What is GPS?

It's a device used widely in cars, on smartphones and in fitness devices. But what exactly is GPS, and how is it able to pinpoint our exact location anywhere on Earth?

How does it work?

The Global Positioning System (GPS) is a constellation of up to32 satellites that orbit at a height of 26,600km above Earth. The satellites are owned by the US Department of Defense, but anyone can use the signals from those satellites, provided they have a receiver. For the receiver to work, it needs to be able to "see" four of the satellites. When you turn on your receiver, it may take a minute or so to locate these satellite signals, then to download data from the satellite before positioning can commence.

Fundamentally, two things need to happen for this to work effectively:

1) The GPS receiver measures the distance from itself to a satellite by measuring the time a signal takes to travel that distance at the speed of light.

2) When the satellite's position is known, the GPS receiver knows it must lie on a sphere that has the radius of this measured distance with the satellite at its centre. The receiver need only intersect three such spheres, as seen in the image below. This process, known as trilateration, is an effective means of determining absolute or relative locations. But there's a problem. Although the GPS satellites have veryexpensive atomic clocks on board – and therefore know what time their signals are transmitted – the GPS receiver has a very cheap clock. That means there is uncertainty about the "receive" time. So, instead of three satellites, the GPS receiver must receive four, so it can account for what's known as the receiver clock drift.

The great test tube in the sky

Space is one big chemistry set
MOST people think of the empty space between the stars as being, well, empty. But it is not. It is actually filled with gas. Admittedly, at an average density of 100-1,000 molecules per cubic centimetre (compared with 100 billion billion in air at sea level), it is a pretty thin gas. But space is big, so altogether there is quite a lot of it.

Most of it, about 92%, is hydrogen. A further 8% is helium, which is chemically inert. But a tiny fraction—less than one-tenth of a percent—consists of molecules with other elements, such as oxygen, carbon and nitrogen, in them. Though these other elements are a mere soupçon of the interstellar soup, they do give it real flavour.

Nanotechnology Used to Purify Urban Wastewater without Formation of Sludge

TEHRAN (FNA)- Iranian experts presented a new reactor in the Water and Environment Zone of Iran Nano 2012 which operates based on the performance of photocatalytic nanoparticles and can efficiently purify urban wastewater.

Among the advantages of the reactor, mention can be made of the fact that no sludge is produced during the purification process. 

Three processes photocatalysis, ultrasonic, and ozonation have been used in the reactor in order to optimize the performance of the purification of pollutants existing in urban wastewater. The device is controlled digitally through the installed switches. Wastewater, approximately 5 liters in volume, enters the device through a diaphragm pump. 

Then, nanoparticles are injected into the vessel through a vent installed in the upper part of the reactor. Ultrasonic device is turned on, and nanocatalyst particles are dispersed homogenously within the wastewater. 

The ultrasonic waves are both able to disperse nanoparticles and to decompose pollutants in the wastewater. Ozonation device is taken into the reactor through a hatch, and is dispersed in the wastewater by a diffuser device. 

Among the advantages of the implementation of this reactor in wastewater purification process, mention can be made of the lack of the formation of sludge during the process, low time of the process in comparison with the traditional methods, and the disinfection of the exit water through sonoluminescence process. 

Predator and prey, together forever Fossil shows spider in mid-strike

A hundred million years ago, an amber flow spoiled a spider’s day: it had waited, possibly for hours, to ambush a wasp in its web, and just as it decided to strike, spider, wasp and web were all trapped forever.

The Early Cretaceous fossil preserves – with stunning clarity – the juvenile spider about to make a meal of a parasitic wasp that was trapped in its web. As Oregon State University professor emeritus George Poinar Jr put it: "This was the wasp's worst nightmare, and it never ended. The wasp was watching the spider just as it was about to be attacked, when tree resin flowed over and captured both of them."

The findings, published in Historical Biology, represent the first time a spider attack has been found as a fossil. The spider is an orb weaver, Poinar said; relatives still exist today, although the kind in the amber is extinct. The wasp is a relative of species which today are parasites on both spiders and their eggs.

There are also fifteen unbroken strands of the spider’s web also preserved in the fossil, the researchers say.

Half life of DNA: 521 Years.

