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Scientific American Time
Introduction That simple question is probably asked more often today than ever. In our clock-studded society, the answer is never more than a glance away, and so we can blissfully partition our days into ever smaller increments for ever more tightly scheduled tasks, confident that we will always know it is 7:03 p.m.

Modern scientific revelations about time, however, make the question endlessly frustrating. If we seek a precise knowledge of the time, the elusive infinitesimal of now dissolves into a scattering flock of nanoseconds. Bound by the speed of light and the velocity of nerve impulses, our perceptions of the present sketch the world as it was an instant ago, for all that our consciousness pretends otherwise, we can never catch up. Even in principle, perfect synchronicity escapes us. Relativity dictates that, like a strange syrup, time flows slower on moving trains than in the stations and faster in the mountains than in the valleys. The time for our wristwatch is not exactly the same as the time for our head. It is roughly 7:04 p.m.

Real Time The pace of living quickens continuously, yet a full understanding of things temporal still eludes us
That Mysterious Flow From the fixed past to the tangible present to the undecided future, it feels as though time flows inexorably on. But that is an illusion
Is Time an Illusion? The concepts of time and change may emerge from a universe that, at root, is utterly static
A Hole at the Heart of Physics Physicists can't seem to find the time—literally. Can philosophers help?
How to Build a Time Machine It wouldn't be easy, but it might be possible
Time and the Twin Paradox Does time tick by at the same rate for everyone?
Times of Our Lives Whether they're counting minutes, months or years, biological clocks help to keep our brains and bodies running on schedule
Remembering When Several brain structures contribute to "mind time," organizing our experiences into chronologies of remembered events
Clocking Cultures What is time? The answer varies from society to society
A Chronicle of Timekeeping Our conception of time depends on the way we measure it
From Instantaneous to Eternal The units of time range from the infinitesimally brief to the interminably long. The descriptions given here attempt to convey a sense of this vast chronological span
Ultimate Clocks Atomic clocks are shrinking to microchip size, heading for space—and approaching the limits of useful precision
How Time Flies Recent experimental optical clocks are so precise that even a small change in elevation or velocity makes them register the passage of time differently
Inconstant Constants Do the inner workings of nature change with time?
The Myth of the Beginning of Time String theory suggests that the big bang was not the origin of the universe but simply the outcome of a preexisting state
What Keeps Time Moving Forward? A timely conversation with physicist Sean M. Carroll about how our one-way trip from the past to the future is entangled with entropy and the origin of the universe
Atoms of Space and Time We perceive space and time to be continuous, but if the amazing theory of loop quantum gravity is correct, they actually come in discrete pieces
Could Time End? Yes. And no. For time to end seems both impossible and inevitable. Recent work in physics suggests a resolution to the paradox
The Science of Perception
Introduction Who says science isn't fun? Visual illusions, such as the dozens you will find in this special issue, make great eye candy. But they also serve a serious purpose for researchers. How? Illusions push the mysterious and wondrous brain into revealing its secrets.

From the confusing and fragmentary inputs gathered by our senses, our brains create our seemingly fluid conscious perceptions and a sensible narrative of the world around us. Brains do not, however, talk to us about how they perform those impressive tasks. Scientists can learn a lot by using imaging equipment and by making other observations. But sometimes they also have to "trick" brains, the better to probe perception. That's where illusions come in.

The Neuroscience of Illusion How tricking the eye reveals the inner workings of the brain
A Perspective on 3-D Visual Illusions What the leaning tower and related illusions reveal about how your brain constructs 3-D images
The Neuroscience of Yorick's Ghost and Other Afterimages Staring at images can temporarily reset retinal cells and cause ghostly visions
Colors Out of Space Colors can change with their surroundings and spread beyond the lines
What's in a Face? The human brain is good at identifying faces, but illusions can fool our "face sense"
The Eyes Have It Eye gaze is critically important to social primates such as humans. Maybe that is why illusions involving eyes are so compelling
The Illusions of Love How do we fool thee? Let us count the ways that illusions play with our hearts and minds
Art as Visual Research: Kinetic Illusions in Op Art Art and neuroscience combine to create fascinating examples of illusory motion
Sculpting the Impossible: Solid Renditions of Visual Illusions Artists find mind-bending ways to bring impossible figures into three-dimensional reality
Food for Thought: Visual Illusions Good Enough to Eat Face or food? The brain recognizes edible artwork on multiple levels
Earth 3.0 Jun2009
Introduction The climate challenge just became a lot more challenging. We know that man-made carbon dioxide emissions are accelerating global warming. But intrepid research has revealed an additional sinister threat: methane. As Sarah Simpson reports on page 30, the warming of the Arctic is releasing vast quantities of methane that has been locked away for centuries in formerly frozen soil. Once released, methane traps 25 times more heat in the atmosphere than carbon dioxide does. So it is more imperative than ever to slash greenhouse gases quickly, to slow the venting of methane.

The single boldest stroke must come from Congress. The House and Senate are debating legislation that would impose either a cap-and-trade system or a tax on carbon emissions (for updates see Certain politicians and CEOs are trying to talk Congress out of it. Our representatives should dismiss the detractors and pass legislation, before November. That deadline is crucial: nations will meet in December in Copenhagen to hammer out new international agreements to limit emissions. The U.S., shamefully, has never signed such a protocol, and leaders worldwide have said, plainly, that the Copenhagen talks will fail if the U.S. does not enact legislation to clean up its own backyard.

Another bold stroke would be to confront the 800-pound gorilla in the room: population. Cutting our wanton consumption will reduce emissions in the short term, but sustaining our planet long-term will depend on how fast population grows. It's a touchy subject, but we have to face it. Robert Engleman lays out the issues on page 22.

Hope lies in action. Let's embrace what forward-thinking economists are saying, that putting a cap or tax on carbon will stimulate massive innovation in the next great global industry: clean energy technology. Even a slowly growing population will create big demand for clean energy, and the U.S. can build a new economy by dominating this market—but only if it acts boldly, before other nations do.

Inspirations Cooking Goes Solar; Replacing the Honeybee; Teach-In Solutions; Coral Fights Antibiotic Resistance; Flatulence Fighter; Power from Potholes; Bamboo Bikes Grow; Old Circuit Boards Hit the Road; Turbines Spin in Antarctica; Greenest Skylines; Top 100 Eco-Barons; Paperless Books: A Step Closer
View: Hidden Truths Revealed U.S. Energy Flow
Front Lines Breeding Better Crops; End Double Jeopardy; Think Global, Think Local; Don't Forget Air Pollution; It's Time for Ocean Zoning
Population & Sustainability Reversing the rise in human numbers is the most overlooked and essential strategy for achieving long-term balance with the environment. Contrary to widespread opinion, it does not require "population control"
The Peril Below the Ice The melting Arctic is releasing vast quantities of methane. How big is this greenhouse threat? What can be done?
Top 25 Green Energy Leaders Forward-thinking companies, universities and municipalities are finding creative ways to run on renewable power
The Persistent Prophet Lester Brown, at times ridiculed, has been warning the world for 40 years about coalescing energy, food and population crises. So why is he optimistic now?
Can Captured Carbon Save Coal? Extracting carbon dioxide from power plant exhausts and storing it underground may be the only hope to avoid a climate change catastrophe from burning fossil fuels
Bamboo Boom It's not just for tiki torches anymore, but does this wood substitute really make for greener floors, clothing and other products?
Ca$h for Clunkers "Hey! Trade in your old, soot-spewing car for a newer one. Free." The latest scam? Not according to a former vice chair of the Federal Reserve
Cycling the World See, hear and smell the earth's joys as you ride
The Real Price of Flowers The right varieties grown in the right places leave a far smaller environmental footprint
Your Sexual Brain

How deluded we are. We believe that, with our seemingly all-knowing consciousness, we are masters of our own domain (as Jerry Seinfeld so colorfully put it). In reality, as you will learn in this special issue, the imperatives and influences of sex, the sexes and sexuality all subconsciously shape our behavior in countless ways.

If you think your conscious intellect was at work in choosing your romantic partner, for instance, think again. In his feature article "Sex and the Secret Nerve," R. Douglas Fields explains how a little appreciated cranial nerve may be pulling your strings: "Many scientists believe that pheromones, those silent chemical messengers exchanged by members of the opposite sex in search of mates, relay subconscious signals to the brain through this obscure nerve." Our kisses, too, transmit emotional messages that can cement a new relationship--or cause us to end it, as Chip Walter writes in "Affairs of the Lips.".

People make jokes about the opposing worldviews of "Mars" and "Venus." But male and female brains really are distinct in their architecture and thinking patterns. "His Brain, Her Brain," by Larry Cahill, explains how the sexes differ--and what it means. Men and women may still never understand one another, but at least now we will know why.

Choosing a partner is one thing, but how about your sexuality? Probably not, asserts Robert Epstein in "Do Gays Have a Choice?" The story begins on page 62. Same-sex preference is no biological accident of humanity, either. Find out more in "Bisexual Species," by Emily V. Driscoll.

Of course, if you would rather avoid all this tedious thinking about the subliminal power of sex, there is a cure. As Martin Portner relates in "The Orgasmic Mind," science has shown that sexual climax involves more than heightened arousal: it also requires that critical areas of the brain literally shut down. Sex makes empty-headed puppets of us all.

