confident that the whole package can be fi- news nanced through private sources. Under his 27- year leadership, Energy Management, a part- SCAN ner in Cape Wind, has built a number of nat- ural gas–fired plants in New England. Says Gordon: “We’re creating a national model for America’s energy and environmental future.” The U.S. Department of Energy is “watch- PASSING THE ing the Cape project very closely,” remarks CARBON BUCK Brian Parsons, a scientist with the DOE’s Na- tional Renewable Energy Laboratory. But the The Kyoto Protocol, an international agreement to curb size of the undertaking has raised some eye- emissions of global warming brows. “I’d be a little skeptical about starting gases, allows countries to trade OFFSHORE WIND FARMS, such as these in the North with something that big,” warns wind-farm emissions through a commodity Sea off the coast of Blyth in the U.K., are less likely to engineering expert Tim Cockerill, a research called a CO2 equivalent, which draw complaints of noise and unsightliness. fellow at the University of Sunderland in Eng- equals the amount of industrial greenhouse gases that have the land. Others in Europe, however, are think- heat-trapping ability of one metric acquisition is unnecessary. And, perhaps most ing along the same lines as Cape Wind. Re- ton of carbon dioxide. The supply of important, the huge turbines are out of sight searchers at the Dutch Offshore Wind Energy CO2 equivalents is severely limited. and earshot of most people. Initially fishermen Converter project are aiming for a single six- worried about their catch volume decreasing, megawatt offshore turbine by 2008. Contin- According to a trading group formed by the financial-services but several European studies suggest that the ued interest may prove within the decade firm Cantor Fitzgerald, the price heavily anchored turbines act like shipwrecks whether this alternative to fossil fuels is more of one CO2 equivalent ranges from and in fact improve fish numbers. than just a passing gust. $1 to $2 a year, although in the On the flip side, investment costs are future it may reach $5 to $9. mammoth. Cape Wind, having already in- Wendy Williams, based in Mashpee, Mass., Cape Wind claims that the 420-megawatt wind farm will vested several million dollars in planning stud- is studying technologies that reduce carbon displace a plant that would have ies, expects to spend a total of $600 million. emissions through a grant from the Fund for annually spewed 1.37 million

AMEC BORDER WIND James S. Gordon, president of Cape Wind, is Investigative Journalism. metric tons of carbon dioxide.

COSMOLOGY Been There, Done That THE BIG BANG MAY NOT HAVE BEEN A SINGULAR EVENT BY GEORGE MUSSER

ingularities are the toxic waste of cos- cially with the maturing of string theory, mology. Theories, let alone children, are physicists’ best candidate for a theory of S well advised not to touch anything with everything. Last fall cosmologists Paul Stein- an infinite density or temperature: the zero hardt of Princeton University and Neil Turok time of the big bang, say, or the very center of the University of Cambridge, building on of a black hole. At such places, physics dis- earlier work with Steinhardt’s graduate stu- solves into metaphysics. These mathematical dent Justin Khoury and string theorists Burt THE GREAT points admit of no explanation; they just are. A. Ovrut of the University of Pennsylvania To dispose of them, cosmologists usually have and Nathan Seiberg of the Institute for Ad- CYCLE OF BEING opted for burial. For instance, cosmic infla- vanced Study in Princeton, proposed that the The idea of a cycling universe tion—the favored mechanism for how our big bang is not a one-of-a-kind event but part seems to cycle around every now universe expanded from the big bang—does of a recurring cycle. “What we’re motivated and then. Its last appearance was not eliminate the primeval singularity but sim- by string theory to believe is that the big bang motivated by the possibility that the universe has enough matter to ply isolates it from today’s universe. is not what we’ve always thought—a begin- reverse its expansion and collapse Lately, though, a more thorough decon- ning of space and time, where temperature in a big crunch. Observations tamination is becoming a viable option, espe- and energy diverge,” Steinhardt says. “Rather have since ruled that out.

