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What Lies Beneath
by Dan Falk
If science has taught us anything in the last 500 years, it is that there is much more to the universe than we can immediately sense. Our eyes, after all, tell us that the world is flat, that the sun revolves around the Earth, and that the stars are little specks of light sprinkled on an enormous, upside-down black bowl.
Galileo, condemned by the church for supporting the heliocentric view of Nicolaus Copernicus, is said to have muttered to his inquisitors under his breath, Eppur si muove (“and yet it moves”); he understood that our planet is a ball hurtling through space, a notion the average medieval mind would have found absurd. Judging the scale of the cosmos proved as difficult as judging its motions: The biggest surprise in Copernicus’ model of the heavens was not that the Earth revolves around the sun, but that the stars were more distant than anyone could have imagined.
Today, we measure those distances in light-years— remoteness that we can at least describe, if not readily grasp. The work of Edwin Hubble in the early twentieth century taught us that our Milky Way was just one of many galaxies, each containing billions of stars, scattered throughout a universe ma
ny millions of light-years across. The inner world, too, is not as it once seemed. Scientists found that the atom is buzzing with electrical and nuclear activity, at a scale far smaller than what our microscopes can show. There are at least two important lessons to draw from these insights: First, common sense is often wrong, simply because of our limited ability to perceive the world; second, the universe is vastly larger and stranger than it appears. As we’ve come to expect explanations for the universe to defy our senses, our fascination with such possible explanations has grown.
In recent years, string theory, popularized in books like celebrity physicist Brian Greene’s The Elegant Universe, has thoroughly captivated the collective imagination. The theory holds that the
universe is composed of tiny, vibrating strings, each a billion billion times smaller than an atomic nucleus, and is seen by some as the most promising attempt to unify gravity with the other forces of nature. Its details are staggeringly complex; for it to be consistent—that is, in order for the math to work out—a framework involving extra dimensions, possibly as many as ten or eleven, is required. Yet the notion of all these hidden dimensions has only enhanced the theory’s appeal.
Warped Passages, the first book by Harvard
University theoretical physicist Lisa Randall, is
one of the most recent to dive into the extra世界
纠结排行榜 dimensions, which, she explains, are probably all
around us, hidden from view, “curled up” on
scales far too small to probe with even the most
powerful microscope. As an analogy, Randall
suggests thinking of a garden hose: From far
away, it looks like a onedimensional line; it is only when we see it up close that a second dimension, the circumference of the hose, reveals itself. (Randall acknowledges she is not the first to use this particular analogy; many string theorists, including Greene, are fond of it.) The difference between strings and the garden hose is merely one of scale: String theory’s hidden dimensions are likely folded away on the order of 10–33 centimeters.
While the original version of string theory was weird enough, physicists in the 1990s developed a refined version known as M-theory. In this new scheme, one-dimensional strings give way to multidimensional “membranes,” or “branes” for short. As theorists, including Randall, investigated the properties of these branes, they found that not all of the extra dimensions needed to be curled up. Some of them, Randall and colleague Raman Sundrum discovered, could actually be infinite in size but escape detection because of the way the proposed branes would restrict the various forces of nature. That was big news for cosmologists, who had been conceptualizing a threedimensional universe (four, if you count time) that emerged from a big bang 13.7 billion years ago. Before long, there were “brane worlds,” new models of the universe inspired by M-theory that offered a startling new description of the cosmos. In some scenarios, the entire visible universe is merely a “3-brane”—a threedimensional membrane— embedded in a larger structure called the “bulk,” which has at least four space dimensions and one more for time.
In her book, Randall lays out these scenarios and grounds them in other developments in modern physics: the so-called “standard
model” of particle physics, the problem of gravity (it feels strong to us, but is actually by far the weakest force), the search for the Higgs boson (a particle thought to endow all other particles with m
ass), and speculations on the ultimate nature of space and time.
Lawrence Krauss, meanwhile, takes a longer-
range and broader approach to string theory,
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brane worlds, and hidden dimensions in his new
book, Hiding in the Mirror. Krauss, a physicist at
Case Western Reserve University and the author
全国人民代表大会设立民族委员会of six previous books on physics and science
fiction, covers much of the same ground as
Randall. While examining the science behind
these cutting-edge concepts, though, he also explores our cultural fascination with them. His account closely follows the rise of science from the time of Plato to the present, digressing in places into the realms of pop culture and art. Only in light of the last two millennia of Western thought, he suggests, can the intrigue of extra dimensions be understood.
“The luxuries of art and literature,” Krauss writes, can “create imaginary worlds that cause us to reconsider our own place within the world.” And while art is a quite different pursuit from science, which “unveils different sorts of hidden worlds … ones we hope might actually exist and, most importantly, can be measured,” the end result, he says, is the same: “We gain new insights into our own standing in the universe.”
