For inspiration, you could hit the books: In Greek mythology, the goddess Athena wore an invisibility cap during the Trojan War. The same cap helped the half-god Perseus, who wore it to hide from Medusa, a monster who could turn someone to stone just by looking at them. In the books of J.R.R. Tolkein, Bilbo Baggins found a ring that could make him invisible; he passed it on to his nephew Frodo. And of course, there’s poor Harry Potter, who used his invisibility cloak to spy on classmates and teachers, hide from dragons or avoid certain spells cast on him by his enemies.

Now that you’ve got some ideas, it’s time for the hard part: building the cloak. To do that, you have to abandon science fiction and turn to real science. Two starting questions: How do you use visible materials to build something that’s supposed be invisible? How would you see it?

“If I were doing it, I’d built my invisibility device to have a remote control on/off switch,” says Steven Cummer, an engineer at Duke University in Durham, N.C. “This way I could have all of the pieces ‘off’ when it was being assembled. And if I lost track of it, I would have at least a chance of finding it by turning it off.”

Cummer has thought about this: In October 2006, Cummer was part of a team of scientists from Duke, including David R. Smith and David Schurig, who built the world’s first version of an invisibility cloak. They had been inspired by the work of a British physicist named John Pendry, who in May 2006 showed that an invisibility cloak was possible. And Pendry wasn’t the only one thinking about a disappearing act — at about the same time, a Scottish physicist named Ulf Leonhardt published a paper on building a cloaking device.

Less than half an inch tall and five inches across, this cloaking device was able to steer microwaves around it. The object to be hidden would be placed in the center.

Jack J. Mock, D. Smith Lab/Duke University

It wasn’t easy or perfect, Cummer says. “As often happens in science and research, it didn’t work very well the first time. It took several redesigns before we built something that worked pretty well.”

The device didn’t much resemble a cloak — at least, not one you would wear. It looked more like a set of circular fences nested inside each other, with a place inside for the object to be hidden. But up close, if you had a powerful magnifying glass, you would see tiny metal circles and rods that made intricate patterns all over these fences. These small details are one reason why the cloak works.

The device was small, about 5 inches across (roughly the diameter of a CD). Plus, that first cloak didn’t work like Harry Potter’s — the scientists didn’t actually see anything disappear.

Of course, they hadn’t expected to. That first version of the invisibility cloak didn’t shield objects from visible light. Instead, it hid things from a type of radiation called microwaves.

Moving the microwaves

An invisibility cloak has to deceive anything or anyone who might be watching. In order to understand how something can be invisible, it’s important to understand how we see.

Human beings see only objects that reflect light waves. These waves enter the eye and then are processed by the brain. But if an object doesn’t reflect light, then the waves don’t enter the eye, and the brain doesn’t process. The challenge of building an invisibility cloak is to build something that does not reflect or in any way interrupt waves of light.

Visible light has shorter wavelengths and higher frequencies than microwave radiation. So it will be harder to build a cloak that hides objects from visible light.

NASA

Light is a type of radiation, and all radiation travels in waves. Waves of radiation move through space somewhat as water waves do. And just as waves in the ocean have high points called crests and low points called troughs, radiation waves have crests and troughs. Unlike water waves, however, waves of radiation are made up of electric fields and magnetic fields that move together through space.

Scientists can learn a lot about a wave by measuring two things: its wavelength and its frequency. Wavelength is the distance from one crest to the next, and frequency is the number of waves that pass by a point in one second. Microwaves, for example, are more spread out than visible light — that means they have longer wavelengths and lower frequencies than visible light. (Microwave ovens, for example, heat food with microwaves that are about 13 centimeters, or about 5 inches, long.) In all kinds of radiation, frequency and wavelength are related — the higher the frequency, the shorter the wavelength. Waves of radiation differ by frequency and wavelength, and all the different types of waves together are called the “electromagnetic spectrum.”

At Duke, the engineers aimed microwave radiation at their device and took measurements. After the experiment, they looked at the data. According to their measurements, the device had shuffled the microwave radiation around the cylinder that is in the middle. Then, on the other side of the device, the waves had resumed their course — as though nothing had happened.