Bonobo Sex & Society The behavior of a close relative challenges assumptions about male supremacy in human evolution
Disturbing Behaviors of the Orangutan Studies of these great apes show that some males pursue an unexpected and disquieting evolutionary strategy
Bisexual Species Homosexual behavior is surprisingly common in the animal kingdom. It may be adaptive--helping animals to get along, maintain fecundity and protect their young
The Orgasmic Mind Achieving sexual climax requires a complex conspiracy of sensory and psychological signals--and the eventual silencing of critical brain areas
Sex and the Secret Nerve Could a little-known cranial nerve be the route by which human pheromones turn us on?
His Brain, Her Brain It turns out that male and female brains differ quite a bit in architecture and activity. Research into these variations could lead to sex-specific treatments for disorders such as depression and schizophrenia
Affairs of the Lips Researchers are revealing hidden complexities behind the simple act of kissing, which relays powerful messages to your brain, body and partner
The Truth About Online Dating The hype is huge, and the findings are disturbing--but the future of online dating looks good
Do Gays Have a Choice? Science offers a clear and surprising answer to a controversial question
Why Do Men Buy Sex? Some researchers say johns seek intimacy on demand; others believe that these men typically want to use and dominate women
Abnormal Attraction Most people are repulsed by the idea of sex with children. But keeping children safe from pedophiles means trying to discover how this disastrous craving comes about--and how to tame it
Misunderstood Crimes Once a sex offender, always a sex offender?
Earth 3.0 Mar2009

It's happening again. In the 1970s, when oil prices soared, Americans started pursuing alternative energy technologies. But when prices subsequently dropped, so did the promising projects. As recently as six months ago consumers, CEOs and politicians were hell-bent for green technologies, but then the recession worsened, oil prices plummeted and calls rose to postpone clean tech options.

Begging off now would be a terrible waste. In an incredibly short time, impressive business, technological and political gains have been made. Venture capital investment in clean tech hit an all-time high in 2008. Airlines are making test flights powered by biofuels. And President Barack Obama--exploiting unprecedented political will to clean up the planet--has promptly set the federal government on a course to confront climate change.

The U.S. and the rest of the world cannot cave in to a temporary dip in energy prices and the economy. Rest assured, both will rise again. Fossil-fuel dependence remains a grave problem: production cutbacks by the Organization of the Petroleum Exporting Countries were already pushing oil prices back up in January. Global warming still looms as highly dangerous, in part because China has announced it will increase coal production by 30 percent by 2015 to meet its energy needs.

Clearly, we should continue to pursue clean technology aggressively, if for no other reasons than to create millions of jobs and to put the country in a strong competitive position. Even venture capitalists, whose sole metric is profit, say we must stay on the offense. As John Doerr, partner at Kleiner Perkins Caufield & Byers, writes, the best response to our concurrent economic, climate and energy security crises “is a bold, coordinated campaign of investment and incentives to accelerate green innovation.” Let’s press on toward solutions for sustainable progress.

Inspirations Chestnut Trees Return; A New Aid for Elephants; Charging Ahead; Masters of Sustainability; No Recession for Green; Slippery Surfaces Save Energy; Bike-Friendlier with Facebook; Bright Lights, Clean Water; Forecasting Malaria; Efficient Power in Any Wind
View: Hidden Truths Revealed Sustaining Humanity
Front Lines The Green Road to Prosperity; More Sustainable Cities; Time to Think Hydro; Beware of Warming Sickness; Financing Energy Efficiency; Clean Tech: Force It or Fund It?
Winning the Carbon Game How Obama and his team can pass climate legislation and reach an international accord by December 2009
Saving the Ogallala Aquifer The massive underground water source feeds the middle third of the country but is disappearing fast. Can it be conserved?
Top 10 Myths About Sustainability Even advocates for more responsible, environmentally benign ways of life harbor misunderstandings of what "sustainability" is all about
The Next Generation of Biofuels Companies are poised to go commercial with gasoline substitutes made from grass, algae and the ultimate source: engineered microorganisms
Giving the Grid Some Backbone The U.S. needs a high-voltage transmission system to deliver plentiful energy from wind and sunshine to power-hungry cities. At least one plan has emerged
Arctic Landgrab Nations scramble to claim their share of the petroleum riches trapped deep within the Arctic seabed as global warming loosens that ocean’s icy grip on its bounty
Companies Pull the Climate Lever Businesses can influence government action on climate in many ways—as long as they start by building their own environmental credibility
Green Fuels for Jets Commercial airlines are testing plant-derived jet fuels that do less damage to the environment
Gone Hunting (with a Camera) Photo safaris offer excitement and beauty
The Low-Carbon Diet A California chef and a climate scientist present a recipe for sustainable eating
Earth 3.0 Dec2008
Introduction Aggressive optimism. Those two words capture the spirit of this magazine and, we hope, the spirit that Washington, D.C., will bring to urgent energy, environment and sustainability issues. Right now a new president is calculating his administration's first steps. If he is serious about ending U.S. dependence on oil, stopping climate change and reversing destruction of land and sea, he has to take strong actions in his first 100 days. In this issue, Shirley Ann Jackson, president of Rensselaer Polytechnic Institute, talks straight about what those actions should be.

One big decision will be how to limit carbon dioxide emissions. Everyone has been calling for a cap-and-trade system, but as entrepreneur Peter Barnes of the Tomales Bay Institute explains, such an approach has a tragic flaw: it will cost average citizens money. Barnes has a better plan, called cap and dividend, that actually pays you and me.

Like it or not, money is at the nexus of energy and emissions decisions. History shows that as soon as high fossil-fuel prices drop, so does investment in alternative energy. Economist Steven Kyle of Cornell University argues there is only one way to prevent a backslide: a tax on oil. If you think altruism or fear is enough to support clean energy, talk to venture capitalists. I recently asked three of them whether, knowing the national security and environmental value of weaning society off oil, they would continue to fund alternative energy start-ups if oil prices sagged. All three said no.

Given that, the government has to step in. It needs to stop subsidizing fossil industries and start funding renewable ones, even if standard economic models question such spending. A century ago the federal government backed a struggling electric grid and a fledgling automobile industry, despite models that indicated a poor probability of payback. Of course, those bold actions fueled American prosperity for decades. The lever then, as now, was neither a cost-benefit analysis nor hand-wringing but the political will to embrace aggressive optimism and lead.

Inspirations Crops Could Cleanse Soil; Intel Saves Air and Money; You, Too, Can Be a Hypermiler; Unselling Bottled Water; Wanted: Spare Computer Power; Greening the Supply Chain; Stock-Market Strategy Halts Fishing Collapse; Rooftop Solar on a Roll; Organic Farms Say “WWOOF”; Singing in the Rain (Forest)
View The profusion of paper bags. Vanishing mammals. Plastic in the Pacific
Front Lines Obama's First 100 Days; Cap and Dividend, Not Trade; A Move to Green-Collar Jobs; Keep Oil Prices High, Please; Confronting Videophilia; Exploiting the Shame Meter
Can Nuclear Power Compete? Newly approved reactor designs could reduce global warming and fossil-fuel dependence, but utilities are grappling with whether better nukes make market sense
China's Energy Paradox China is aggressively building cleaner cities and renewable power supplies, but the relentless expansion of dirty coal may suffocate those efforts. A firsthand look
The Need to Lead in Clean Tech An interview with Thomas L. Friedman
Chicago Goes Green Mayor Richard Daley has unveiled an aggressive plan to transform the old, gritty city. If he can pull it off, other cities might follow
Carbon Cowboys Ranchers in Montana are being paid by polluters to let the grass grow
Sharking Guadalupe Ecotourism has become the unlikely protector of an unexpectedly endangered species: the great white
Regrowing Borneo, Tree by Tree To save orangutans, scientist Willie Smits is restoring a rain forest—and creating new livelihoods for the Indonesian families who help him
Turning the Tide Several companies are trying to convert experimental ocean energy plants into commercial powerhouses
The Behemoth and the Butterfly Experience the awe of mass migrations
Earth 3.0
Introduction The "Earth" part of the title of this special issue from Scientific American is no doubt self-explanatory, but why "3.0"? Because this planet is no longer simply the home of our species: it is also our creation. And as with any product, sometimes it is prudent to upgrade its quality.

If you will indulge the analogy further, Earth 1.0 was the world that persisted and evolved for billions of years, up until very recently. The environment was dominated by closed ecological loops and a few geological and astronomical processes, such as the movements of continents and the brightness of the sun. As such, life was highly sustainable. Even after we humans developed agriculture, which considerably enlarged our footprint on the environment, our overall influence was fairly small and localized.

That changed two centuries ago with the arrival of Earth 2.0, when the industrial revolution gave the human race the leverage to achieve unprecedented health and prosperity but at the price of wanton consumption of natural resources. Today we have unwittingly become the major drivers of potentially disastrous climate change. We have extinguished species at a rate not seen since the end of the dinosaurs. We have depleted ocean fisheries so severely they could collapse by midcentury. And yet much of the human population still suffers awful poverty and lack of opportunity.

Earth 3.0 is thus the new way forward that we need to establish, one with all the prosperity of 2.0 but also the sustainability of 1.0. And it is in that spirit that we present this issue, which explores and celebrates opportunities for both economic and environmental progress.

Building a better future for ourselves and the rest of the planet is possible, but it will involve action--sometimes drastic action--at every level of society, from elected officials and CEOs to individual consumers. Decisions will need to be informed by knowledge of the relevant underlying science and the available technologies. The right solutions will address both environmental problems and concerns about economic development rather than sacrificing one for the sake of the other.

We are proud to offer Earth3.0 as a tool for promoting the awareness and discussions that can encourage progress.