Few researchers have given credence to claims that samples of dinosaur DNA have survived to the present day, but no one knew just how long it would take for genetic material to fall apart. Now, a study of fossils found in New Zealand is laying the matter to rest — and putting paid to hopes of cloning a Tyrannosaurus rex.

After cell death, enzymes start to break down the bonds between the nucleotides that form the backbone of DNA, and micro-organisms speed the decay. In the long run, however, reactions with water are thought to be responsible for most bond degradation. Groundwater is almost ubiquitous, so DNA in buried bone samples should, in theory, degrade at a set rate.

Determining that rate has been difficult because it is rare to find large sets of DNA-containing fossils with which to make meaningful comparisons. To make matters worse, variable environmental conditions such as temperature, degree of microbial attack and oxygenation alter the speed of the decay process.

But palaeogeneticists led by Morten Allentoft at the University of Copenhagen and Michael Bunce at Murdoch University in Perth, Australia, examined 158 DNA-containing leg bones belonging to three species of extinct giant birds called moa. The bones, which were between 600 and 8,000 years old, had been recovered from three sites within 5 kilometres of each other, with nearly identical preservation conditions including a temperature of 13.1 ºC. The findings are published today in Proceedings of the Royal Society B1.

Diminishing returns

By comparing the specimens' ages and degrees of DNA degradation, the researchers calculated that DNA has a half-life of 521 years. That means that after 521 years, half of the bonds between nucleotides in the backbone of a sample would have broken; after another 521 years half of the remaining bonds would have gone; and so on.

Related stories

The team predicts that even in a bone at an ideal preservation temperature of −5 ºC, effectively every bond would be destroyed after a maximum of 6.8 million years. The DNA would cease to be readable much earlier — perhaps after roughly 1.5 million years, when the remaining strands would be too short to give meaningful information.

“This confirms the widely held suspicion that claims of DNA from dinosaurs and ancient insects trapped in amber are incorrect,” says Simon Ho, a computational evolutionary biologist at the University of Sydney in Australia. However, although 6.8 million years is nowhere near the age of a dinosaur bone — which would be at least 65 million years old — “We might be able to break the record for the oldest authentic DNA sequence, which currently stands at about half a million years,” says Ho.

The calculations in the latest study were quite straightforward, but many questions remain.

“I am very interested to see if these findings can be reproduced in very different environments such as permafrost and caves,” says Michael Knapp, a palaeogeneticist at the University of Otago in Dunedin, New Zealand.

Moreover, the researchers found that age differences accounted for only 38.6% of the variation in DNA degradation between moa-bone samples. “Other factors that impact on DNA preservation are clearly at work,” says Bunce. “Storage following excavation, soil chemistry and even the time of year when the animal died are all likely contributing factors that will need looking into.”

What came first? Jaws or teeth?

A set of jaws can invoke visions of deadly toothy sharks, and now scientists find the earliest fish with chops — the ancestors of all jawed creatures with backbones — were also armed with teeth, researchers say.

The evolution of teeth and jaws in vertebrates — animals with backbones —about 420 million years ago is considered to be a key factor behind their success, making everything from a T. rex's razor-sharp teeth to a dwarf mammoth's grinding molars possible. However, whether jaws or teeth came first remains uncertain.

"It has long been thought that the first jawed vertebrates were gummy — [they had] jaws without teeth, capturing prey by suction-feeding," researcher Philip Donoghue, a paleontologist at the University of Bristol in England, told LiveScience.

To investigate this mystery, Donoghue and his colleagues analyzed 370-million-year-old fossils of a diverse and extinct group of armored fish known as placoderms, the first-known jawed vertebrates. These marine specimens were collected in Australia by researchers at the Natural History Museum London and from the Western Australia Museum.

The researchers analyzed specimens from an extinct placoderm, Compagopiscis, using high-energy X-rays from a kind of particle accelerator known as a synchrotron at the Swiss Light Source at the Paul Scherrer Institute in Switzerland.

"The fossils are very rare and so no museum would ever allow anyone to cut them up to study structure," Donoghue said.

