Posts Tagged ‘physics’
Math is Pretty
Sunday, November 18th, 2007The Nothing is Coming
Thursday, August 23rd, 2007There is a hole in the universe.
Solid Light
Thursday, May 10th, 2007Researchers from the Universities of Melbourne and Cambridge have unveiled a new theory that shows light can behave like a solid.“Solid light will help us build the technology of this century,” says Dr Andrew Greentree of the School of Physics at the University of Melbourne.
Dr Greentree and colleagues Jared Cole and Professor Lloyd Hollenberg of the University of Melbourne with Dr Charles Tahan of the University of Cambridge made their ‘solid light’ breakthrough using tools more commonly used to study matter.
“Solid light photons repel each other as electrons do. This means we can control photons, opening the door to new kinds of faster computers,” says Dr Greentree.
Cloaking Device Activated
Monday, April 2nd, 2007Researchers using nanotechnology have taken a step toward creating an “optical cloaking” device that could render objects invisible by guiding light around anything placed inside this “cloak.”The Purdue University engineers, following mathematical guidelines devised in 2006 by physicists in the United Kingdom, have created a theoretical design that uses an array of tiny needles radiating outward from a central spoke. The design, which resembles a round hairbrush, would bend light around the object being cloaked. Background objects would be visible but not the object surrounded by the cylindrical array of nano-needles, said Vladimir Shalaev, Purdue’s Robert and Anne Burnett Professor of Electrical and Computer Engineering.
The design does, however, have a major limitation: It works only for any single wavelength, and not for the entire frequency range of the visible spectrum, Shalaev said.
“But this is a first design step toward creating an optical cloaking device that might work for all wavelengths of visible light,” he said.
[SNIP]
Leonhardt says in his commentary that creating a cloak for rendering total invisibility in the entire visible spectrum would require “further advances in optical metamaterials, new combinations of nanotechnology with highly abstract ideas …”
Liquid Light
Tuesday, March 27th, 2007Scientists have figured out how to create a jet of liquid with nothing but the power of light.They shined a laser beam through a soapy liquid, producing a long jet that eventually broke up into droplets.
“I thought this was just so weird because I know when liquid is supposed to break up, and this one isn’t doing it,” said study team member Wendy Zhang, an assistant professor in physics at the University of Chicago.
Dancing Electrons, a New Matter Entirely
Saturday, March 17th, 2007The first hint that a new type of matter may exist came in 1983. “Twenty five years ago we thought we understood everything about how matter changes phase,” says Wen. “Then along came an experiment that opened up a whole new world.”In the experiment, electrons moving in the interface between two semiconductors behaved as though they were made up of particles with only a fraction of the electron’s charge. This so-called fractional quantum hall effect (FQHE) suggested that electrons may not be elementary particles after all. However, it soon became clear that electrons under certain conditions can congregate in a way that gives them the illusion of having fractional charge – an explanation that earned Laughlin, Horst Störmer and Daniel Tsui the Nobel prize
Wen suspected that the effect could be an example of a new type of matter. Different phases of matter are characterised by the way their atoms are organised. In a liquid, for instance, atoms are randomly distributed, whereas atoms in a solid are rigidly positioned in a lattice. FQHE systems are different. “If you take a snapshot of the position of electrons in an FQHE system they appear random and you think you have a liquid,” says Wen. But step back, and you see that, unlike in a liquid, the electrons dance around each other in well-defined steps.
It is as if the electrons are entangled. Today, physicists use the term to describe a property in quantum mechanics in which particles can be linked despite being separated by great distances. Wen speculated that FQHE systems represented a state of matter in which entanglement was an intrinsic property, with particles tied to each other in a complicated manner across the entire material.
This led Wen and Levin to the idea that there may be a different way of thinking about matter. What if electrons were not really elementary, but were formed at the ends of long “strings” of other, fundamental particles? They formulated a model in which such strings are free to move “like noodles in a soup” and weave together into huge “string-nets”.
[SNIP]
From this, the researchers made another leap. Could the entire universe be modelled in a similar way? “Suddenly we realised, maybe the vacuum of our whole universe is a string-net liquid,” says Wen. “It would provide a unified explanation of how both light and matter arise.” So in their theory elementary particles are not the fundamental building blocks of matter. Instead, they emerge from the deeper structure of the non-empty vacuum of space-time.
