A Different Kind of Secret Code

Researchers have invented a new form of secret messaging using bacteria that make glowing proteins only under certain conditions. In addition to being useful to spies, the new technique could also allow companies to encode secret identifiers into crops, seeds, or other living commodities. 

The new glowing bacteria actually did grow out of a bit of cloak-and-dagger thinking. Several years ago, the Defense Advanced Research Projects Agency asked researchers to submit ideas for ways to encode secret messages without the need for electronics. At the time David Walt, a chemist at Tufts University in Medford, Massachusetts, teamed up with his former adviser George Whitesides, a chemist at Harvard University. Together, they came up with a way to add a variety of metal salts to a fuse that, when lit, would give off a sequence of pulses of infrared light that encoded a message. That got them thinking about other ways to accomplish the same thing. And so last year they decided to try something else, using bacteria to encode their secrets. 

The new scheme replaces the fuse with seven colonies of Escherichia coli bacteria, each given a gene for a different fluorescent protein. When, and only when, these genes are turned on do the bacteria make these proteins and light up. The colors, including yellow, green, and red, vary based on which gene is expressed. All are clearly visibly different to the naked eye. With their colorful bacterial colonies in hand, the researchers then created a code using pairs of different colored bacteria. Having seven colors gave them 49 combinations, which they used to encode the 26 different letters and 23 alphanumeric symbols such as "@" and "$." They wrote a message by simply blotting pairs of colored bacteria in rows. To "print" the message, the researchers transferred the bacteria onto a plate containing agar, a bacterial growth medium, into which they pressed a sheet of nitrocellulose "paper" that immobilizes the bacteria. 

At this point, the bacteria on the nitrocellulose paper remain invisible. But the message receiver can turn on the key genes and make the colors light up by pressing the nitrocellulose paper into an agar plate containing a chemical trigger that activates expression of the fluorescent proteins. (The proteins chosen to light up are ones the bacteria don't normally use, so unless the researchers activate them, they stay quiescent.) As long as the receiver knows which colors correspond to which characters, the message is revealed. But Walt and his colleagues added one more safeguard as well. Into some bacteria they inserted genes for resistance to particular antibiotics; the idea is that only the antibiotic-resistant bacteria are carrying the real message. If the message fell into the wrong hands, the receiver would see a mix of colors once the genes were activated and be unable to read it. But if the decoder added the right antibiotic, nonresistant bacteria and their colors die away, and the message becomes clear. The first example, reported in today's issue of the Proceedings of the National Academy of Sciences reads "this is a bioencoded message from the walt lab @ tufts university 2010." 

"It's a really cool idea," says Kenneth Suslick, a chemist at the University of Illinois, Urbana-Champaign. So cool in fact that much the same idea was suggested in Spiral, a science-fiction thriller published earlier this year by Cornell University physicist Paul McEuen. In the book, Liam Connor, an aging fungal biologist with enemies, encodes clues to solving a decades-old mystery by inserting genes for fluorescent proteins in the DNA of various fungi. Walt says he hadn't heard of the book, though as a science-fiction fan he's eager to read it. Now with the help of his glowing bacteria, he can write a few mysteries of his own.

Two weeks before his death, Stephen Hawking predicted 'the end of the universe'

• The world-famous physicist, who died last Wednesday aged 76, was a co-author to a mathematical paper in which he sought to prove the so-called "multiverse" theory, according to a report by U.K. newspaper The Sunday Times.
• Hawking's final work — titled "A Smooth Exit From Eternal Inflation" — is being reviewed by a leading scientific journal.
• In it, he predicted how our universe would eventually fade to darkness as the stars run out of energy.

Stephen Hawking completed a theory outlining his prediction for the end of the world just two weeks before his death, it has emerged.

The world-famous physicist, who died last Wednesday aged 76, was a co-author to a mathematical paper in which he sought to prove the so-called "multiverse" theory, according to a report by U.K. newspaper The Sunday Times. This theory imagines the existence of many separate universes other than our own.

Hawking's final work — titled "A Smooth Exit From Eternal Inflation" — is being reviewed by a leading scientific journal. In it, he predicted how our universe would eventually fade to darkness as the stars run out of energy.

Alongside Professor Thomas Hertog of Belgium's KU Leuven University, Hawking also proposed a way in which scientists might be able to find alternate universes by using probes on space ships. This would allow humans to attain a more accurate understanding of our own universe, decipher what else is out there and ultimately realize our place in the cosmos.

"He has often been nominated for the Nobel and should have won it. Now he never can," Hertog told The Sunday Times in an interview published Sunday.