Inspirations Perma-Vault Now Accepting Seeds; Dark Horse: Oil from Algae; Florida's Garbage Vaporized; Green Funds Remain Hot; Alexandra Cousteau Wades In; United under 1Sky; China Targets Cleaner Coal; Jack Johnson's Low-Impact Tour; One Brick Powers All; Preserving Forests and Business
View Two million bottles every five minutes. Appalachians clear-cut for coal. Fuel-efficiency race
Front Lines One Last Chance to Lead; The Other CO2 Problem; Learning from the Internet; Green Jobs, Not Jails; Biofuels or Food?; Plastics in Our Diet
Catch-22: Water vs. Energy Water is needed to generate energy. Energy is needed to deliver water. Both resources are limiting the other—and both may be running short. Is there a way out?
Are Hotspots the Key to Conservation? Preserving biodiversity in rich habitats is good. But global warming and other new threats may call for a new strategy
For Security, Get Off Oil Former CIA director R. James Woolsey says America’s oil dependence is a grave threat
MisLEEDing? Constructing buildings to the LEED standard can conserve energy and materials—or be exploited for promotional gain
Beyond the Tipping Point The world’s most outspoken climatologist argues that today’s carbon dioxide levels are already dangerously too high. What can we do if he is right?
Eco-Cities of the Future Massive developments proposed for the U.S., China and Abu Dhabi aim to reduce or even eliminate the environmental cost of city living
Growing Vertical Cultivating crops in downtown skyscrapers might save bushels of energy and provide city dwellers with distinctively fresh food
Fuel Cell Cars Two street-legal models provide a nice ride
Voluntourism Rocks Take a trip. Roll up your sleeves. Have fun
New Answers for Cancer
Introduction Nearly 40 years since we declared war on cancer, how goes the campaign against this intractable and ancient adversary? As you will learn in this special edition, our enemy intelligence has improved over the years, enabling us to get a better bead on where the trouble begins. And we have developed stronger weapons, to more precisely pursue and annihilate diseased tissue.

Finding Enemy Forces. Cancer's origins are multifaceted, a combination of an individual's genetic factors and influences from the surrounding environment and his or her personal history and lifestyle. Even stem cells--which, in other contexts, offer promise for the treatment of a variety of ailments--could be to blame.

Destroying the Targets. While scientists are grappling to gain a better understanding of cancer's complex beginnings, they also have improved ways of stalling the advance of the disease.

Hope in the Trenches. Patients with cancer, empowered by expanding informational resources and the changing, more open attitudes of doctors, are living longer and better than ever today. Although medicine clearly has much work to do, with advances occurring rapidly, we are on the path to managing this chronic disease.

Living with Cancer Keep up your spirits and tap available resources to make the disease manageable
Evolved for Cancer? Natural selection lacks the power to erase cancer from our species and, some scientists argue, may even have provided tools that help tumors grow
Mapping the Cancer Genome Pinpointing the genes involved in cancer will help chart a new course across the complex landscape of human malignancies
Untangling the Roots of Cancer Recent evidence challenges long-held theories of how cells turn malignant--and suggests new ways to stop tumors before they spread
Stem Cells: The Real Culprits in Cancer? A dark side of stem cells--their potential to turn malignant--is at the root of a handful of cancers and may be the cause of many more. Eliminating the disease could depend on tracking down and destroying these elusive killer cells
A Malignant Flame Understanding chronic inflammation, which contributes to heart disease, Alzheimer's and a variety of other ailments, may be a key to unlocking the mysteries of cancer
The Long Arm of the Immune System Dendritic cells catch invaders and tell the immune system when and how to respond. Vaccines depend on them, and scientists are even employing the cells to stir up immunity against cancer
Taming Vessels to Treat Cancer Restoring order to the chaotic blood vessels inside a tumor opens a window of opportunity for attacking it. Surprisingly, drugs meant to destroy vasculature can make the repair and may help reverse conditions that lead to cardiovascular disease and blindness
Tumor-Busting Viruses A technique called virotherapy harnesses viruses, those banes of humankind, to stop another scourge--cancer
New Light on Medicine Pigments that turn caustic on exposure to light can fight cancer, blindness and heart disease. Their light-induced toxicity may also help explain the origin of vampire tales
Gaining Ground on Breast Cancer The newest targeted therapies are helping doctors to tailor increasingly effective treatments to individual patients
105 Mind-Bending Illusions
Introduction "The camera does not lie," the saying goes. And we tend to think of our eyes and our other sensory organs as video equipment, faithfully recording all the details of our busy lives. As you will learn from the articles on illusions collected in this special issue, however, we see with our brains, not with our eyes. And our brains make instant value judgments about the jumble of incoming sensory information, depending on what is important at that moment to us, to create a sensible narrative of the world around us.

Rather than pondering every bit of light that enters our orbs, the brain quickly jumps to conclusions, based on millions of years of evolution. Humans are intensely visual creatures, and we have developed an incredible apparatus for detecting things that are critical to our survival, such as predators, prey and mates. For instance, we can instantly mentally assemble several tiny patches of orange with stripes peeking through dense foliage: "tiger!" As we glance around a room, the image bounces on the retina (the light-receiving tissue at the back of the eye) as various areas of the scene excite different groups of cells. Yet the world appears stable to us, the view a smooth pan across our surroundings. The brain even fills in missing bits of picture in the eye's blind spot, where the optic nerve pierces the retina.

On the other hand, we do not see everything. Something that is irrelevant to a particular task will not make it to our conscious awareness. In one telling experiment, volunteers had to count how many times a basketball got passed between players. A person in a gorilla suit then strutted across the room. Concentrating on those ball passes, about half the volunteers did not see the gorilla.

Of course, the brain cannot actually tell us about what it is thinking as it processes sensory inputs, focusing on certain items and ignoring others. But our responses to illusions can be just as revealing. Scientists have long used these disarmingly simple--and fun--sensory tricks to probe the mind's inner workings. This special edition offers an amazing collection of such illusions and the lessons that they teach us about the brain. We can promise you one thing: you won't believe your eyes.

Mind the Gap The brain, like nature, abhors a vacuum
Stability of the Visual World When your eyes scan a room, why doesn't the world appear to bounce like the real image on your retina?
When the Two Eyes Clash A tale of binocular rivalry
How Blind Are We? We have eyes, yet we do not see
Hidden in Plain Sight Camouflage in fish and other animals provides insights into visual perception
Right Side Up Studies of perception show the importance of being upright
Seeing Is Believing 2-D or not 2-D, that is the question: test yourself to learn what shapes formed by shading reveal about the brain
Seeing in Black & White Why it's not so cut-and-dried
Transparently Obvious How the brain sees through the perceptual hurdles of tinted glass, shadows and all things transparent
The Reality of Illusory Contours How can an imaginary square look more real than a box with actual lines?
The Quirks of Constancy Even when we consciously know two lines are the same length, why can't we help seeing them as different?
Sizing Things Up When you hoist two items of equal weight, your brain may be doing some heavy lifting
A Moving Experience How the eyes can see movement where it does not exist
Ambiguities & Perception What uncertainty tells us about the brain
Touching Illusions Startling deceptions demonstrate how tactile information is processed in the brain
The Phantom Hand The feeling of being touched on a fake hand illuminates how the brain makes assumptions about the world
It's All Done with Mirrors Reflections on the familiar and yet deeply enigmatic nature of the looking glass
Paradoxical Perceptions How does the brain sort out contradictory images?
The Neurology of Aesthetics How visual-processing systems shape our feelings about what we see
Cracking the da Vinci Code What do the Mona Lisa and Abraham Lincoln have in common?
Illusory Color & the Brain Novel illusions suggest that the brain does not separate perception of color from perception of form and depth
Your Future with Robots
Introduction They have been part of our collective imagination almost since we began to set down words. Mechanical beings sparked to life in the myths of ancient Greece, the Middle East, China and the Nordic countries. Today we call them robots--from robota, meaning "drudgery" or "hard work" in Czech and related languages. As that name implies, so far these useful machines have been limited in their applications to the sorts of repetitive tasks best suited to automatons--tirelessly turning screw after screw in a factory assembly line, for instance.

Now robots are beginning to enter our lives in much more personal ways. Already robo-vacuums such as the Roomba are easing housework, and digital pets such as Tamagotchis and the e-dog Aibo are serving as electronic companions. Experts envision far more in the short years ahead. Bill Gates writes in his feature article "A Robot in Every Home," of nothing less than a transformation of domestic life. It is only a matter of time. After all, he adds: "Some of the world's best minds are trying to solve the toughest problems of robotics, such as visual recognition, navigation and machine learning." Two million personal robots were in use worldwide in 2004, and seven million more will be installed by this year, according to one estimate.

To expand further, they will require adaptive, complex processors, as Hans Moravec describes in "Rise of the Robots." By 2050 robot "brains" that execute 100 trillion instructions per second will start to rival human intelligence. Robots will also need to become more physically flexible and adaptable. In "Artificial Muscles," Steven Ashley describes springy polymers that could even produce power with movement.

At the same time that robots will be acquiring more human attributes, people will be adopting electronic implants to improve skills such as memory, according to "The Coming Merging of Mind and Machine," by Ray Kurzweil. We will also be using the power of thought to direct machines, say Miguel A. L. Nicolelis and John K. Chapin in "Controlling Robots with the Mind." Indeed, the differences between maker and creation grow less distinct all the time.

A Robot in Every Home The leader of the PC revolution predicts that the next hot field will be robotics
Rise of the Robots By 2050 robot brains based on compu_ters that execute 100 trillion instructions per second will start rivaling human intelligence
The Coming Merging of Mind and Machine The accelerating pace of technological progress means that our intelligent reations will soon eclipse us--and that their reations will eventually eclipse them
Robots vs. Humans: Who Should Explore Space? Unmanned spacecraft are exploring the solar system more cheaply and effectively than astronauts are. Astronaut explorers can perform science in space that robots cannot
An Army of Small Robots For robot designers these days, small is beautiful
Swarm Smarts "Using ants and other social insects as models, computer scientists have created software agents that cooperate to solve complex problems, such as the rerouting of traffic in a busy telecom network
Go Forth and Replicate Birds do it, bees do it, but could machines do it? Computer simulations suggest that the answer is yes
Ballbots A new mode of locomotion will enable mobile robots to stand tall and move gracefully through busy everyday environments
Artificial Muscles Novel motion-producing devices--actuators, motors, generators--based on polymers that change shape when stimulated electrically are reaching commercialization
Controlling Robots with the Mind People with nerve or limb injuries may one day be able to command wheelchairs, prosthetics, and even paralyzed arms and legs by "thinking them through" the motions
Innovations from a Robot Rally The Grand Challenge competition spurred advances in laser sensing, computer vision and autonomous navigation--not to mention a thrilling race for the $2-million prize
Scientific American Body
Introduction Throw the word "health" at Google, and you will retrieve, as I write this, about 958 million results. Alternatively, if you feel up to reading them, you could directly consult the medical journals for information; the National Library of Medicine's MEDLINE service indexes about 5,000 of them. If you are into health and fitness magazines, you probably have more than 100 of those to choose from.