Regular CT scanning would not reveal the internal structure of these fossils at a resolution fine enough to look for signs of teeth. "It is only with synchrotron tomography that we can obtain the high resolution we need using a non-destructive method," Donoghue said. This technique involves speeding charged particles through magnetic fields; the resulting release of high-energy light can penetrate opaque materials like bones to produce high-resolution 3D images.

"We were able to visualize every tissue, cell and growth line within the bony jaws, allowing us to study the development of the jaws," researcher Martin Rücklin at the University of Bristol said in a statement.

The placoderm teeth had components seen in modern teeth, such as dentin, the hard, dense bony tissue forming the bulk of the tooth beneath the enamel, and a pulp cavity, which creates dentin.

"We show that the juveniles had teeth for processing and capturing prey before they were worn away in the adults," Donoghue said.

Synthetic magnetic field to control photons!

Magnetically speaking, photons are the mavericks of the engineering world.Lacking electrical charge, they are free to run even in the most intense magnetic fields. But all that may soon change. In a paper published in Nature Photonics, an interdisciplinary team of Stanford physicists and engineers reports that they have created a device that tames the flow of photons with synthetic magnetism.

The process breaks a key law of physics known as the time-reversal symmetry of light and could yield an entirely new class of devices that use light instead of electricity for applications ranging from scientific devices such as accelerators and microscopes to speedier on-chip communications.

"This is a fundamentally new way to manipulate light flow. It presents a richness of photon control not seen before," said Shanhui Fan, a professor of electrical engineering at Stanford and senior author of the study.

A departure

The ability to use magnetic fields to redirect electrons is a founding principle of electronics, but a corollary for photons has not previously existed.

When an electron approaches a magnetic field, it meets resistance and opts to follow the path of least effort, traveling in circular motion around the field. Similarly, this new device sends photons in a circular motion around the synthetic magnetic field.

How did they do it?

The Stanford solution capitalizes on recent research into photonic crystals – materials that can confine and release photons. To fashion their device, the team members created a grid of tiny cavities etched in silicon, forming the photonic crystal. By precisely applying electric current to the grid they can control – or "harmonically tune," as the researchers say – the photonic crystal to synthesize magnetism and exert virtual force upon photons. The researchers refer to the synthetic magnetism as an effective magnetic field.

The researchers reported that they were able to alter the radius of a photon's trajectory by varying the electrical current applied to the photonic crystal and by manipulating the speed of the photons as they enter the system. Providing a great degree of precision control over the photons' path, this dual mechanism allows the researchers to steer the light wherever they like.

Broken laws

In fashioning the device, the team has broken what is known in physics as the time-reversal symmetry of light. Breaking time-reversal symmetry in essence introduces a charge on the photons that reacts to the effective magnetic field the way an electron would to a real magnetic field.

For engineers, it means that a photon traveling forward will have different properties than when it is traveling backward, the researchers said, and this yields promising technical possibilities. "The breaking of time-reversal symmetry is crucial as it opens up novel ways to control light. We can, for instance, completely prevent light from traveling backward to eliminate reflection," said Fan.

The new device, therefore, solves at least one major drawback of current photonic systems that use fiber optic cables. Photons tend to reverse course in such systems, causing a form of reflective noise known as backscatter.

"Despite their smooth appearance, glass fibers are, photonically speaking, quite rough. This causes a certain amount of backscatter, which degrades performance," said Kejie Fang, a doctoral candidate in physics at Stanford and the first author of the study.

In essence, once a photon enters the new device it cannot go back. This quality, the researchers believe, will be key to future applications of the technology, as it eliminates disorders such as signal loss common to fiber optics and other light-control mechanisms.

"Our system is a clear direction toward demonstrating on-chip applications of a new type of light-based communication device that solves a number of existing challenges," said Zongfu Yu, a postdoctoral researcher in Fan's lab and co-author of the paper. "We're excited to see where it leads."

A photo of artery taken by electron microscope.

Why you should brush your teeth: microscopic picture of a toothbrush bristle

What you are looking at is a coloured scanning electron micrograph (SEM) of a bristle from a used toothbrush, covered in dental plaque. Dental plaque is formed by colonizing bacteria trying to attach themselves to the tooth’s smooth surface. 

