Not Just Science Fiction: 'Electromagnetic Wormhole' Possible, Say Mathematicians

Source:

http://www.sciencedaily.com/releases/2007/10/071012160144.htm

Science Daily — The team of mathematicians that first created the mathematics behind the "invisibility cloak" announced by physicists last October has now shown that the same technology could be used to generate an "electromagnetic wormhole."

In the study, which is to appear in the Oct. 12 issue of Physical Review Letters, Allan Greenleaf, professor of mathematics at the University of Rochester, and his coauthors lay out a variation on the theme of cloaking. Their results open the possibility of building a sort of invisible tunnel between two points in space.
"Imagine wrapping Harry Potter's invisibility cloak around a tube," says Greenleaf. "If the material is designed according to our specifications, you could pass an object into one end, watch it disappear as it traveled the length of the tunnel, and then see it reappear out the other end."
Current technology can create objects invisible only to microwave radiation, but the mathematical theory allows for the wormhole effect for electromagnetic waves of all frequencies. With this in mind, Greenleaf and his coauthors propose several possible applications. Endoscopic surgeries where the surgeon is guided by MRI imaging are problematical because the intense magnetic fields generated by the MRI scanner affect the surgeon's tools, and the tools can distort the MRI images. Greenleaf says, however, that passing the tools through an EM wormhole could effectively hide them from the fields, allowing only their tips to be "visible" at work.
To create cloaking technology, Greenleaf and his collaborators use theoretical mathematics to design a device to guide the electromagnetic waves in a useful way. Researchers could then use these blueprints to create layers of specially engineered, light-bending, composite materials called metamaterials.
Last year, David R. Smith, professor of electrical and computer engineering at Duke's Pratt School, and his coauthors engineered an invisibility device as a disk, which allowed microwaves to pass around it. Greenleaf and his coauthors have now employed more elaborate geometry to specify exactly what properties are demanded of a wormhole's metamaterial in order to create the "invisible tunnel" effect. They also calculated what additional optical effects would occur if the inside of the wormhole was coated with a variety of hypothetical metamaterials.
Assuming that your vision was limited to the few frequencies at which the wormhole operates, looking in one end, you'd see a distorted view out the other end, according the simulations by Greenleaf and his coauthors. Depending on the length of the tube and how often the light bounced around inside, you might see just a fisheye view out the other end, or you might see an Escher-like jumble.
Greenleaf and his coauthors speculated on one use of the electromagnetic wormhole that sounds like something out of science fiction. If the metamaterials making up the tube were able to bend all wavelengths of visible light, they could be used to make a 3D television display. Imagine thousands of thin wormholes sticking up out of a box like a tuft of long grass in a vase. The wormholes themselves would be invisible, but their ends could transmit light carried up from below. It would be as if thousands of pixels were simply floating in the air.
But that idea, Greenleaf concedes, is a very long way off. Even though the mathematics now says that it's possible, it's up to engineers to apply these results to create a working prototype.
Greenleaf's coauthors are Matti Lassas, professor of mathematics at the Helsinki University of Technology; Yaroslav Kurylev, professor of mathematics at the University College, London; and Gunther Uhlmann, Walker Family Endowed Professor of Mathematics at the University of Washington.
Note: This story has been adapted from material provided by University of Rochester.

Fausto Intilla

www.oloscience.com

Physicist Defends Einstein's Theory And 'Speed Of Gravity' Measurement

Source:

http://www.sciencedaily.com/releases/2007/10/071003130816.htm

Science Daily — Scientists have attempted to disprove Albert Einstein's theory of general relativity for the better part of a century. After testing and confirming Einstein's prediction in 2002 that gravity moves at the speed of light, a professor at the University of Missouri-Columbia has spent the past five years defending the result, as well as his own innovative experimental techniques for measuring the speed of propagation of the tiny ripples of space-time known as gravitational waves.
Sergei Kopeikin, associate professor of physics and astronomy in the College of Arts and Science, believes that his latest article, "Gravimagnetism, causality, and aberration of gravity in the gravitational light-ray deflection experiments" published along with Edward Fomalont from the National Radio Astronomical Observatory, arrives at a consensus in the continuing debate that has divided the scientific community.
An experiment conducted by Fomalont and Kopeikin five years ago found that the gravity force of Jupiter and light travel at the same speed, which validates Einstein's suggestion that gravity and electromagnetic field properties, are governed by the same principle of special relativity with a single fundamental speed. In observing the gravitational deflection of light caused by motion of Jupiter in space, Kopeikin concluded that mass currents cause non-stationary gravimagnetic fields to form in accordance with Einstein's point of view.
Einstein believed that in order to measure any property of gravity, one has to use test particles. "By observing the motion of the particles under influence of the gravity force, one can then extract properties of the gravitational field," Kopeikin said. "Particles without mass -- such as photons -- are particularly useful because they always propagate with constant speed of light irrespectively of the reference frame used for observations."
"The property of gravity tested in the experiment with Jupiter also is called causality. Causality denotes the relationship between one event (cause) and another event (effect), which is the consequence (result) of the first. In the case of the speed of gravity experiment, the cause is the event of the gravitational perturbation of photon by Jupiter, and the effect is the event of detection of this gravitational perturbation by an observer.
"The two events are separated by a certain interval of time which can be measured as Jupiter moves, and compared with an independently-measured interval of time taken by photon to propagate from Jupiter to the observer. The experiment found that two intervals of time for gravity and light coincide up to 20 percent. Therefore, the gravitational field cannot act faster than light propagates."
Other physicists argue that the Fomalont-Kopeikin experiment measured nothing else but the speed of light. "This point of view stems from the belief that the time-dependent perturbation of the gravitational field of a uniformly moving Jupiter is too small to detect," Kopeikin said. "However, our research article clearly demonstrates that this belief is based on insufficient mathematical exploration of the rich nature of the Einstein field equations and a misunderstanding of the physical laws of interaction of light and gravity in curved space-time."
The research paper that discusses the gravimagnetic field appears in the October edition of Journal of General Relativity and Gravitation.
Note: This story has been adapted from material provided by University of Missouri-Columbia.

Fausto Intilla
www.oloscience.com

Gamma Ray Lasers? Positronium Created In The Lab

Source:

http://www.sciencedaily.com/releases/2007/09/070912154633.htm

Science Daily — Physicists at UC Riverside have created molecular positronium, an entirely new object in the laboratory. Briefly stable, each molecule is made up of a pair of electrons and a pair of their antiparticles, called positrons.

The research paves the way for studying multi-positronium interactions -- useful for generating coherent gamma radiation -- and could one day help develop fusion power generation as well as directed energy weapons such as gamma-ray lasers. It also could help explain how the observable universe ended up with so much more matter than "antimatter."
The researchers made the positronium molecules by firing intense bursts of positrons into a thin film of porous silica, which is the chemical name for the mineral quartz. Upon slowing down in silica, the positrons were captured by ordinary electrons to form positronium atoms.
Positronium atoms, by nature, are extremely short-lived. But those positronium atoms that stuck to the internal pore surfaces of silica, the way dirt particles might cling to the inside surface of the holes in a sponge, lived long enough to interact with one another to form molecules of positronium, the physicists found.
"Silica acts in effect like a useful cage, trapping positronium atoms," said David Cassidy, the lead author of the research paper and an assistant researcher working in the laboratory of Allen Mills, a professor of physics, the research paper's coauthor. "This is the first step in our experiments. What we hope to achieve next is to get many more of the positronium atoms to interact simultaneously with one another -- not just two positronium atoms at a time."
When an electron meets a positron, their mutual annihilation may ensue or positronium, a briefly stable, hydrogen-like atom, may be formed. The stability of a positronium atom is threatened again when the atom collides with another positronium atom. Such a collision of two positronium atoms can result in their annihilation, accompanied by the production of a powerful and energetic type of electromagnetic radiation called gamma radiation, or the creation of a molecule of positronium, the kind Cassidy and Mills observed in their lab.
"Their research is giving us new ways to understand matter and antimatter," said Clifford M. Surko, a professor of physics at UC San Diego, who was not involved in the research. "It also provides novel techniques to create even larger collections of antimatter that will likely lead to new science and, potentially, to important new technologies."
Matter, the "stuff" that every known object is made of, and antimatter cannot co-exist close to each other for more than a very small measure of time because they annihilate each other to release enormous amounts of energy in the form of gamma radiation. The apparent asymmetry of matter and antimatter in the visible universe is an unsolved problem in physics.
Currently, antimatter finds use in medicine where it helps identify diseases with the Positron Emission Tomography or PET scan.
Cassidy and Mills plan to work next on using a more intense positron source to generate a "Bose-Einstein condensate" of positronium -- a collection of positronium atoms that are in the same quantum state, allowing for more interactions and gamma radiation. According to them, such a condensate would be necessary for the development of a gamma-ray laser.
Study results appear in the Sept. 13 issue of Nature.
Their research was funded by the National Science Foundation.
Note: This story has been adapted from a news release issued by University of California - Riverside.

