ll see that if space extends infinitely far—a proposition that is consistent with all observations and that is part of the cosmological model favored by many physicists and astronomers—then there must be realms out there (likely way out there) where copies of you and me and everything else are enjoying alternate versions of the reality we experience here. Chapter 3 will journey deeper into cosmology: the inflationary theory, an approach that posits an enormous burst of superfast spatial expansion during the universe’s earliest moments, generates its own version of parallel worlds. If inflation is correct, as the most refined astronomical observations suggest, the burst that created our region of space may not have been unique. Instead, right now, inflationary expansion in distant realms may be spawning universe upon universe and may continue to do so for all eternity. What’s more, each of these ballooning universes has its own infinite spatial expanse, and hence contains infinitely many of the parallel worlds explored in Chapter 2.
In Chapter 4, our trek turns to string theory. After a brief review of the basics, I’ll provide a status report on this approach to unifying all of nature’s laws. With that overview, in Chapters 5 and 6 we’ll explore recent developments in string theory that suggest three new kinds of parallel universes. One is string theory’s braneworld scenario, which posits that our universe is one of potentially numerous “slabs” floating in a higher-dimensional space, much like a slice of bread within a grander cosmic loaf. If we’re lucky, it’s an approach that may provide an observable signature at the Large Hadron Collider in Geneva, Switzerland, in the not too distant future. A second variety involves braneworlds that slam into one another, wiping away all they contain and initiating a new, fiery big-bang-like beginning in each. As if two giant hands were clapping, this could happen over and over—branes might collide, bounce apart, attract each other gravitationally, and then collide again, a cyclic process generating universes that are parallel not in space but in time. The third scenario is the string theory “landscape,” founded on the enormous number of possible shapes and sizes for the theory’s required extra spatial dimensions. We’ll see that, when joined with the Inflationary Multiverse, the string landscape suggests a vast collection of universes in which every possible form for the extra dimensions is realized.
In Chapter 6, we’ll focus on how these considerations illuminate one of the most surprising observational results of the last century: space appears to be filled with a uniform diffuse energy, which may well be a version of Einstein’s infamous cosmological constant. Indeed, this observation has inspired much of the recent research on parallel universes, and it’s responsible for one of the most heated debates in decades on the nature of acceptable scientific explanations. Chapter 7 extends this theme by asking, more generally, whether consideration of hidden universes beyond our own can be rightly understood as a branch of science. Can we test these ideas? If we invoke them to solve outstanding problems, have we made progress, or have we merely swept the problems under a conveniently inaccessible cosmic rug? I’ve sought to lay bare the essentials of the clashing perspectives, while ultimately emphasizing my own view that, under certain specific conditions, parallel universes fall unequivocally within the purview of science.
Quantum mechanics, with its Many Worlds version of parallel universes, is the subject of Chapter 8. I’ll briefly remind you of the essential features of quantum mechanics, then focus on the formidable problem just referred to: how to extract definite outcomes from a theory whose basic paradigm allows for mutually contradictory realities to coexist in an amorphous, but mathematically precise, probabilistic haze. I’ll carefully lead you through the reasoning that, in seeking an answer, proposes anchoring quantum reality in its own profusion of parallel worlds.
Chapter 9 takes us yet further into quantum reality, leading to what I consider the strangest version of all parallel universes proposals. It’s a proposal that emerged gradually over thirty years of theoretical studies spearheaded by luminaries including Stephen Hawking, Jacob Bekenstein, Gerardt Hooft, and Leonard Susskind on the quantum properties of black holes. The work culminated in the last decade, with a stunning result from string theory, and it suggests, remarkably, that all we experience is nothing but a holographic projection of processes taking place on some distant surface that surrounds us. You can pinch yourself, and what you feel will be real, but it mirrors a parallel process taking place in a different, distant reality.
Finally, in Chapter 10 the yet more fanciful possibility of artificial
universes takes center stage. The question of whether the laws of physics give us the capacity to create new universes will be our first order of
business. We’ll then turn to universes created not with hardware but
with software—universes that might be simulated on a superadvanced computer—and investigate whether we can be confident that we’re not now living in someone or something else’s simulation. This will lead to the most unrestrained parallel universe proposal, originating in the philosophical community: that every possible reality is realized somewhere in what’s surely the grandest of all multiverses. The discussion naturally unfolds into an inquiry about the role mathematics has in unraveling the mysteries of science and, ultimately, our ability, or lack thereof, to gain an ever-deeper understanding of the expanse of reality.
The Cosmic Order
The subject of parallel universes is highly speculative. No experiment or observation has established that any version of the idea is realized in nature. So my point in writing this book is not to convince you that we’re part of a multiverse. I’m not convinced—and, speaking generally, no one should be convinced—of anything not supported by hard data. That said, I find it both curious and compelling that numerous developments in physics, if followed sufficiently far, bump into some variation on the parallel universe theme. Of particular note, it’s not that physicists are standing ready, multiverse nets in their hands, seeking to snare any passing theory that might be slotted, however awkwardly, into a parallel- universe paradigm. Rather, all of the parallel-universe proposals that we will take seriously emerge unbidden from the mathematics of theories developed to explain conventional data and observations.
My intention, then, is to lay out clearly and concisely the intellectual steps and the chain of theoretical insights that have led physicists, from a range of perspectives, to consider the possibility that ours is one of many universes. I want you to get a sense of how modern scientific investigations— not untethered fantasies like the catoptric musings of my boyhood— naturally suggest this astounding possibility. I want to show you how certain otherwise confounding observations can become eminently understandable within one or another parallel-universe framework; at the same time, I’ll describe the critical unresolved questions that have, as yet, kept this explanatory approach from being fully realized. My aim is that when you leave this book, your sense of what might be— your perspective on how the boundaries of reality may one day be redrawn by scientific developments now under way— will be far more rich and vivid.
Some people recoil at the notion of parallel worlds; as they see it, if we are part of a multiverse, our place and importance in the cosmos are marginalized. My take is different. I don’t find merit in measuring significance by our relative abundance. Rather, what’s gratifying about being human, what’s exciting about being part of the scientific enterprise, is our ability to use analytical thought to bridge vast distances, journeying to outer and inner space and, if some of the ideas we’ll encounter in this book prove correct, perhaps even beyond our universe. For me, it is the depth of our understanding, acquired from our lonely vantage point in the inky black stillness of a cold and forbidding cosmos, that reverberates across the expanse of reality and marks our arrival.
From the Hardcover edition.