Parasitic Nematode Emerges From Spider Corpse

It's an example of a mermithid worm... which is a nematode, a worm which is a endoparasite which survives in arthropods like spiders. They work by slowly eating the spider up from the inside...consuming fluids, digestive glands, gonads. As this goes on, the spider becomes progressively dehabilitated but stays alive.

Mermithid worms can also be found in scorpions and crustaceans. Eventually, if they were left alone they would burst out of the arthropod's body like in the movie "Alien." The spider in this video died because it was sprayed, which is why the mermithid has emerged early. 

Speed of expansion of Universe measured more accurately

The universe is expanding – fast. Researchers had a pretty good idea how fast, but now, they measured in even greater detail: it is expanding at a rate of 74.3 plus or minus 2.1 kilometers (46.2 plus or minus 1.3 miles) per second per megaparsec (a megaparsec being about 3 million light-years). Hard to wrap your head around it?

The Hubble constant and the Doppler effect

The fact that the Universe is expanding faster and faster came as quite a shock to most of the scientific world in the 1990s, earning the 2011 Nobel prize. I mean, you’d expect it to be slowing down, since there shouldn’t be any force to provide the acceleration, right? Well, that’s not how it works. The acceleration of objects moving away from each other in an expanding universe is not the sort of acceleration which can be associated with a force as in Newton’s Second Law, which bounds together force, mass and acceleration.

This is where it gets a little tricky, but only at a first glance; the thing is, when you look at something which is moving relative to you, the light’s wave frequency changes. This frequency change is called the Doppler effect, or the Doppler shift, and it can be observed and calculated. The thing is, we notice this effect when analyzing any object in the deep space, and it seems that all objects in the Universe are drifting apart from each other, at a speed proportional with distance. So the further you are from something, the more you will move away from it – this is the Universe expanding.

The first one who described this was, contrary to popular belief, not Hubble – it was Georges Lemaître in a 1927 article. Hubble just refined his calculations and proposed a better rate of expansion, now called the Hubble constant. So, since the Hubble constant is associated with the Universe’s speed of expansion, calculate the Hubble constant and you also get the rate of expansion. Not so complicated now, is it?

Faster and faster

So how do you measure it? If you were a cosmic god of some sort, you could just take your cosmic god ruler, measure the distance between two points, wait a while, and then measure it again. Of course, since we’ve yet to find one of those, we have to employ different methods. Instead, we use an effect associated with this move – cosmic redshift. Cosmic redshift is what happens when light seen coming from an object that is moving away is proportionally increased in wavelength, and it is attributable to the Doppler effect. Using it, we can calculate, now with an uncertainty of just 3 percent, the rate at which the Universe is expanding – now we’re getting somewhere.

So what the first paragraph means is that two things at a distance of a mega parsec (roughly 3 million light years) will depart at a speed of about 74 kilometers per second, due to the Universal expansion. The 3 percent uncertainty is absolutely spectacular, considering how the second best measurement had an uncertainty 3 times larger.

“Just over a decade ago, using the words ‘precision’ and ‘cosmology’ in the same sentence was not possible, and the size and age of the universe was not known to better than a factor of two,” Wendy Freedman of the Observatories of the Carnegie Institution for Science in Pasadena, Calif., said in a statement. “Now we are talking about accuracies of a few percent. It is quite extraordinary.”

Faster, but… why?

If you’ve paid attention, you’ve probably noticed I avoided tackling an aspect: just why is the Universe expanding faster? Well, scientists have called whatever is making the Universe spread apart dark energy; but they don’t really know what dark energy is – it’s just a hypothetical form of energy that permeates all of space and accelerates universal expansion.This dark energy must be pretty strong stuff, since it fights against gravity trying to bind all things together and still manages to push things further.

By combining the new value of the Hubble Constant with observations of the universe by NASA’s Wilkinson Microwave Anisotropy Probe (WMAP), astrophysicists managed to make a good estimate of just how powerful dark energy really is.

“This is a huge puzzle,” Freedman said. “It’s exciting that we were able to use Spitzer to tackle fundamental problems in cosmology: the precise rate at which the universe is expanding at the current time, as well as measuring the amount of dark energy in the universe from another angle.”