Krauss eventually does lead us to the modern case for unseen dimensions and some of the cosmic scenarios inspired by string theory and M-theory. He explains the “ekpyrotic” and “cyclic” models of the universe, brane world scenarios in which what we call the big bang is reinterpreted as a collision between parallel branes. While string theory has not yet been tested by direct experiment, these examples illustrate how far its influence has already reached, with cosmologists taking its predictions 窄
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very seriously. Yet Krauss reminds us that the jury is still out on these latest proposals, and remains noncommittal about his own faith in the theory. His enthusiasm for it, he admits, has “run hot and cold” over the course of writing the book. In terms of its future promise, he writes: “There have been moments when the remarkable depth of the mathematical insights being explored in the course of recent years has left me awed, and there have been times when the sheer hubris of the claims, and the lack of associated results has left me shaking my head in disbelief.” Still, there is no doubt he considers the effort—the relentless theorizing, the
almost cabalistic mathematics— worth it. As far-off as it may yet be, he believes the ultimate theory will likely contain “at least a germ of present string theory ideas.”
barkhausenWith all the attention currently lavished on string theory and M-theory, it may surprise some people that there are arguments for still different frameworks by which to understand the cosmos. In his new book, Decoding the Universe, Charles Seife, a former writer for Science magazine and professor of journalism at New York University, argues that the fundamental framework for understanding the cosmos isn’t strings or membranes, but rather information—the stuff that flows through our computer chips and gets encoded in our genes.
This idea, of course, is not new. In the 1940s, at the same time the first electronic computers were being developed, mathematicians devised a rigorous way of quantifying information, giving birth to a new branch of science known as information theory. Closely linked to probability theory, information theory lays out the rules for encoding, manipulating, and transmitting information. When the encoding is done using a base-2 counting system—the kind used by electronic computers— the smallest unit of information is known as a “bit,” standing for “binary digit.” A message encoded by some other system — English letters, for example, or the notes of a musical score—could be reduced to a string of these bits (which is how books and songs are stored on computers and compact discs).
At first, it may seem that information theory has little to say about the nature of the cosmos. Yet Seife contends that it provides a framework that embraces many of the key ideas of modern physics, allowing us to interpret them at a deeper level. The scope that Seife presents is broader than that of either Randall or Krauss. In addition to thermodynamics, relativity, and quantum theory, information theory, he claims, can illuminate the big-bang theory of cosmology, and even genetics.
“Information,” he writes in the book’s introduction, “appears, quite literally, to shape our universe. … Information seems to be at the heart of the deepest paradoxes in science—the mysteries of relativity
and quantum mechanics, the origin and fate of life in the universe, the nature of the ultimate destructive power of the black hole, and the hidden order in a seemingly random cosmos.”
It is a bold claim. Sometimes, as in a section on thermodynamics, Seife’s argument seems persuasive enough; at other times, his case seems weaker. It is perhaps least convincing when it takes on relativity
and quantum theory. In arguing that relativity is a theory of information, he notes that the speed of light is the ultimate speed limit in the universe, which means there’s a limit to how fast information can get from place to place. Indeed, even when individual bits of matter or energy move faster than the speed of light— which can happen, Seife explains, referring to recently published experimental results—relativity is still not violated because information, or the flow of “bits,” can never be transmitted faster than light speed. The argument is an interesting one, but does not convincingly support the assertion that relativity is, at its core, a theory of information.
Even when Decoding the Universe falls short in its
claims, it is often fascinating. Applying
information theory to genetics, Seife tells us how
information, as carried through our genes, records
our history. In his discussion of the way DNA
molecules encode the information carried in our
genes, he writes that the code “can be reduced to a
string of bits, of 0s and 1s—two bits for each
chemical. As important as it is for life, from an information theorist’s point of view DNA is no different from any other medium that can store information.” That may be true, but one might wonder whether Seife is implying that life is simply a particular encoding of symbols. A few pages later, he writes: “Even though we are able to pass information from generation to generation and use our brains to cr
eate things as sublime as The Odyssey and as fascinating as quantum field theory, as far as scientists can tell, we are pretty much information- processing machines.”
Perhaps Seife is confusing the symbols themselves—the 0s and 1s, the molecules of DNA—with the content or meaning of those symbols. As philosophy students like to ask: Is Ludwig van Beethoven’s Fifth Symphony“just” a series of notes? Is William Shakespeare’s King Lear “just” a sequence of letters? The message may be encoded by a set of symbols, but it cannot be said that the message is the set of symbols. It needs to be read by someone or something in order to have meaning. (This dilemma also lies at the heart of the “machine consciousness” debate: Is a simulation of a conscious being the same as a conscious being? There is no consensus as yet, but, as philosophers remind us, a computer can simulate a hurricane with a sequence of 0s and 1s—without leaving damage in its wake.)
Ultimately, information theory may not prove to be the most useful construct for understanding the universe. String theory may prove no better. But the good news is that old scientific theories don’t collapse
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