www.sciam.com SCIENTIFIC AMERICAN 25 Copyright 2002 Scientific American, Inc. news it is a transition between the current expand- And unlike inflation, the cyclic model natu- ing phase and a preexisting contracting phase.” rally incorporates the dark energy that is now SCAN Detoxifying singularities has long been causing cosmic expansion to accelerate: it is one of string theory’s major goals. According none other than the spring energy. to the theory, elementary particles ultimately Like a bicycle pump, the back-and-forth consist of wriggling strings, which have multi- motion of the fourth dimension puffs up the dimensional counterparts known as branes. volume of our three dimensions. The pump al- The intrinsic size of strings and branes pre- lows a little backflow, so just before each col- vents them from collapsing into points of in- lision, the branes contract slightly. But the finite density. The theory has already had density never becomes infinite. “The only thing some success in explaining black holes as a that is singular is that one dimension shrinks novel type of particle, and over the past to zero for one moment,” Turok says. “This decade it has inspired several alternatives to is the mildest of all possible singularities.” the standard picture of inflation. Unfortunately, a mild singularity is still a A CYCLE BUILT Like some of those alternatives, the cyclic singularity. String theory is too provisional to FOR TWO BRANES model is based on the idea that our universe is detoxify it fully, so researchers can’t be sure a three-dimensional brane that bounds a four- that some unsuspected effect won’t undo each Earlier models of the cycling dimensional space. Another brane—a parallel cycle’s careful preparation for the next. “How universe had a fatal flaw: the big universe—resides a subsubatomic distance do small perturbations come through the big crunch is not a perfect mirror image of the big bang. As space contracts, away. That universe is closer to you than your crunch and go out of it?” asks cosmologist photons gain energy at the expense own skin, yet you can never see or touch it. Andrei Linde of Stanford University, a lead- of the gravitational field, so the These two branes act as if connected by a ing critic of the model. “It is like throwing a universe ends up hotter than when spring, which pulls the branes together when chair into a black hole and expecting it to re- it started. No true cycle could they are far apart and pushes them apart materialize later.” And that is not the only develop; the model requires an ultimate beginning as surely as the when they are close. Thus, they oscillate to problem; the precise behavior of the spring- one-time big bang does. and fro. Periodically the branes hit and re- like force, for instance, seems rather ad hoc. bound like cymbals. To those of us stuck in- New observations of the cosmic micro- The new cyclic model solves that side one of the branes, the collision looks ex- wave background radiation should be able to problem. The accelerating actly like a big bang. The hot primordial soup confirm or dispel these misgivings. Whatever expansion wrought by dark energy dilutes the photons, so each bang was the energy dumped into the branes when becomes of the model, it has encouraged cos- begins afresh. (This acceleration they hit. The density fluctuations that seeded mologists to question conventional wisdom. fulfills the same role as inflation in galaxies began as wrinkles in the branes. Gabriele Veneziano of CERN, a pioneer of the standard big bang theory but Many a cosmological model has found- both string theory and its application to cos- occurs at a different point in cosmic ered on the question of these density fluctua- mology, says, “Thanks partly to the work of history.) The universe can be infinitely old, thereby eliminating tions. Observations indicate that the fluctu- Turok, Steinhardt and colleagues, our com- the puzzle of what came “before.” ations had the same amplitude no matter munity is much more ready to accept that the what their size. The cyclic model predicts ex- big bang was the outcome of something actly that—the only model besides inflation rather than the cause of everything.” CYCLIC COSMOLOGY posits that to do so. “Without any notion of inflation our universe and a twin—shown here as planes, but actually three- whatsoever, we are able to account for that A longer discussion appears at dimensional—periodically bounce near-scale-invariant spectrum,” Ovrut says. www.sciam.com/explorations/ off each other. “That really was a remarkable discovery.” 2002/021102cyclic/

1. The universes stop moving apart and 2. Even as they do so, each 3. They collide. A new big 4. The collision refills each

start to approach each other. universe continues to expand. bang commences. universe with matter. SAMUEL VELASCO

26 SCIENTIFIC AMERICAN MARCH 2002 Copyright 2002 Scientific American, Inc.