Bizarre- The turtle that urinates through its mouth

Everyone knows the feeling of desperately needing to go to the loo. Bouncing from one foot to the other, you hare around in search of an appropriate facility, praying all the while that it won't be occupied.

When the Chinese soft-shelled turtle needs to urinate, its approach is a little different. It goes in search of a puddle, and dunks its head under the surface.

That's because the Chinese soft-shelled turtle is unique in the animal kingdom: it urinates through its mouth.

Chinese soft-shelled turtles are most commonly encountered as food in upscale restaurants. They're widely farmed in several Southeast Asian countries. Even as embryos, they are remarkable: a turtle embryo can move to the warmest spot in its egg when it has yet to develop limbs.

In the wild, they live in swamps and marshes where the water is often brackish: salty, but not as salty as seawater. They spend plenty of time out of water, especially in summer, though they often stick their heads into puddles.

Fingers in mouths

The linings of their mouths are covered with tiny, finger-shaped protrusions, discovered in the late 19th century. It turned out that they allow the turtles to breathe underwater: they increase the surface area of the mouth over which oxygen and carbon dioxide can be exchanged. The turtles can also take in other chemicals, such as sodium, through the protrusions.

But that's only part of the story, according to Alex Yuen Kwong Ip of the National University of Singapore. He thinks the turtles only started breathing underwater to make it easier to urinate through their mouths.

Working with Shit Fun Chew of Nanyang Technological University in Singapore, Ip kept four turtles in tanks of water for six days. Each turtle had a tube attached to its cloaca, where urine would normally exit the body. Ip sampled the tank water regularly, and collected any urine passed through the cloaca. Just 6 per cent of the turtle's urea came out of the cloaca. The rest turned up in the tank water.

Ip also tried restraining the turtles on land. When he placed a bucket of water in front of them, the turtles plunged their heads in for between 20 and 100 minutes. They held the water in their mouths for a while, then spat it out – at which point the urea concentration in the water increased.

Urea transporter*

Proteins in the turtle's mouth lining actively transport urea out of its bloodstream. Ip managed to identify one such transporter, and found that it was only present in the mouth lining, not in the kidney.

"I know of no other animals that can excrete urea through the mouth," says Ip. Most fish excrete through their gills, and some amphibians and lungfish may excrete through their skin, but the Chinese soft-shelled turtle's oral habit is almost certainly a one-off. Without the tiny protrusions in the animal's mouth, this could never work efficiently.

Ip thinks oral urination helped the turtles colonise brackish waters. To excrete urea through their cloaca via their kidneys, the turtles would need to drink a lot of water to flush it through. That would mean taking in a lot of salt, which would be difficult to get rid of. Rather than drinking the brackish water, the turtles' habits allow them to simply rinse their mouths with it.

As yet there is no record of the turtles washing their mouths out with soap and water. 

Reports put new spin on story of moon's creation

Scientists may never know exactly how the moon and Earth were formed some 4.5 billion years ago, but this week their understanding of the cataclysmic event made a significant leap forward.

In a slew of studies published Wednesday, planetary scientists provided new evidence supporting the long-standing — but imperfect — theory that the Earth and moon formed after the proto-Earth collided with another huge planetary body, sometimes referred to as Theia.


Some of that evidence comes from super-precise measurements of the zinc in lunar rock samples collected by Apollo astronauts. These findings, reported in the journal Nature, support the idea that the moon's birth had to have resulted from "a big event with lots of energy," strong enough to vaporize rock,  said study leader Frederic Moynier, a geochemist at Washington University.

Separately, two studies published in the journal Science detailed two scenarios of what such a powerful crash might plausibly have looked like.

Both collision-simulation papers may solve an intractable problem with the classic story scientists tell about the moon's birth. The story goes something like this: Two planets, one Earth-sized and one Mars-sized, slammed together. The smaller body, Theia, was obliterated completely, its materials flung asunder to form a disk around the Earth that before long coalesced to form the moon.

The theory explains the distance between the two bodies, their relative sizes and other physical properties. But in the last decade or so, a problem arose: The chemistry didn't match up with the physics.

"What's happening now is an attempt to salvage the theory," said Erik Asphaug, a planetary scientist at UC Santa Cruz who was not involved in the new research.