In other words, the waves of radiation moved around the device the way water waves move around a rock in the middle of a stream. Those tiny metal circles and rods were designed to change the directions of the electric and magnetic fields of the waves. By changing those fields in just the right way, the cloak could move the waves around itself.

Since that first successful test, in laboratories from North Carolina to California, Spain to Hong Kong, scientists have been racing to find ways to make invisibility a reality.

The Duke scientists made history with microwaves, but now scientists want to go further — and they are.

Last summer, for example, two independent teams of scientists announced they had created cloaks that worked for visible light. Unfortunately, those cloaks are tiny, so tiny that all they can hide are things so small that people already can’t see them. Plus, researchers have only redirected radiation that is at the far-red end of the electromagnetic spectrum — radiation with low frequency and long wavelengths.

Despite these problems, these breakthroughs are an important step forward in the science of disappearance and show that a cloak that can hide things from plain sight may not be far away.

Marvelous metamaterials

Invisibility cloaks would have remained impossible, forever locked in science fiction, had it not been for the development of metamaterials. In Greek, “meta” means beyond, and metamaterials can do things beyond what we see in the natural world — like shuffle light waves around an object, and then bring them back together. If scientists ever manage to build a full-fledged invisibility cloak, it will probably be made of metamaterials.

“We are creating materials that don’t exist in nature, and that have a physical phenomenon that doesn’t exist in nature,” says engineer Dentcho Genov. “That is the most exciting thing.” Genov designs and builds metamaterials — such as those used in cloaking — at Louisiana Tech University in Ruston, Louisiana.

An invisibility cloak will probably not be the first major accomplishment to come from the field of metamaterials. Other applications are just as exciting. In many labs, for example, scientists are working on building a hyperlens.

A lens is a device — usually made of glass — that can change the direction of light waves. Lenses are used in microscopes and cameras to focus light, thus allowing a researcher to see small things or a photographer to capture image of things that are far away.

A hyperlens, however, would be made of metamaterials. And since metamaterials can do things with light that ordinary materials can’t, the hyperlens would be a powerful tool. A hyperlens would allow researchers to see things at the smallest scale imaginable — as small as the wavelength of visible light.

Genov points out that the science of metamaterials is driven by the imagination: If someone can think of an idea for a new behavior for light, then the engineers can find a way to design a device using metamaterials. “We need people who can imagine,” he says.

Science of metamaterials just forming

The idea of invisibility has shown up in books for centuries, but the science of metamaterials is in its first chapter. Scientists are excited at the possibilities. Since 2006, many laboratories have been exploring other kinds of metamaterials that don’t involve just visible light. In fact, scientists are finding that almost any kind of wave may respond to metamaterials.

At the Polytechnic University of Valencia in Spain, José Sánchez-Dehesa is working with acoustics, or the science of sound. Just as an invisibility cloak shuffles waves of light, an “acoustic” cloak would shuffle waves of sound in a way that’s not found in nature. In an orchestra hall, for example, an acoustic cloak could redirect the sound waves — so someone sitting behind a column would hear the same concert as the rest of the audience, without distortion.

Sánchez-Dehesa , an engineer, recently showed that it’s possible to build such an acoustic cloak, though he doubts we’ll see one any time soon. “In principle, it is possible,” he says, but it might be impossible to make one, he adds.

Other scientists are looking into ways to use larger metamaterials as shields around islands or oil rigs as protection from tsunamis. A tsunami is a giant, destructive wave. The metamaterial would redirect the tsunami around the rig or island, and the wave would resume its journey on the other side without causing any harm.

One of the strangest new ideas for metamaterials came from a team that included Genov when he was a researcher at the University of California, Berkeley. There, he worked with Xiang Zhang and other engineers on the idea of “matter cloaking.” Just as an optical cloak could redirect light, a matter cloak would be able to redirect something solid — such as, say, a bullet. Genov says a matter cloak, were it possible to build, would be a perfect bulletproof vest. The bullet, as it approached the vest, would actually split into multiple pieces and move around the person — and then form again on the other side.