'Intelligent life may be watching'

Hawking, who was perhaps best known for his work on black holes and the theory of relativity, had previously posited the idea that Earth would turn into a giant ball of fire by 2600. Therefore, humans would eventually need to colonize another planet or face extinction, he said.

In 2015, Hawking joined Russian billionaire Yuri Milner to launch a project that aimed to use high-powered computers to listen for aliens. The project, known as Breakthrough Initiatives, supports SETI@home, a scientific experiment based at the University of California, Berkeley. It uses computers to scan the skies to look for life.

"Somewhere in the cosmos, perhaps, intelligent life may be watching these lights of ours aware of what they mean," Hawking said. "Or do our lights wander a lifeless cosmos, unseen beacons announcing that here on our rock, the universe discovered its existence?"


— CNBC's Arjun Kharpal contributed to this report.
source : (www.cnbc.com)

Physicists Turn a Single Atom Into a Mirror

You can't get much smaller than this: Physicists have fashioned a mirror from a single atom. The advance might lead to an atom-sized transistor for light, and experts say it bodes well for broader efforts to shrink optical elements to the nanometer scale.

"In terms of the basic physics, it's incredibly cute," says Christian Kurtsiefer, an experimental physicist at the National University of Singapore, who was not involved in the work. "It's a very striking effect because you wouldn't necessarily expect that a single atom would exert a lot of influence on the flow of light."

In fact, the atom effectively reflects less than 1% of the light that hits it. So to detect the reflection, Gabriel Hétet, Rainer Blatt, and colleagues at the University of Innsbruck in Austria relied on a wave effect known as interference. They fashioned a device called a Fabry-Pérot interferometer, which ordinarily consists of two mirrors facing each other. Laser light of a fixed wavelength shines on the back of one mirror and some leaks through the mirror, entering the "cavity" between the mirrors. A small amount of light then leaks through the second mirror, while most of it reflects back toward the first. The reflected light can make multiple roundtrips between the mirrors. Each time, a little more light can leak through the second, farther mirror. (A similar effect takes place at the first mirror, too.)

Here's where the interference comes in. If the roundtrip distance between the mirrors equals a multiple of the light's wavelength, then all the light waves leaking through the second mirror will be in sync and reinforce each other, greatly increasing the transmission. If this roundtrip distance is slightly different, all those waves will be out of sync and cancel each other out, reducing the transmission. So the amount of transmitted light goes up and down as the distance between the mirrors increases.

Hétet, Blatt, and colleagues replaced the second mirror with a single atom—actually a barium ion. To focus the light on the atom and collect the light bouncing off it, they put a 1.5-centimeter-wide lens between it and the mirror. To hold the ion steady 14 millimeters away from the mirror, they captured it in an electronic trap and used other laser beams to cool it so that it jiggled no more than 20 nanometers from the trap's center. Finally, they tuned the wavelength of the light entering the interferometer so that it could "excite" the atom from a particular low-energy state to a higher-energy one. Without such a light-atom interaction, the atom can't affect the light.

The interferometer wasn't perfect. As the researchers moved the ion away from the mirror, the amount of light coming through the system varied by about 6%, they report in a paper to be published in Physical Review Letters. In a standard Fabry-Pérot, the transmitted light will fall to essentially zero if the roundtrip distance between the mirrors is just a little off the required spacing. Still, the data show the atom working as a mirror.

So what's this tiny mirror good for? In principle, it helps extend a theoretical approach known as cavity quantum electrodynamics. A cavity like a Fabry-Pérot can change the vacuum of empty space to allow only certain quantum states of light to exist between its mirrors—those with correct wavelengths. The new experiment shows that a mirror and a single atom can exert the same sort of influence.

More practically, with a better lens to increase the effective reflectivity of the atom, the device might make a building block for an optical version of electronics. "One can think of moving the mirror to make the atom transmit or reflect the light, which would make it a transistor" for light, Hétet says. In principle, such an optical system could be faster and more efficient than current electronics. A tack better suited to all-optical systems would be to use a single photon from yet another laser to control the atom's reflectivity by changing its internal state, Kurtsiefer says: "That's the hard part."

The experiment comes as good news to scientists striving to make ever smaller optical devices, says David Kielpinski, a physicist at Griffith University in Brisbane, Australia. Physicists don't fully understand whether the properties of optical devices will change as the devices shrink to atomic scale, Kielpinski says: "This work tells you, 'Hey, it's okay to build optical components out of a few atoms. There's nothing lurking around the corner to kill that enterprise.' "