According to computer simulations of the theorized collision, the moon should have been composed mainly of materials from Theia. Instead, analysis showed that rock samples from the moon and Earth appeared to contain the same amounts of the same types of oxygen, titanium, silicon and other elements.

The similarity of these distinct chemical isotopes was taken as a sign that the Earth and moon were actually made of the same stuff — and meant that planetary scientists would need to rethink the details of how the giant impact happened, said Harvard University researcher Matija Cuk, a coauthor of one of the new simulations.

The main problem the computer modelers faced was that any collisions resulting in an Earth and a moon with shared geochemistry required the ancient Earth to be spinning too fast to allow for the 24-hour rotation that exists today.

Cuk and his Harvard colleague Sarah Stewart solved the conundrum by suggesting that a fast-spinning proto-Earth could have slowed during a period when the moon and the sun aligned in such a way that gravity warped Earth's orbit, putting the brakes on its rotation.

Plugging the appropriate conditions into their computer simulation, they found that a small body about half the size of Mars striking the early Earth nearly head-on would completely obliterate both bodies, with all the material mixing together.


"Everything is molten," Cuk said.

Most of the heavy iron from both planetary cores would combine and coalesce to form Earth's core. The blended lighter rock from both bodies would form the outer layers of the Earth as well as the moon.

Robin Canup, a planetary scientist at the Southwest Research Institute in Boulder, Colo., used Cuk's and Stewart's idea about how the Earth's rotation might have slowed and developed another scenario for the moon's creation. Also writing in Science, she showed that two similarly sized bodies, each about half the mass of the modern Earth, could have collided at a relatively slow speed and merged, their contents creating a pool of material that later split apart into Earth and moon.

By figuring out how Earth's spin might have slowed, Canup said, scientists have "greatly broadened the class of impacts that might be viable."

Caltech planetary scientist David Stevenson, who was not involved with the research, said that the new models "are a stepping stone toward a more satisfying story" but that "we're only part of the way."

David Paige, a moon expert at UCLA who was also not part of either modeling study, said it might not be possible to know exactly what happened.

"So much of what existed prior to the impact has been obliterated," he said. "It's a whodunit mystery with very few clues lying around."

He said, however, that isotopic research might offer part of the solution.

In the report published in Nature, Moynier and his colleagues used sophisticated mass spectrometry to show that the blend of different zinc isotopes on the moon is not the same as the blend on Earth. Lighter versions of the metal were slightly depleted on the moon, suggesting that the lighter zinc must have evaporated during some kind of impact, the team reported.

That doesn't do much to determine whether either collision scenario is correct. It may point a way forward for the planetary scientists who'll try to figure it out, however, Paige noted.

"It's through more measurements like this zinc one that we're able to better sort it out," he said.

For his part, Moynier said he planned to examine rubidium isotopes in lunar rocks next.

NASA Radar Images Asteroid 2007 PA8

Scientists working with NASA's 230-foot-wide (70-meter) Deep Space Network antenna at Goldstone, Calif., have obtained several radar images depicting near-Earth asteroid 2007 PA8. The images were generated from data collected at Goldstone on Oct. 28, 29 and 30, 2012. The asteroid's distance from Earth on Oct. 28 was 6.5 million miles (10 million kilometers). The asteroid's distance to Earth was 5.6 million miles (9 million kilometers) on Oct. 30. The perspective in the images is analogous to seeing the asteroid from above its north pole. Each of the three images is shown at the same scale. 

The radar images of asteroid 2007 PA8 indicate that it is an elongated, irregularly shaped object approximately one mile (1.6 kilometers) wide, with ridges and perhaps craters. The data also indicate that 2007 PA8 rotates very slowly, roughly once every three to four days. 

JPL scientists chose to image asteroid 2007 PA8 due to its size and relative proximity to Earth at the point of closest approach. On Nov. 5 at 8:42 a.m. PST (11:42 a.m. EST /16:42 UTC), the space rock was about four million miles (6.5 million kilometers) from Earth, or 17 times the distance between Earth and the moon. The trajectory of asteroid 2007 PA8 is well understood. This flyby was the closest Earth approach by this asteroid for at least the next 200 years. NASA detects, tracks and characterizes asteroids and comets passing close to Earth using both ground- and space-based telescopes. The Near-Earth Object Observations Program, commonly called "Spaceguard," discovers these objects, characterizes a subset of them, and plots their orbits to determine if any could be potentially hazardous to our planet. 