“Wen and Levin’s theory is really beautiful stuff,” says Michael Freedman, 1986 winner of the Fields medal, the highest prize in mathematics, and a quantum computing specialist at Microsoft Station Q at the University of California, Santa Barbara. “I admire their approach, which is to be suspicious of anything – electrons, photons, Maxwell’s equations – that everyone else accepts as fundamental.”
Other theories that try to explain the same phenomena abound, of course; Wen and Levin realise that the burden of proof is on them. It may not be far off. Their model predicts specific arrangements of atoms in the new state of matter, which they dub the “string-net liquid”, and Joel Helton’s group at MIT might have found it.
Helton was aware of Wen’s work and decided to look for such materials. Trawling through geology journals, his team spotted a candidate – a dark green crystal that geologists stumbled across in the mountains of Chile in 1972. “The geologists named it after a mineralogist they really admired, Herbert Smith, labelled it and put it to one side,” says team member Young Lee. “They didn’t realise the potential herbertsmithite would have for physicists years later.”
The Birth (and Death) of Light
Friday, March 16th, 2007For the first time the birth, life and death of a single photon – a particle of light – has been “watched” in real time.Previously, scientists were restricted to momentary glances because the mere act of measurement absorbed and destroyed the delicate quantum particles.
Now, Serge Haroche and colleagues at the École Normale Supérieure in Paris, France, have succeeded in tracking photons over an average lifetime of 0.13 seconds – long enough for a photon to travel one-tenth of the way to the Moon.
At the heart of their remarkable achievement lies a small box-like cavity, walled with ultra-reflective, superconducting mirrors, which is cooled to just 0.5° above absolute zero (-273.15°C). Photons appear and disappear randomly within the cavity due to tiny energy fluctuations in space that cause quantum particles to blink in and out of existence. However, once there, the photon is trapped, bouncing billions of times between the mirrored walls before it decays.
True in Practice, but is it true in theory?
Wednesday, February 7th, 2007A pulse of light can be stopped, transported, and restarted again using a cloud of super-cold atoms, US researchers have shown. The technique could ultimately be used for advanced computing devices or gravity detectors.The experiments demonstrate physicists’ increasing ability to manipulate light. Being able to control it in this way could be useful for optical or quantum computers, the team suggests.
“The first time I read this paper, I didn’t believe it,” says Michael Fleischhauer, a theoretical physicist at the University of Kaiserslautern in Germany. “Even though theory tells us it should be possible, actually doing it is something else.”
Fuse On!
Monday, January 15th, 2007Designed to replicate the sun’s energy generating process, the Experimental Advanced Superconducting Tokamak fusion reactor recently garnered positive results in tests being conducting at China’s Institute of Plasma Physics, the Chinese news agency Xinhua reported.‘The new tests show the reactor is very reliable, and we can repeat the experiments,’ institute official Wu Songtao said.
With tests set to continue until Feb. 10, the experiments will reveal exactly how far the project is from its final goal of creating plasma that can last for 1,000 seconds while giving off its own energy.
While many have disputed the project’s ability to create such an energy source, Xinhua said many scientists maintain such a fusion reactor could lesson China’s energy crisis by providing cleaner endless energy at a significantly lower cost.
Invisible Structures
Monday, January 8th, 2007The distribution of dark matter has been mapped in 3D for the first time, revealing how the mysterious substance has evolved over the lifetime of the universe. The results confirm that dark matter provided the scaffolding that allowed ordinary matter to clump together to form galaxies and clusters of galaxies.Dark matter is an invisible substance that betrays its presence through the gravitational tug it exerts on ordinary matter. It is six times more abundant than ordinary matter and is thought to have seeded the first distinct structures in the universe, which began as a very uniform soup of matter.
Computer simulations suggest that the formation of dark matter clumps attracted surrounding gas, which then condensed to form galaxies and galaxy clusters. But this dark matter clumping process had never been confirmed observationally.
Now, astronomers have mapped the changing distribution of both dark matter and ordinary matter over time. Nick Scoville, of Caltech in Pasadena, US, led the Cosmic Evolution Survey (COSMOS), which combined data from three of the world’s leading observatories to produce the map.
The key to determining the dark matter distribution is an effect called gravitational lensing, by which light rays from a distant object such as a galaxy are bent by the gravity of an intervening concentration of matter. Although dark matter cannot be seen directly, its presence can be inferred by the way its gravity distorts the images of galaxies behind it.