Clearly, a world of health information is out there and readily available if you want it. The problem is one of navigating through it to worthy destinations. Finding your way to relevant, trustworthy information, presented in terms that are not only understandable but appealing to your interests, is still a challenge.

That is why we dare to think the magazine you hold in your hands, Scientific American Body, has something special to offer to the curious health consumer. Scientific American has been covering new developments in medicine, science and technology for more than 162 years. It brings together leading health professionals and experienced journalists to explain the significance of new discoveries, the state of current knowledge and the bright possibilities just coming over the horizon. And as the realm of knowledge about health and medicine continues to expand, Scientific American is proud to present new offerings in print and online to keep you informed about it.

We believe that sophisticated health readers want more than a service-oriented breakdown of what to eat, what drugs to take and how to exercise. Scientific American Body therefore brings you just enough of the science underlying health recommendations for you to draw your own conclusions about their solidity or even their safety. Yet we also realize that health and wellness is not purely a matter of medical science--that there is an artistry to healing that needs to take into account the whole of a person. Thus, Body also includes voices of personal testimonial, discussing their own experiences with illness, recovery and prevention. We are also eager to take a clear-eyed look at the state of alternative medicine and to hail it for its successes or to criticize it for its failures, depending on what the data show.

Not Just a Pump The goal of building a safe artificial heart has frustrated bioengineers for more than four decades. At last, an end could be in sight. (With additional contributions from Steve Ditlea and Mark Fischetti)
Testosterone's Bad Rep Hormones don't necessarily make men violent, but they do cause them to seek social dominance
The Skinny on the Environment The very structure of our communities may predispose us to inactivity and obesity. Now researchers are remodeling cities for healthier kids
Getting to Know Nutraceuticals Claims for some of these food-based dietary supplements stand up to scientific scrutiny, but others falter
Managing Diabetes Globally, 171 million people have the disease, and that number is exploding. But lizard spit, new monitors and other drugs and devices can help control diabetes better than ever
Is There Really an Autism Epidemic? The public's alarm stems from misundersatnding of statistics on autism
Saving Troubled Knees Silk scaffolds, grafts from pigs and green tea extracts might someday help keep injured and vulnerable joints active
Where Is the AIDS Vaccine? Science gets closer, but a fully effective vaccine against HIV remains elusive
The Ultimate Blood Test A pricey way to determine health risks: take 250 tests at once
Five New Year's Resolutions You Owe Yourself This December 31st, make yourself some life-enhancing promises
The Rise of Nanotech
Introduction If you have heard about nanotechnology at all, you may be aware of its science-fiction-sounding hype. Proponents picture a future in which tiny bots would magically repair tissue to prolong our life span. On the dark side is the disturbing vision of "gray goo," where self-replicating nanodevices destroy the planet. The reality of the burgeoning field of nanotech, however, is hardly less startling in its transformative potential. Some have proclaimed it "the next industrial revolution."

"Nanotechnology" broadly applies to control of materials and components only a few billionths of a meter in size. Already manufacturers sell several hundred products that use nanotech, mainly skin lotions. Next up are advances in biotechnology and electronics--and a merging of the two.

Consider, for instance, molecular building blocks called bis-amino acids, which chemists string together into protein-like structures. Applications include medicines, enzymes for catalyzing reactions, sensors, nanoscale valves and computer storage devices. Other researchers are using natural molecular machines to process information: they receive input from other biological molecules and output a tangible result, such as a signal or a therapeutic drug.

Nanoscience advances are pushing traditional electronics in new directions as well. George Gruner describes applications that encompass sensors, solar cells, electronic paper and bendable touch screens. Imagine a morning "paper" with headlines that change as news breaks.

Or how about an invisibility cloak? Harry A. Atwater explains how optical signals squeeze through minuscule wires, producing so-called plasmons. Plasmonic circuits could help to move lots of data and improve the resolution of microscopes, the efficiency of light-emitting diodes, and the sensitivity of detectors. Such materials could alter the electromagnetic field around an object to such an extent that it would become invisible. The nanoregime offers enormous promise indeed.

Plenty of Room Indeed There is plenty of room for practical innovation at the nanoscale. But first, scientists have to understand the unique physics that governs matter there
The Art of Building Small Researchers are discovering cheap, efficient ways to make structures only a few billionths of a meter in size
Molecular Lego A modest collection of small molecular building blocks enables the design and manufacture of nanometer-scale structures programmed to have virtually any shape desired
Nanotechnology and the Double Helix DNA is more than just the secret of life--it is also a versatile component for making nanoscopic structures and devices
Bringing DNA Computers to Life Tapping the computing power of biological molecules gives rise to tiny machines that can speak directly to living cells
Carbon Nanonets Spark New Electronics Random networks of tiny carbon tubes could make possible low-cost, flexible devices such as "electronic paper" and printable solar cells
The Promise of Plasmonics A technology that squeezes electromagnetic waves into minuscule structures may yield a new generation of superfast computer chips and ultrasensitive molecular detectors
The Incredible Shrinking Circuit Researchers have built nanotransistors and nanowires. Now they just need to find a way to put them all together
Less Is More in Medicine Sophisticated forms of nanotechnology will find some of their first real-world applications in biomedical research, disease diagnosis and, possibly, therapy
Shamans of Small Like interstellar travel, time machines and cyberspace, nanotechnology has become one of the core plot devices on which science-fiction writers draw
The Early Years
Introduction A child's rapid cognitive development begins from the earliest ages and may continue into young adulthood. Before they can talk, tots are learning how the world works and how they can apply that knowledge. "Test Subjects in Diapers," by Gisa Aschersleben, reveals how quickly infants learn to think critically--and the ways in which scientists can "ask" babbling babies to show what they know.

Knowledge about a child's rapid mental development also serves to emphasize the importance of early intervention in cases where children have special needs. Articles in the issue explore faster detection of disorders and possible therapies for children with autism, ADHD and Down syndrome.

When does the brain finish "growing up"? Many neuroscientists say that cognitive development, especially in areas of the brain that are associated with decision making and other "executive" functions, continues into the second decade of life, reports Leslie Sabbagh in "The Teen Brain, Hard at Work." Meanwhile psychologist Robert Epstein warns against excess reductionism in applying imaging studies of teen and adult brains to complex human behaviors. We blame teen turmoil on immature brains--but, he asks, did the brains cause the turmoil, or did the turmoil affect the brains?

As you page through the articles in the issue, we hope one thing will be clear: as we learn more about how the mind operates, we are better able to help children grow up to lead happy, fulfilling lives.

Big Answers from Little People In infants, Elizabeth Spelke finds fundamental insights into how men and women think
Test Subjects in Diapers When do babies recognize the intentions of others--and become capable of deliberate actions themselves?
Detecting Autism Early New techniques could diagnose autism in babies, enabling more effective treatment while the brain is most malleable
Broken Mirrors: A Theory of Autism Studies of the mirror neuron system may reveal clues to the causes of autism and help researchers develop new ways to diagnose and treat the disorder
Mindful of Symbols On the way to learning that one thing can represent another, young children often conflate the real item and its symbol. These errors show how difficult it is to start thinking symbolically
Informing the ADHD Debate The latest neurological research has injected much needed objectivity into the disagreement over how best to treat children with attention-deficit disorders
Just a Bit Different With special training early in life, children born with Down syndrome have a higher chance of developing into independent individuals
Stopping the Bullies School can be torture for children who are targeted by abusive students
The Teen Brain, Hard at Work Under challenging conditions, adolescents may assess and react less efficiently than adults
Is the Teen Brain Too Rational? With the decision-making areas of their brains still developing, teenagers show poor judgment in risky situations. Thinking less logically may be the answer
The Myth of the Teen Brain We blame teen turmoil on immature brains. But did the brains cause the turmoil, or did the turmoil shape the brains?
Train Your Brain Mental exercises with neurofeedback may ease symptoms of attention-deficit disorder, epilepsy and depression--and even boost cognition in healthy brains
Reality-Bending Black Holes
Introduction Black holes curve the fabric of spacetime so extremely that it rends. The superdense objects devour anything--even light--that strays too close, a trip from which there is no escape. Perhaps their most singular power, however, is their hold on our imagination. Learning more about these implacable gluttons offers the same shivery frisson as watching a stalking horror-movie creature while knowing we are safe in our cushioned seats.

Black holes offer much more to science than the can't-look-can't-look-away spectacle of destruction. The forces they unleash shape the regions around them, providing clues to the evolution of stars and galaxies. For instance, the dark sinkholes reveal a surprising bright side. In their quest to solve an enduring mystery, astronomers have learned that black holes are responsible for some of the most dazzling fireworks in the universe. When a massive star collapses to birth a black hole, it releases a titanic pulse of radiation in a gamma-ray burst that can be seen from billions of light-years away, as Neil Gehrels, Luigi Piro and Peter J. T. Leonard discuss in their article, "The Brightest Explosions in the Universe." Greedily feeding supermassive black holes also exist in regions called starbursts, where stars are forming at a phenomenal rate. How? Turn to "The Galactic Odd Couple," by Kimberly Weaver.

Studying black holes yields insights into other mind-bending areas of physics. In the coming years the highest-energy particle accelerators on earth might be able to produce distant cousins of the astrophysical behemoths: microscopic black holes. They would explode immediately after they formed, giving clues about how spacetime is woven together and whether it has unseen higher dimensions, explain Bernard J. Carr and Steven B. Giddings in "Quantum Black Holes." Still other features in the issue explore what black holes can tell us about time travel, the nature of gravity, the ultimate amount of information the universe can hold and whether our seemingly 3-D reality is actually an illusion.