JPL manages the Near-Earth Object Program Office for NASA's Science Mission Directorate in Washington. JPL is a division of the California Institute of Technology in Pasadena.

Hiding in Plain Sight

Imagine yourself at a magic show. The magician brings out a tiger and coaxes it into a large, colorful box on the stage. He closes the lid, says a few mysterious words and then — poof — opens the side panel, revealing the inside of the box to be empty. The tiger is gone. Cue applause.

The tiger doesn't really vanish. So what happens?

The answer has much to do with the way our sense of sight works. As we look around a room, our eyes detect the light that bounces off nearby people or objects, and our brains interpret the images formed from the patterns of light received. We can even figure out what material something is made of based on the way it reflects and transmits light: metal is opaque and typically very reflective; plastic, which is more dull and often translucent, absorbs some of the light and reflects the rest in all directions. Our brains, then, turn these signals from reflections into breathtakingly complex pictures of the world around us. And it all happens faster than the blink of an eye. Indeed, after every blink of an eye.

Such lightning-fast cognitions are possible partly because the brain makes certain automatic assumptions: it figures that light has traveled in a straight line from the object to our eyes. Remarkably, in that built-in assumption is the recipe for a bit of magic that humans (and mythical humans) have sought, from the time of Plato to the age of Harry Potter:invisibility.

The trick involves the ability to bend and distort light as it travels through space — in other words, to make it do what the brain assumes it won’t. In some ways, it’s the same sleight of hand that the magician uses with the tiger. He uses a mirror angled in such a way that when we think we’re looking into an empty box, we’re actually seeing the reflection from the bottom of the box and assuming it’s the back. Since we don’t expect that the light reaching our eyes has swerved, making a 90-degree turn along the way, our eyes “tell” us the tiger has vanished. (In reality, he’s hiding comfortably in the box.)

Now we’ve found a way to one-up this neat trick with science: changing the trajectory of light without using mirrors. We do it with the science of materials — designing a “cloak” that can make light curve around an object, and then emerge just as if it had passed in a straight line through space. (Think of it like water flowing past a rock in a stream.)

The phenomenon is indeed supernatural. That’s because nature doesn’t appear to offer any materials that can accomplish this feat. The reason is that light has both electric and magnetic components — and to make it swerve around an object, one has to redirect both of these very different components and have them sync up immediately after the detour. That’s impossible to do with metals, fabrics or any other traditional materials.

But research findings over the past decade have shown us how to develop artificially structured “metamaterials” — in which tiny electrical circuits serve as the building blocks in much the same way that atoms and molecules provide the structure of natural substances. By changing the geometry and other parameters of those circuits, we can give these materials properties beyond what nature offers, letting us simultaneously manipulate both the electric and magnetic aspects of light in striking harmony.

This year, with one such metamaterial, we built the world’s first invisibility cloak capable of managing both components of light.

There is a catch, admittedly. These cloak works only on microwaves, not on visible light. And humans don’t “see” microwaves in the first place, making the idea of invisibility seem, well, a little extraneous.

Still, even if we mortals don’t see them, many essential devices do. Nearly every time you walk through security at an airport, your body is scanned with microwaves. Also, your cellphone, iPad and other devices make a similar kind of virtual eye contact with one another. So, even in the microwave realm, cloaking can potentially be used to remove obstacles from the paths of direct microwave communications (or hide things we don’t want detected).

More important, microwaves are part of the same electromagnetic spectrum as visible light. In principle, if cloaks can be made to work at microwave frequencies, they might one day be made to work at visible wavelengths.

This will be far more difficult: the wavelengths of visible light are more than 10,000 times smaller than those of microwaves, meaning that the corresponding metamaterials would have to be equally reduced in size.

What excites scientists and Harry Potter fans alike, though, is that our microwave cloak proves there’s no theoretical limitation that would prevent someone from building a visible-light cloak.

There are some tricky technological barriers to work out. But in this case, at least, not seeing is believing.