There was a time when "universe" meant all there is. Read more...
- Publisher: Books on Tape
- Date: Jan 2011
From the book
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...
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--Timothy Ferris, The New York Times Book Review" - Few living writers write so lucidly about such complicated stuff. In
"Mr. Greene has a gift for elucidating big ideas . . . Exciting and rewarding . . . [The Hidden Reality] captures and engages the imagination." - Janet Maslin, The New York Times
"It's impossible 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. . . 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 feature is." - Paul di Filippo, Barnes and Noble Review
"[Greene] leads the general reader on an excursion to the farthest and most mind-bending reaches of speculative physics . . . An exhilarating--if sometimes vertigo-inducing--journey." - Alden Mudge, Bookpage
"An in-depth yet marvelously accessible look inside the perplexing world of modern theoretical physics and cosmology . . . Greene presents a lucid, intriguing, and triumphantly understandable state-of-the-art look at the universe." - Publishers Weekly (Starred review)