The Reluctant Father of Black Holes Albert Einstein's equations of gravity are the foundation of the modern view of black holes; ironically, he used the equations in trying to prove that these objects cannot exist
An Echo of Black Holes Sound waves in a fluid behave uncannily like light waves in space. Black holes even have acoustic counterparts. Could spacetime literally be a kind of fluid, like the ether of pre-Einsteinian physics?
Quantum Black Holes Physicists could soon be creating black holes in the laboratory
How to Build a Time Machine It wouldn't be easy, but it might be possible
The Brightest Explosions in the Universe Every time a gamma-ray burst goes off, a black hole is born
The Galactic Odd Couple Why do giant black holes and stellar baby booms, two phenomena with little in common, so often go together?
Colossal Galactic Explosions Enormous outpourings of gas from the centers of nearby galaxies may ultimately help explain both star formation and the intergalactic medium
The Midlife Crisis of the Cosmos Although it is not as active as it used to be, the universe is still forming stars and building black holes at an impressive pace
Information in the Holographic Universe Theoretical results about black holes suggest that the universe could be like a gigantic hologram
The Illusion of Gravity The force of gravity and one of the dimensions of space might be generated out of the peculiar interactions of particles and fields existing in a lower-dimensional realm
Black Hole Computers In keeping with the spirit of the age, researchers can think of the laws of physics as computer programs and the universe as a computer
Eating to Live
Introduction Even 500 years ago people had some inkling that what we eat affects our well-being. "A good coke is halfe a physycyon," wrote Andrew Boorde in 1547 in Breviary of Health. Head chefs, or majordomos, seasoned their dishes with early ideas about diet and nutrition that still influence meals today, as Rachel Laudan explains in her article, "Birth of the Modern Diet." We have been grappling with what food means for health ever since. In recent years, modern science has come to the table, gathering the many insights you'll find in this special issue.

Obviously, we need a certain minimum diet to survive. But overabundance is also a problem, as we learn in banner headline after headline about the detrimental effects on the cardiovascular system and other areas of the body. But is that so? In his article, W. Wayt Gibbs explores the question, "Obesity: An Overblown Epidemic?"

Also in the news a lot lately is the idea that cutting calories may prolong youthful vigor into old age. "Calorie Restriction and Aging," by Richard Weindruch, explains how animals that consume one-third fewer calories in studies display greater vitality than animals fed a normal diet. If the regimen sounds punishing, don't despair. "The Serious Search for an Antiaging Pill," by Mark A. Lane, Donald K. Ingram and George S. Roth, offers hope for finding a drug that mimics the effects of calorie restriction.

Amounts are one factor, but what we eat is also a critical influence on our abilities to stay strong and active into the twilight years. Science has learned much since the "four food groups" that my mother nagged me about as a child. "Rebuilding the Food Pyramid," by Walter C. Willett and Meir J. Stampfer, reviews the latest research on creating a proper diet.

Last, as the holiday season is upon us, let us make a toast to another source of vital spirits. In "Drink to Your Health?" Arthur L. Klatsky tells us how small to moderate amounts of alcohol can lend cardiovascular benefits. Cheers.

Birth of the Modern Diet Ever wonder why dessert is served after dinner? The origins of modern Western cooking can be traced to ideas about diet and nutrition that arose during the 17th century
Rebuilding the Food Pyramid Dietary guides introduced in 1992 and 2005 have led people astray. Some fats are healthy for the heart, and many carbohydrates clearly are not
Drink to Your Health? Three decades of research shows that drinking small to moderate amounts of alcohol has cardiovascular benefits. A thorny issue for physicians is whether to recommend drinking to some patients
Future Feast Even the meat and potatoes are being reinvented: the meat could come from a test tube, and the potatoes could ward off cholera
The Risks on the Table More than half the foods in U.S. supermarkets contain genetically modified ingredients. Have they been proved safe for human consumption?
Does the World Need GM Foods? Two leading figures in the debate over genetic engineering defend their stances
Seeds of Concern Are genetically modified crops an environmental dream come true or a disaster in the making? Scientists are looking for answers
Edible Vaccines One day children may get immunized by munching on foods instead of enduring shots. More important, food vaccines might save millions who now die for lack of access to traditional inoculants
Calorie Restriction and Aging Eating less--while maintaining adequate nutrition--is a recipe for longer life in many animals. Might it help humans as well?
The Serious Search for an Antiaging Pill In government laboratories and elsewhere, scientists are seeking a drug able to prolong life and youthful vigor. Studies of calorie restriction are showing the way
Unlocking the Secrets of Longevity Genes A handful of genes that control the body's defenses during hard times can also dramatically improve health and prolong life in diverse organisms. Understanding how they work may reveal the keys to extending human life span while banishing diseases of old age
Obesity: An Overblown Epidemic? Dissenting researchers accuse government and medical authorities--as well as the media--of misleading the public about the health consequences of rising body weights
Dying to Be Thin Eating disorders cripple--literally--millions of young women, in large part because treatments are not always effective or accessible
Secrets of the Senses
Introduction Imagine what it must be like. In a condition called synesthesia, senses blend, with exotic effects. Each number may evoke its own color, and flavors can mingle with shapes--in one instance letting a man tell that a roasted chicken was done, because it tasted "pointy." In their article, "Hearing Colors, Tasting Shapes," Vilayanur S. Ramachandran and Edward M. Hubbard describe how synesthesia has yielded insights into how the brain processes complex sensory inputs.

We take our conventional set of senses for granted, but their capabilities are no less astounding for their everyday qualities. The constant stream of data they provide helps the brain interpret our surroundings, giving us vital tools to survive and thrive. As Nobel Prize winner Richard Axel writes in "The Molecular Logic of Smell," humans "can recognize approximately 10,000 scents, ranging from the pleasurable scent of freshly cut flowers to the aversive smell of an angry skunk." Other senses leap into action to protect us from such foul-smelling danger. Interpreting acoustic signals from our two ears, the brain locates the rustling of an animal on the forest floor. At the same time, our visual systems near-instantly assemble into a coherent whole the scattered patches of black and white peeking through the leaves: "Skunk!"

When bereft of sensory feedback, the brain hastens to compensate, with revealing results. "Phantom Limbs," by Ronald Melzack, describes the enduring mental presence of missing appendages, whereas "How the Blind Draw," by John M. Kennedy, discusses a surprising connection between vision and touch.

As scientists try to make sense of our senses, they also seek to imitate or even improve on them to serve us in new ways. "Neuromorphic Microchips," by Kwabena Boahen, describes work to etch visual systems in silicon for better artificial-recognition technologies. Kathryn S. Brown's story, which asks "Are You Ready for a New Sensation?", explores how biology is combining with engineering to design the sensory experiences of tomorrow. These thought-provoking pieces, and the others in the issue, offer what we hope will be a sensational experience.

Vision: A Window into Consciousness In their search for the mind, scientists are focusing on visual perception--how we interpret what we see
Dying to See Studies of the lens of the eye not only could reveal ways to prevent cataracts but also might illuminate the biology of Alzheimer's, Parkinson's and other diseases in which cells commit suicide
Neuromorphic Microchips Compact, efficient electronics based on the brain's neural system could yield implantable silicon retinas to restore vision, as well as robotic eyes and other smart sensors
Listening with Two Ears Studies of barn owls offer insight into just how the brain combines acoustic signals from two sides of the head into a single spatial perception
Music and the Brain What is the secret of music's strange power? Seeking an answer, scientists are piecing together a picture of what happens in the brains of listeners and musicians
How the Blind Draw Blind and sighted people use many of the same devices in sketching their surroundings, suggesting that vision and touch are closely linked
Phantom Limbs People who have lost an arm or a leg often perceive the limb as though it were still there. Treating the pain of these ghostly appendages remains difficult
Are You Ready for a New Sensation? As biology meets engineering, scientists are designing the sensory experiences of a new tomorrow
The Molecular Logic of Smell Mammals can recognize thousands of odors, some of which prompt powerful responses. Recent experiments illuminate how the nose and brain may perceive scents
Hearing Colors, Tasting Shapes People with synesthesia--whose senses blend together--are providing valuable clues to understanding the organization and functions of the brain
Making Sense of Taste How do cells on the tongue register the sensations of sweet, salty, sour and bitter? Scientists are finding out--and discovering how the brain interprets these signals as various tastes
Becoming Human
Introduction A savvy handicapper would never have put money on the continued existence of this evolutionary dark horse. Nearly hairless, weak--no sharp claws or slicing teeth here--and slow, with a bumpy bipedal gait, humans might initially appear to be one of the unlikeliest survivors on earth. Except for the oversize brains.

So much of the rise of our ancestors from humble beginnings to today's world-dominant swell of humanity tracked the stunning growth of all that furrowed cortex. From roughly two million years to 250,000 years ago, the brain's total volume expanded by a tablespoonful every 100,000 years, estimates Harvard University biologist E. O. Wilson. If we could stretch a modern person's cortex flat, it would occupy an area the size of four sheets of standard letter-size paper. In contrast, a chimp's would cover one sheet; a monkey's, a postcard; and a rat's, a stamp.

But size alone does not explain our matchless reasoning skills. One of the mysteries of human evolution is that other species with large brains (such as Neandertals) seemingly did not achieve comparable levels of cognition. Could a cultural innovation, perhaps driven by rapid environmental changes, have contributed to the rise of symbolic thought, language and cooperative group society?

As our primate ancestors' intellects deepened, their bodies continued to morph. Their need to stoke the energy-consuming organ in their skulls with nutritious, calorie-rich fuel created selection pressure favoring features now characteristic of primates, such as grasping hands with opposable thumbs. "To a great extent," concludes Katharine Milton, "we are truly what we eat."

Even as recent discoveries answer some questions about our fascinating and complex history, they raise others. Alone among creatures alive today, we enjoy the ability to contemplate our species' odyssey through time. Food for thought.