Fausto Intilla

www.oloscience.com

Physicists Establish 'Spooky' Quantum Communication

Source:

http://www.sciencedaily.com/releases/2007/09/070905133621.htm

Science Daily — Physicists at the University of Michigan have coaxed two separate atoms to communicate with a sort of quantum intuition that Albert Einstein called "spooky."
In doing so, the researchers have made an advance toward super-fast quantum computing. The research could also be a building block for a quantum internet.
Scientists used light to establish what's called "entanglement" between two atoms, which were trapped a meter apart in separate enclosures (think of entangling like controlling the outcome of one coin flip with the outcome of a separate coin flip).
"This linkage between remote atoms could be the fundamental piece of a radically new quantum computer architecture," said Professor Christopher Monroe, the principal investigator who did this research while at U-M, but is now at the University of Maryland. "Now that the technique has been demonstrated, it should be possible to scale it up to networks of many interconnected components that will eventually be necessary for quantum information processing."
David Moehring, the lead author of the paper who did this research as a U-M graduate student, says the most important feature of this experiment is the distance between the two atoms. Moehring graduated and now has a position at the Max-Planck-Institute for Quantum Optics in Germany.
"The separation of the qubits in our entangled state is the most important feature," Moehring said. "Localized entanglement has been performed in ion trap qubits in the past, but if one desires to build a scalable quantum computer network (or a quantum internet), the creation of entanglement schemes between remotely entangled qubit memories is necessary."
In this experiment, the researchers used two atoms to function as qubits, or quantum bits, storing a piece of information in their electron configuration. They then excited each atom, inducing electrons to fall into a lower energy state and emit one photon, or one particle of light, in the process.
The atoms, which were actually ions of the rare-earth element ytterbium, are capable of emitting two different types of photon of different wavelengths. The type of photon released by each atom indicates the particular state of the atom. Because of this, each photon was entangled with its atom.
By manipulating the photons emitted from each of the two atoms and guiding them to interact along a fiber optic thread, the researchers were able to detect the resulting photon clicks and entangle the atoms. Monroe says the fiber optic thread was necessary to establish entanglement of the atoms, but then the fiber could be severed and the two atoms would remain entangled, even if one were "(carefully) taken to Jupiter."
Each qubit's information is like a single bit of information in a conventional computer, which is represented as a 0 or a 1. Things get weird on the quantum scale, though, and a qubit can be either a 0, a 1, or both at the same time, Monroe says. Scientists call this phenomenon "superposition." Even weirder, scientists can't directly observe superposition, because the act of measuring the qubit affects it and forces it to become either a 0 or a 1.
Entangled particles can default to the same position once measured, for example always ending in 0,0 or 1,1.
"When entangled objects are measured, they always result in some sort of correlation, like always getting two coins to come up the same, even though they may be very far apart," Monroe said. "Einstein called this 'spooky action-at-a-distance,' and it was the basis for his nonbelief in quantum mechanics. But entanglement exists, and although very difficult to control, it is actually the basis for quantum computers."
Scientists could set the position of one qubit and know that its entangled mate will follow suit.
Entanglement provides extra wiring between quantum circuits, Monroe says. And it allows quantum computers to perform tasks impossible with conventional computers. Quantum computers could transmit provably secure encrypted data, for example. And they could factor numbers incredibly faster than today's machines, making most current encryption technology obsolete (most encryption today is based on the inability for man or machine to factor large numbers efficiently).
A paper on the findings appears in the Sept. 6 edition of the journal Nature. The paper is titled "Entanglement of single atom quantum bits at a distance."
Note: This story has been adapted from a news release issued by University of Michigan.

Fausto Intilla
www.oloscience.com