Genov says that the story of metamaterials and cloaking devices is just beginning, and that we’ll probably see a lot more strange, new devices in the very near future. Right now, scientists are working around the clock to build as many strange new devices as they can.

“They’re not perfect yet, but we’re in the beginning of the science,” says Genov. “We’re at the tip of the iceberg and the iceberg is very deep.”

The football-field–size machine, called a synchrotron, uses tubes, magnets, vacuum pumps, and other gadgetry to produce intensely powerful beams of light. The giant contraption looks like something out of a science fiction movie.

From above, the Australian synchrotron doesn’t look like much. Inside the football-field–size machine, tiny but powerful experiments are going on.

Australian Synchrotron Project

But it’s no fantasy. Real scientists are using these huge machines to look deeper than ever into the structure of atoms and cells. The work is giving them insights into our bodies and our world.

“Every kid knows about microscopes that let you see what the eye can’t see,” says Daniel Häusermann, an imaging and medical therapy scientist. He works with the Australian synchrotron, which began conducting experiments in April 2007.

“This is [like] the next level of microscope,” Häusermann says. “We always want to see … the unknown. This is what is fascinating.”

Fast particles

The Australian synchrotron is a type of machine called a particle accelerator. To understand how it works, you have to know some things about matter—the “stuff” that makes up everything in the universe.

All matter is made up of tiny particles called atoms. There are more than 100 types of atoms, including hydrogen, oxygen, and nitrogen. Just like the 26 letters of our alphabet combine to make up all the words in our language, atoms combine into molecules to make up everything we know. One atom of oxygen and two atoms of hydrogen, for example, form a molecule of water.

But atoms themselves are made up of even smaller particles. There are three types of such particles: protons, neutrons, and electrons.

And it is electrons that make synchrotrons tick. These particles have electric charges. When electrons move, they create electric currents.

Inside a synchrotron, big magnets, like the six shown above, help get electrons moving at nearly the speed of light.

Australian Synchrotron Project

A synchrotron uses giant magnets, radio waves, and something called an electron gun to push electrons until they move at a blistering 99.9987 percent of the speed of light. That’s almost 300,000 kilometers (186,000 miles) per second. Nothing we know of moves faster than light.

Once the electrons get moving in the synchrotron, they travel through a large, ring-shaped tube that measures 216 meters (709 feet) around. The electrons make 1.34 million laps around the ring in a single second. Moving at that rate, they could zoom around the world seven times in the same amount of time.

Follow the numbers to track the movement of electrons through a synchrotron. The electrons pick up speed as they zoom through the inner ring. Numbers 5 and 6 show where a powerful beam of light emerges at perpendicular angle from the central ring.

Australian Synchrotron Project

Electrons moving that quickly produce extremely bright light. Inside the synchrotron, magnets direct this light into beams, called beamlines, which come out of the machine in straight lines perpendicular to the central ring (see illustration above).

A technician examines the inner workings of the Australian synchrotron.

Australian Synchrotron Project

A synchrotron’s beamlines are between 30,000 and 30 million times as bright as the light that comes out of a laser pointer. Because synchrotrons create such strong, focused light, these machines can be used for a huge range of applications, from designing life-saving therapies to creating tastier chocolate.

“In the world of synchrotrons, you meet people who do everything,” Häusermann says, including chemists, doctors, and food researchers. “It’s more interesting than any world I’ve seen.”

Working with light

Light comes in a range of energies, called wavelengths. Some wavelengths of light we can see. Of those, we see different wavelengths in different colors. The color red, for example, has lower energy than the color violet. Other wavelengths, including high-energy X rays and low-energy infrared light, are invisible to human eyes.

Each beamline in a synchrotron is designed to emit just one type of light with a very specific amount of energy. The Australian synchrotron can produce light at wavelengths ranging from infrared to X rays. Each type of light can be used for very different purposes.

Scientists already use different types of light to do different things. Night-vision goggles, for example, use infrared light to reveal pockets of heat, allowing the wearer to “see” in the dark. And X-ray machines allow doctors to see through a patient’s skin and muscle all the way to the bone.