Planet of the Apes During the Miocene epoch, as many as 100 species of apes roamed throughout the Old World. New fossils suggest that the ones that gave rise to living great apes and humans evolved not in Africa but Eurasia
Bonobo Sex and Society The behavior of a close relative challenges assumptions about male supremacy in human evolution
Diet and Primate Evolution Many characteristics of modern primates, including our own species, derive from an early ancestor's practice of taking most of its food from the tropical canopy
Why Are Some Animals So Smart? The unusual behavior of orangutans in a Sumatran swamp suggests a surprising answer
Stranger in a New Land Stunning finds in the Republic of Georgia upend long-standing ideas about the first hominids to journey out of Africa
The Littlest Human A spectacular find in Indonesia reveals that a strikingly different hominid shared the earth with our kind in the not so distant past
Founder Mutations A special class of genetic mutations that often cause human disease is enabling scientists to trace the migration and growth of specific human populations over thousands of years
How We Came to Be Human The acquisition of language and the capacity for symbolic art may lie at the very heart of the extraordinary cognitive abilities that set us apart from the rest of creation
The Morning of the Modern Mind Controversial discoveries suggest that the roots of our vaunted intellect run far deeper than is commonly believed
The Emergence of Intelligence Language, foresight and other hallmarks of intelligence are very likely connected through an underlying facility that plans rapid, novel movements
A Matter of Time
Introduction More than 200 years ago Benjamin Franklin coined the now famous dictum that equated passing minutes and hours with shillings and pounds. The new millennium--and the decades leading up to it--has given his words their real meaning. Time has become to the 21st century what fossil fuels and precious metals were to previous epochs. Constantly measured and priced, this vital raw material continues to spur the growth of economies built on a foundation of terabytes and gigabits per second.

This reduction of time to money may extend Franklin's observation to an absurd extreme. But the commodification of time is genuine--and results from a radical alteration in how we view the passage of events. Our fundamental human drives have not changed from the Paleolithic era, hundreds of thousands of years ago. Much of what we are about centers on the same impulses to eat, procreate, fight or flee that motivated Fred Flintstone. Despite the constancy of these primal urges, human culture has experienced upheaval after upheaval in the period since our hunter-gatherer forebears roamed the savannas. Perhaps the most profound change in the long transition from Stone Age to information age revolves around our subjective experience of time.

But what is time? Physicists and philosophers have grappled with the question. So, too, have biologists and anthropologists. This special issue explores their musings. --The Editors

Real Time The pace of living quickens continuously, yet a full understanding of things temporal still eludes us
That Mysterious Flow From the fixed past to the tangible present to the undecided future, it feels as though time flows inexorably on. But that is an illusion
A Hole at the Heart of Physics Physicists can't seem to find the time--literally. Can philosophers help?
How to Build a Time Machine It wouldn't be easy, but it might be possible
Time and the Twin Paradox Does time tick by at the same rate for everyone?
From Instantaneous to Eternal The units of time range from the infinitesimally brief to the interminably long. The descriptions given here attempt to convey a sense of this vast chronological span
Times of Our Lives Whether they're counting minutes, months or years, biological clocks help keep our brains and bodies running on schedule
Remembering When Several brain structures contribute to "mind time," organizing our experiences into chronologies of remembered events
Clocking Cultures What is time? The answer varies from society to society
A Chronicle of Timekeeping Our conception of time depends on the way we measure it
Ultimate Clocks Atomic clocks are shrinking to microchip size, heading for space--and approaching the limits of useful precision
Inconstant Constants Do the inner workings of nature change with time?
The Myth of the Beginning of Time String theory suggests that the big bang was not the origin of the universe but simply the outcome of a preexisting state
Atoms of Space and Time We perceive space and time to be continuous, but if the amazing theory of loop quantum gravity is correct, they actually come in discrete pieces
The Frontiers of Physics
Introduction Things get weird--spectacularly so--at the borderlands of physics. The rarefied realms described mathematically and sometimes glimpsed in experiments are all the more extraordinary for not being the mere products of someone's hyperactive imagination.

For instance, string theory's equations imply that the universe contains six extra dimensions, which are too tiny to have yet been detected. Some physicists also see innumerable theoretical universes in their equations. And although we perceive space and time as being continuous, quantum principles imply that, in fact, at the very smallest scales they actually come in pieces. The effects of this discrete structure could be revealed in experiments in the near future.

Intellectual enrichment aside, it might be tempting to think that none of what scientists are learning by probing the frontiers of physics truly matters in our everyday lives. Not so. As just one example, consider general relativity, which explains how gravity results from bends in the fabric of spacetime itself. To be accurate, commonplace GPS receivers--which calculate location using a constellation of orbiting satellites--must take the effects of general relativity into account.

The Dawn of Physics beyond the Standard Model The Standard Model of particle physics is at a pivotal moment in its history: it is both at the height of its success and on the verge of being surpassed
The Search for Relativity Violations To uncover evidence for an ultimate theory, scientists are looking for infractions of Einstein's once sacrosanct physical principal
Solving the Solar Neutrino Problem The Sudbury Neutrino Observatory has solved a 30-year-old mystery by showing that neutrinos from the sun change species en route to the earth
The Mysteries of Mass Physicists are hunting for an elusive particle that would reveal the presence of a new kind of field that permeates all of reality. Finding that Higgs field will give us a more complete understanding about how the universe works
The String Theory Landscape The theory of strings predicts that the universe might occupy one random "valley" out of a virtually infinite selection of valleys in a vast landscape of possibilities
The Future of String Theory: A Conversation with Brian Greene The physicist and best-selling author demystifies the ultimate theories of space and time, the nature of genius, multiple universes, and more
Atoms of Space and Time We perceive space and time to be continuous, but if the amazing theory of loop quantum gravity is correct, they actually come in discrete pieces
A Cosmic Conundrum A new incarnation of Einstein's cosmological constant may point the way beyond general relativity
Information in the Holographic Universe Theoretical results about black holes suggest that the universe could be like a gigantic hologram
That Mysterious Flow From the fixed past to the tangible present to the undecided future, it feels as though time flows inexorably on. But that is an illusion
Our Ever Changing Earth
Introduction It's so boring, the usual human's-eye view. Seasons come and go, but terra firma itself never varies. Even an earthquake or a mudslide seems like a random incident unconnected to any larger or more complex patterns.

But put on the lenses of a geologist and take another look. Reading the stories imprinted on the rocks and crystals gives scientists the ability to examine our world as it has evolved over millions, even billions, of years. From this vantage point, it is easy to see that Earth has been--and continues to be--a lively cauldron of change. Just as stop-action photography shows how buds burst into flower, geology gives us a picture of a living, changing planet.

The Evolution of Earth The evolution of this planet and its atmosphere gave rise to life, which shaped Earth's subsequent development. Our future lies in interpreting this geologic past and considering what changes--good and bad--may lie ahead
Earth before Pangaea The North American continent may be more nomadic than most of its inhabitants
The Mid-Cretaceous Superplume Episode Earth has an erratic "heartbeat" that can release vast amounts of heat from deep within the planet. The latest "pulse" occurred 120 million years ago
Probing the Geodynamo Scientists have wondered why the polarity of Earth's magnetic field occasionally reverses. Recent studies offer intriguing clues about how the next reversal may begin
The Core-Mantle Boundary This interactive zone may be the most dynamic part of the planet, directly affecting Earth's rotation and magnetic field
The Evolution of Continental Crust The high-standing continents owe their existence to Earth's long history of plate-tectonic activity
Panoramas of the Seafloor Modern sonar techniques map the continental margins of the U.S. and reveal the richly varied scenery usually hidden underwater
Sculpting Earth from Inside Out Powerful motions deep inside the planet do not merely shove fragments of the rocky shell horizontally around the globe--they also lift and lower entire continents
Earth's Mantle below the Oceans Samples collected from the ocean floor reveal how the mantle's convective forces shape Earth's surface, create its crust and perhaps even affect its rotation
How Erosion Builds Mountains An understanding of how tectonic, erosional and climatic forces interact to shape mountains permits clearer insights into Earth's history
Earthquake Conversations Contrary to prevailing wisdom, large earthquakes can trigger or inhibit one another in unexpected ways. This exciting discovery could dramatically improve scientists' ability to pinpoint future shocks
The Threat of Silent Earthquakes A lack of rumbling does not necessarily make an earthquake harmless. Some of the quiet types could presage devasting tsunamis or larger, ground-shaking shocks
New Light on Deep Earthquakes Until about 15 years ago, it was a mystery how deep earthquakes could occur. Recent results have now demonstrated mechanisms for such rock failures at great depths
Mysteries of the Ancient Ones
Introduction Lacking direct communiqués from ancient peoples, archaeologists turn to other clues--their structures, their artwork, their tools, even their very bones. Examining such relics, scientists attempt to fit the pieces into a comprehensive cultural picture. As fellow members of humanity, the ancient ones must have been very much like us in many ways. But the latest excavations are uncovering some surprising differences as well.

Consider the denizens of Çatalhöyük, in central Turkey, 9,000 years ago. Oddly, they walked atop their city and entered their houses from above. They had no sidewalks, no front doors. Yet they had a remarkably modern knack for sharing tasks between the sexes. In Egypt circa 1500 B.C.E., even stonecutters had the chance to learn to read and write in a community that greatly valued literacy. Not all the civilizations' tales end well, of course. In the face of local environmental decline, the prehistoric people of Malta developed a consuming obsession with death, which may have led to the culture's demise.