Because synchrotron beamlines are so powerful, they can be used for even more high-tech applications. Infrared beamlines, for example, can be used to study fragile archaeological remains and to examine processes inside living cells. Häusermann, for one, plans to work with a beamline that will produce superpowerful X rays for medical applications.

Researcher Daniel Häusermann plans to use the Australian synchrotron to see inside the human body in greater detail than ever before.

Emily Sohn

Now under construction, this X-ray beamline intended for medical purposes will travel 150 meters (492 feet) in a straight line away from the central ring through a tunnel into another building.

At the point where the beam emerges from the machine, it will measure just 1 cm (0.4 inch) across. The beam will get wider as it travels. By the time it gets to its destination, it will be 60 cm (24 inches) wide.

“We will have the widest [synchrotron X-ray] beam in the world,” Häusermann says.

He and colleagues plan on using the beamline to help cancer patients. The beam’s great width will allow the researchers to easily examine an entire body part, such as the chest. Though conventional X rays already allow researchers to see inside the body, the synchrotron’s powerful X-ray beams will allow doctors to see inside a single cell.

Better images will give all doctors a clearer window into the workings of the human body, Häusermann says, even those who don’t have the time or money to use synchrotron technology.

“The whole medical community learns from what is being done in the synchrotron,” he says.

The synchrotron can be used to treat diseases, as well as to diagnose them. For example, doctors also often use X rays to kill cancer cells. Radiation treatments are imprecise, however, and many healthy cells die in the process. That makes cancer patients feel sick. By using the highly focused synchrotron X-ray beam, scientists hope to destroy individual cancer cells without harming healthy tissues.

This illustration shows a high-powered beamline emerging from the synchrotron into an experimental booth.

Australian Synchrotron Project

So far, five beamlines are working at the Australian synchrotron. Four more are under development. Eventually, there may be as many as 30.

Solving mysteries

Medicine isn’t the only field benefiting from synchrotron technology. In 1998, a chocolate company in the United Kingdom used the UK synchrotron to study individual molecules during the production of chocolate.

The synchrotron’s X-ray beam revealed that the company was keeping the temperature too high for too long while processing the chocolate, says Stefanie Pearce, communications manager at the Australian synchrotron. The company changed its production methods. The result? A smoother, better-tasting chocolate.

SNK reporter Emily Sohn marvels at the complexity of the Australian synchrotron.

Hannah Hoag

By revealing molecule-size details such as these, synchrotrons have also helped scientists create more-absorbent baby diapers, better packaging for potato chips, and higher-performing jet engines.

Synchrotron techniques are also helpful in solving crimes. That’s because they can identify specks of sweat, poison, and counterfeit ink that are undetectable by conventional forensic techniques.

Researchers can even use synchrotrons to solve historical mysteries. Consider, for example, the mysterious death of Phar Lap, one of the greatest racehorses that ever lived.

In 1932, at the height of his career, Phar Lap was suddenly stricken with a high fever and severe pain. He died soon after, and an examination showed an inflamed stomach. Immediately, people began wondering whether the horse had been poisoned.

Firm proof did not come until 2006, when Australian researchers used a synchrotron’s X-ray beam to analyze a sample of Phar Lap’s hair. The test revealed traces of arsenic. The scientists concluded that it was almost certain the horse had been poisoned with a large dose of this toxic chemical.

The list of synchrotron applications goes on and on. And the work, Häusermann says, is endlessly fascinating.

“We’re just big kids,” he says, “Playing with expensive toys.”

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For many people in the United States, the Fourth of July means one thing: Fireworks. And they’re not alone.

Independence Day fireworks at Riverside Park in Yankton, Missouri.

National Park Service photo by Linda Gordon Rokosz

“Every country, it seems, has a fireworks day,” says John Conkling. He’s a chemist and fireworks researcher at Washington College in Chestertown, Md. “People universally seem to get a deep satisfaction from watching fireworks,” he says.