These civilizations, among the others featured in this special edition of Scientific American, demonstrate an impressive power to puzzle and intrigue us across the span of time. In the pages that follow, we invite you to contemplate our shared human heritage, in all its glorious--and inglorious--forms.--

Lost Ways of Life Letter from the Editor
The Iceman Reconsidered Where was the Iceman's home, and what was he doing at the high mountain pass where he died? Painstaking research--especially of plant remains found with the body--contradicts many of the initial specualations
The Death Cults of Prehistoric Malta New archaeological excavations reveal that as the ancient island societies suffered from environmental decline, they developed an extreme religious preoccupation with life and death
Uncovering the Keys to the Lost Indus Cities Recently excavated artifacts from Pakistan have inspired a reevaluation of one of the great early urban cultures--the enigmatic Indus Valley civilization
Women and Men at Çatalhöyük The largest known Neolithic settlement yields clues about the roles played by the two sexes in early agricultural societies
Rock Art in Southern Africa Paintings and engravings made by ancestors of the San peoples encode the history and culture of a society thousands of years old
Life and Death in Nabada Excavations in northern Syria reveal the metropolis of Nabada, founded 4,800 years ago. Its elaborate administration and culture rivaled those of the fabled cities of southern Mesopotamia
The Tapestry of Power in a Mesopotamian City Mashkan-shapir was for a brief time one of the most important cities in the world. Its remains challenge traditional notions of power distribution in early urban society
Daily Life in Ancient Egypt Workmen and their families lived some 3,000 years ago in the village now known as Deir el-Medina. Written records from the unusually well educated community offer fascinating descriptions of everyday activities
Great Zimbabwe For centuries, this ancient Shona city stood at the hub of a vast trade network. The site has also been at the center of a bitter debate about African history and heritage
Precious Metal Objects of the Middle Sicán A Peruvian culture older than the Incas made unprecedented use of gold and other metals. Studies of Sicán metalworking techniques offer hints about this mysterious society
Life in the Provinces of the Aztec Empire The lives of the Aztec common people were far richer and more complex than the official histories would have us believe
Reading the Bones of La Florida New approaches offer insight into the lives of Native Americans after the Europeans arrived
The Secret Lives of Stars
Introduction For pure theatrics and spectacle, Hollywood celebrities have nothing on the denizens of the heavens. Stars are born, live and die in fiery and fascinating ways--ways that we have only recently been able to study in greater detail, like so many swarming paparazzi, using the long-range lenses created by improved techniques and new, sharper observatories.
Exposé on the Stars Letter from the Editor
The First Stars in the Universe Exceptionally massive and bright, the earliest stars changed the course of cosmic history
Fountains of Youth: Early Days in the Life of a Star To make a star, gas and dust must fall inward. So why do astronomers see stuff streaming outward?
Companions to Young Stars The surprising finding that even the youngest stars commonly exist in sets of two or three has revised thinking about the birth of star systems
The Discovery of Brown Dwarfs Less massive than stars but more massive than planets, brown dwarfs were long assumed to be rare. New sky surveys, however, show that the objects may be as common as stars
The Stellar Dynamo Sunspot cycles--on other stars--are helping astronomers study the sun's variations and the ways they might affect Earth
The Fury of Solar Storms Shock waves from the sun can trigger severe turbulence in the space around Earth, endangering satellites and astronauts in orbit. A novel spacecraft is showing how space storms develop
When Stars Collide When two stars smash into each other, it can be a very pretty sight (as long as you're not too close by). These occurrences were once considered impossible, but they have turned out to be common in certain galactic neighborhoods
X-ray Binaries In these systems, ultradense neutron stars feed on their more sedate companions. Such stellar cannibalism produces brilliant outpourings of x-rays and drastically alters the evolution of both stars
Magnetars Some stars are magnetized so intensely that they emit huge bursts of magnetic energy and alter the very nature of the quantum vacuum
Supersoft X-ray Stars and Supernovae Several years ago astronomers came across a new type of star that spews out unusually low energy x-rays. These so-called supersoft sources are now thought to be white dwarf stars that cannibalize their stellar companions and then, in many cases, explode
Binary Neutron Stars These paired stellar remnants supply exquisite confirmations of general relativity. Their inevitable collapse produces what may be the strongest explosions in the universe
The Brightest Explosions in the Universe Every time a gamma-ray burst goes off, a black hole is born
The Science of Staying Young
Introduction Merely accruing additional years beyond the biblical span of three score and 10 would be unwelcome if they just prolonged suffering from illness and infirmity. No, we want to live better, more youthful days while were living longer. Diet, exercise and a lucky draw from the gene pool can take us only so far, however. That's where science comes in. In this special edition from Scientific American, you'll find firsthand reports from the researchers leading the efforts to understand the mechanisms of aging. They are teasing out ways to slow the biological clock as well as the degradation that time imposes on our bodies and minds. They are battling the diseases of age, including cancer and heart disease. Medicine will continue to advance, and, we expect, society and policymakers will have to learn to adapt to the challenges of longevity--both providing it and providing for it--that await us all.
The Oldest Old People in their late 90s or older are often healthier and more robust than those 20 years younger. Traditional views of aging may need rethinking
Making Methuselah Immortality may not be in the cards, but worms, flies and pigeons may be able to teach us a thing or two about living better longer
Longevity: The Ultimate Gender Gap An American man's average life span is more than five years shorter than a woman's. Differing hormone levels and lifestyle choices may help explain the disparity
Will Human Aging Be Postponed? In theory, it certainly can be. Yet no single elixir will do the trick. Antiaging therapies of the future will undoubtedly have to counter many destructive biochemical processes at once
A Radical Proposal There may be a way to prevent ourselves from rusting from the inside out
The Serious Search for an Antiaging Pill In government laboratories and elsewhere, scientists are seeking a drug able to prolong life and youthful vigor. Studies of caloric restriction are showing the way
Times of Our Lives Whether they're counting minutes or years, biological clocks keep our brains and bodies on time, perhaps even on schedule for death
Atherosclerosis: The New View It causes chest pain, heart attack and stroke, leading to more deaths every year than cancer. The long-held conception of how the disease develops turns out to be wrong
Untangling the Roots of Cancer Recent evidence challenges long-held theories of how cells turn malignant - and suggests new ways to stop tumors before they spread
Restoring Aging Bones The bone decay of osteoporosis can cripple, but an improved understanding of how the body builds and loses bone is leading to ever better prevention and treatment options
Spare Parts for Vital Organs Engineers are creating artificial replacements for failing hearts, kidneys, pancreases and livers
Preventing Good Brains from Going Bad The fight against two life-robbing diseases, Alzheimer's and Parkinson's, has just begun
Promised Land or Purgatory? Whether old age is worth living depends largely on mental health
No Truth to the Fountain of Youth Fifty-one scientists who study aging have issued a warning to the public: no antiaging remedy on the market today has been proved effective. Here's why they are speaking up
Dinosaurs and Other Monsters
Introduction From a purely self-interested standpoint, it's good that the dinosaurs and their ancient ilk are dead. Yet they live on in our imaginations and our intellectual pursuits, where they retain the power to puzzle, fascinate and startle us. How did they hunt (and what hunted them)? Were they orphans from birth, surviving on instinct and appetite alone, or did parents nurture them? Over millennia, how did their species evolve?

Studying the mineralized remains of prehistoric beasts from the comfortable distance of a few eons, scientists have learned a great deal about how these awesome creatures stalked and swam through the long-ago world

Rulers of the Jurassic Seas Fish-shaped reptiles called ichthyosaurs reigned over the oceans for as long as dinosaurs roamed the land, but only recently have paleontologists discovered why these creatures were so successful
The Mammals That Conquered the Seas New fossils and DNA analyses elucidate the remarkable evolutionary history of whales
Breathing Life into Tyrannosaurus rex By analyzing previously overlooked fossils and by taking a second look at some old finds, paleontologists are providing the first glimpse of the actual behavior of the tyrannosaurs
Madagascar's Mesozoic Secrets The world's fourth-largest island divulges fossils that could revolutionize scientific views on the origins of dinosaurs and mammals
Dinosaurs of the Antarctic Their excellent night vision and apparent warm blood raise a question: Could they have survived icehouse conditions at the end of the Cretaceous period?
Killer Kangaroos and Other Murderous Marsupials Australian mammals were not all as cute as koalas. Some were ferocious as they were bizarre
Fossils of the Flaming Cliffs Mongolia's Gobi Desert contains one of the richest assemblages of dinosaur remains ever found. Paleontologists are uncovering much of the region's history
Captured in Amber The exquisitely preserved tissues of insects in amber reveal unique secrets of evolution
Which Came First, the Feather or the Bird? A long-cherished view of how and why feathers evolved has now been overturned
The Terror Birds of South America These huge, swift creatures were the dominant carnivores of the continent for millions of years, until competitors drove them into extinction
The Evolution of Life on Earth The history of life is not necessarily progressive; it is certainly not predictable. The earth's creatures have evolved through a series of contigent and fortuitous events
New Light on the Solar System
Introduction The more we learn about our solar system, the more fascinating it becomes. The sun's atmosphere is hotter than its surface. Venus suffers from a greenhouse effect run amok. On Mars, geologic forces unlike those seen on Earth help to sculpt the landscape. Tiny moons stabilize the ethereal rings around the gas giants. Jupiter's satellite Europa has icy niches where life might evolve.

Though astronomers have begun to detect planetary systems around other stars, the uniqueness of ours is so far intact. Many planets in far-off systems seem to be freakishly large and moving in bizarre orbits that would devastate any alien Earths out there. One of the greatest mysteries of our solar system may be why it is so stable.