Viewer satisfaction demands serious science. All year long, researchers such as Conkling mix and burn chemicals in the lab to see what kinds of flames they can create. Now, with advances in technology and chemistry, holiday celebrations are more dazzling and colorful than ever.

People have been watching fireworks for more than 2,000 years. “There has been a really dramatic change in the appearance of fireworks,” Conkling says, “from merely being devices that go up into the air and explode to the dramatic color displays we have today.”

Gunpowder blasts

At its core, a firework contains a mixture of chemicals that burn well. These mixtures are produced in the form of gumball-sized pellets, which are held inside a cylindrical shell, or cartridge. Gunpowder at the bottom of the cartridge launches and ignites the firework. A special fuse delays the explosion until the cartridge is airborne.

Every type of firework is designed to burn for a certain amount of time in particular colors and patterns. The presence of different chemicals produces different colors.

Fireworks at Mount Rushmore National Monument in South Dakota.

National Park Service

Sodium compounds, for instance, produce a yellow flame when burned. Barium nitrate burns green, and magnesium and aluminum burn white.

If Conkling wants to make violet, he has to mix a red-producing chemical, such as strontium nitrate, with blue-producing copper salts. The more strontium nitrate and less copper that he uses, the redder the final shade will be.

“There’s really no color that you can’t make,” Conkling says.

Bursting suns

When Conkling develops fireworks, he starts with what he already knows about how particular chemicals burn. Then, he puts materials together in his lab and ignites them under a ventilated hood. He alters proportions through a process of trial and error to get the result that he wants.

Fireworks display on July 3, 2003, at the Cowpens National Battlefield in South Carolina.

National Park Service

Certain chemicals, combinations of chemicals, and packaging strategies produce special effects. Fireworks that burn slowly, for example, leave trails behind them and look like strings of colored spaghetti. Quick burners look like bursting suns.

Some ingredients produce streaks of light that dart around like grasshoppers trapped in a jar. If materials are pressed tightly in a tube, blowing them up makes loud whistling noises. The addition of a type of chemical known as a perchlorate makes a big, loud boom.

“The sky’s the limit, so to speak,” Conkling says. “Imagination is the only limiting factor.”

When lab tests are complete, companies make pellets of the new mixtures to try them outdoors before manufacturing them in large numbers.

Electronic control

One of the newest trends in fireworks, Conkling says, is the use of patterns. By arranging pellets in a flat layer inside the cartridge, researchers have figured out how to make fireworks that explode in the shape of hearts, Olympic rings, and other objects.

4th of July fireworks at Gloucester, Massachusetts.

Commander John Bortniak, NOAA Corps (ret.)

However, the shapes are clearly visible only from certain angles. “The biggest challenge is to get them oriented,” Conkling says.

The only solution at this point is to launch three or four of each shape at a time. “When they burst, one is usually quite apparent to people on the ground,” Conkling says. “People in other locations might see another one better.”

Fireworks experts have also moved into the computer age. Instead of lighting fireworks by hand, which is dangerous, major shows now rely on electronic devices and cables to control the timing of the launches.

Computer programs also allow choreographers to set off explosions that match music playing in the background. Such touches are always big crowd-pleasers.

Studying fire

The more you learn about fireworks, the more you might appreciate the Fourth of July and other celebrations with the eye of a scientist.

Fireworks at the National Mall, with a view across the Potomac River toward the Washington Monument and the Lincoln Memorial.

National Park Service

“I’m sure I view presentations quite a bit differently than many people,” Conkling says. “I try to analyze everything. I love when I see something that I haven’t seen before. Then, I try to figure out how they did that particular effect.”

Even just studying fire and explosions can be exciting, Conkling adds. It’s a great area to work in, he says. “I get a bang out of it.”

For safety’s sake, it’s best to avoid experimenting with any type of flame or explosive chemical unless you’re working alongside a trained professional. Lots of people end up in the emergency room every year with severe burns after launching their own explosives.

Instead, if you watch a fireworks show this year, try to focus on what you see and hear. After all, every bang, sparkle, burst, and boom is an amazing example of chemistry in action.

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