The Planets in Our Backyard Letter from the editor
The Paradox of the Sun's Hot Corona Like a boiling teakettle atop a cold stove, the sun's hot outer layers sit on the relatively cool surface. And now astronomers are figuring out why
Mercury: The Forgotten Planet Although one of Earth's nearest neighbors, this strange world remains, for the most part, unknown
Global Climate Change on Venus Venus's climate, like Earth's, has varied over time - the result of newly appreciated connections between geologic activity and atmospheric change
The Origins of Water on Earth Evidence is mounting that other planets hosted oceans at one time, but only Earth has maintained its watery endowment
The Unearthly Landscapes of Mars The Red Planet is no dead planet
The Small Planets Asteroids have become notorious as celestial menaces but are best appreciated in a positive light, as surreal worlds bearing testimony to the origin of the planets
The Galileo Mission to Jupiter and Its Moons Galileo spacecraft, beset by technical troubles, still conducted a comprehensive study of the Jovian system. Few predicted that the innards of these worlds would prove so varied
The Hidden Ocean of Europa Doodles and freckles, creamy plains and crypto-icebergs - the amazing surface of Jupiter's brightest icy moon hints at a global sea underneath
Bejeweled Worlds What an impoverished universe it would be if Saturn and the other giant planets lacked rings. Planetary scientists are finally working out how gravity has sculpted these elegant ornaments
Journey to the Farthest Planet Scientists are finally preparing to send a spacecraft to Pluto and the Kuiper belt, the last unexplored region of our planetary system
The Oort Cloud On the outskirts of the solar system swarms a vast cloud of comets, influenced almost as much by other stars as by our sun. The dynamics of this cloud may help explain such matters as mass extinctions on Earth
New Look at Human Evolution
Introduction Reading the cracked brown fragments of fossils and sequences of DNA, scientists have found clues that the story of human origins has more convolutions than previously thought. The account of our shared human heritage now includes more controversial plot twists and mysteries. Was the remarkable seven-million-year-old skull found in July 2002 in Chad really one of our first forebears, or a distant dead-end cousin with precociously evolved features? Did modern humans really originate in Africa alone, as is widely held, or in multiple locales? Were Neandertals the crude, brutish cavemen of comic strips or did they have a refined, artistic culture? And of course, why didn't our kind perish with the rest of the hominids? Were we luckier, more lingual or just more lethal than the rest?
An Ancestor to Call Our Own Controversial new fossils could bring scientists closer than ever to the origin of humanity
Early Hominid Fossils from Africa A new species of Australopithecus, the ancestor of Homo, pushes back the origins of bipedalism to some four million years ago
Once We Were Not Alone Today we take for granted that Homo sapiens is the only hominid on earth. Yet for at least four million years many hominid species shared the planet. What makes us different?
Who Were the Neandertals? Controversial evidence indicates that these hominids interbred with anatomically modern humans and sometimes behaved in surprisingly modern ways
Out of Africa Again...and Again? Africa is the birthplace of humanity. But how many human species evolved there? And when did they emigrate?
The Multiregional Evolution of Humans Both fossil and genetic evidence argues that ancient ancestors of various human groups lived where they are found today
The Recent African Genesis of Humans Genetic studies reveal that an African woman from less than 200,000 years ago was our common ancestor
Food for Thought Dietary change was a driving force in human evolution
Skin Deep Throughout the world, human skin color has evolved to be dark enough to prevent sunlight from destroying the nutrient folate but light enough to foster the production of vitamin D
The Evolution of Human Birth The difficulties of childbirth have probably challenged humans and their ancestors for millions of years - which means that the modern custom of seeking assistance during delivery may have similarly ancient roots
Once Were Cannibals Clear evidence of cannibalism in the human fossil record has been rare, but it is now becoming apparent that the practice is deeply rooted in our history
If Humans Were Built to Last We would look a lot different if evolution had designed the human body to function smoothly for a century or more
The Edge of Physics
Introduction Warp drive. Teleportation. Wormholes. A unifying "theory of everything"--maybe. In recent years scientists have been pushing the boundaries of physics, with fascinating results. Now in this special collector's edition, SCIENTIFIC AMERICAN provides a must-have compilation of updated feature articles that explore the current edge of physics.
A Unified Physics by 2050? Experiments at CERN and elsewhere should let us complete the Standard Model of particle physics, but a unified theory of all forces will probably require radically new ideas
The Theory Formerly Known as Strings The Theory of Everything is emerging as one in which not only strings but also membranes and black holes play a role
Black Holes and the Information Paradox What happens to the information in matter destroyed by a black hole? Searching for that answer, physicists are groping toward a quantum theory of gravity
Simple Rules for a Complex Quantum World An exciting new fundamental discipline of research combines information science and quantum mechanics
Quantum Teleportation The science-fiction dream of "beaming" objects from place to place is now a reality - at least for particles of light
Frozen Light Slowing a beam of light to a halt may pave the way for new optical communications technology, tabletop black holes and quantum computers
The Large Hadron Collider The Large Hadron Collider will be a particle accelerator of unprecedented energy and complexity, a global collaboration to uncover an exotic new layer of reality
The Asymmetry between Matter and Antimatter New accelerators are searching for violations in a fundamental symmetry of nature, throwing open a window to physics beyond the known
Detecting Massive Neutrinos A giant detector in the heart of Mount Ikenoyama in Japan has demonstrated that neutrinos metamorphose in flight, strongly suggesting that these ghostly particles have mass
Extreme Light Focusing light with the power of 1,000 Hoover Dams onto a point the size of a cell nucleus accelerates electrons to the speed of light in a femtosecond
Negative Energy, Wormholes and Warp Drive The construction of wormholes and warp drive would require a very unusual form of energy. But the same laws of physics that allow this "negative energy" also appear to limit its behavior
Plenty of Room, Indeed There is plenty of room for practical innovation at the nanoscale. But first, scientists have to understand the unique physics that governs matter there
The Once and Future Cosmos
Introduction The universe is a complicated place, to put it mildly, and scientists are working harder than ever to explain its mysteries. It is an exciting time: findings are pouring in, ideas are bubbling up, and research to test those ideas is simmering away. The latest special edition from Scientific American, The Once and Future Cosmos, brings together and updates firsthand reports from some of the world's most distinguished cosmologists. In this issue, expert authors discuss a range of topics--from the first stars and the big bang to the universe's unseen dimensions and Einstein's infamous cosmological constant. Other articles tackle such subjects as the fate of life in the universe and whether space might actually be finite.--The Editors
Making Sense of Modern Cosmology Confused by all those theories? Good
The First Stars in the Universe Exceptionally massive and bright, the earliest stars changed the course of cosmic history
The Life Cycle of Galaxies Astronomers are on the verge of explaining the enigmatic variety of galaxies
Surveying Spacetime with Supernovae Exploding stars seen across immense distances show that the cosmic expansion may be accelerating - a sign that an exotic new form of energy could be driving the universe apart
Cosmological Antigravity The long-derided cosmological constant - a contrivance of Albert Einstein's - may explain changes in the expansion rate of the universe
The Quintessential Universe The universe has recently been commandeered by an invisible energy field, which is causing its expansion to accelerate outward
The Fate of Life in the Universe Billions of years ago the universe was too hot for life to exist. Countless aeons from now, it will become so cold and empty that life, no matter how ingenious, will perish
Is Space Finite? Conventional wisdom says the universe is infinite. But it could be finite, merely giving the illusion of infinity
The Universe's Unseen Dimensions The visible universe could lie on a membrane floating within a higher-dimensional space
A Cosmic Cartographer The Microwave Anisotropy Probe will give cosmologists a much sharper picture of the early universe
Echoes from the Big Bang Scientists may soon glimpse the universe's beginnings by studying the subtle ripples made by gravitational waves
Exploring Our Universe and Others In this century cosmologists will unravel the mystery of our universe's birth - and perhaps prove the existence of other universes as well
Ripples in Spacetime Physicists have spent eight years and $365 million building a radically new kind of observatory to detect gravitational waves. But will it work? A trial run put it to the test
Plan B for the Cosmos If the new cosmology fails, what's the backup plan?
The Hidden Mind
Introduction Weighing just three pounds and encompassing some 100 billion neurons, the brain is the most complex organ in the human body. It and the spinal cord supervise all physical operations. And yet it has proved to be a most elusive organ, hiding the inner workings of the mind, which defines and creates our unique personalities, intellect and consciousness.

During the 1990s--dubbed the "decade of the brain" by presidential decree--scientists unraveled more about the brain's intricate, interconnected cascade of electrical impulses and chemical processes than would ever have seemed possible to many psychologists and neuroscientists just a few decades ago. These discoveries, which are proceeding at a rapid pace, could revolutionize treatments of various brain disorders.

The latest developments in these areas and more are addressed in this special edition from Scientific American. The Hidden Mind brings together and updates firsthand reports from some of the finest minds exploring the brain today. We welcome you to join us as we continue the age-old quest to understand our minds and ourselves. --the Editors

How the Brain Creates the Mind We have long wondered how the conscious mind comes to be. Greater understanding of brain function ought to lead to an eventual solution
The Problem of Consciousness It is now being explored through the visual system - requiring a close collaboration among psychologists, neuroscientists and theorists
Vision: A Window on Consciousness In their search for the mind, scientists are focusing on visual perception - how we interpret what we see
The Split Brain Revisited Groundbreaking work over four decades has led to ongoing insights about brain organization and consciousness
Sex Differences in the Brain Men and women display patterns of behavioral and cognitive differences that reflect varying hormonal influences on brain development
New Nerve Cells for the Adult Brain Contrary to dogma, the human brain does produce new nerve cells in adulthood. Can this lead to better treatments for neurological diseases?
Sign Language in the Brain How does the human brain process language? New studies of deaf signers hint at an answer
The Meaning of Dreams Dreams may be crucial in mammalian memory processing. Important information acquired while awake may be reprocessed during sleep
Emotion, Memory and the Brain The neural routes underlying the formation of memories about primitive emotional experiences, such as fear, have been traced
The Neurobiology of Fear Researchers are teasing apart the processes in the brain that give rise to various fears in monkeys. The results may lead to new ways to treat anxiety in humans
The Mind-Body Interaction in Disease The brain and the immune system continuously signal each other, often along the same pathways, which may explain how state of mind influences health
The Puzzle of Conscious Experience We are at last plumbing one of the most profound mysteries of existence. But knowledge of the brain alone may not get to the bottom of it

Compiled by Dave Lo, article summaries © Scientific American