Posts Tagged ‘physics’
Working Tractor Beam Can Move Objects 5 Feet With Just Light
Using only light, Australian researchers say they are able to move small particles almost five feet through the air. It’s more than 100 times the distance achieved by existing optical “tweezers,” the researchers say.
Not quite a simple grabby tractor beam, the new system works by shining a hollow laser beam at an object and taking advantage of air-temperature differences to move it around.
Moving objects with powerful light is not new — researchers have long been using optical tweezers to pluck bacteria-sized particles and move them a few millimeters. The U.S. Secretary of Energy, Steven Chu, won his Nobel Prize for work with optical tweezers. But Andrei Rhode and colleagues at the Australian National University say their new laser device can move glass objects hundreds of times bigger than bacteria, and shove them a meter and a half (5 feet) or more. Rhode says the 1.5-meter limit was only because of the size of the table where he placed his lasers — he thinks he can move objects up to 10 meters, or about 30 feet.
It works by shining a hollow laser beam around small glass particles, as Inside Science explains. The air around the particle heats up, but the hollow center of the beam stays cool. The heated air molecules keep the object balanced in the dark center. But a small amount of light sneaks into the hollow, warming the air on one side of the object and nudging it along the length of the laser beam. Researchers can change the speed and direction of the glass object by changing the lasers’ brightness.
The system needs heated air or gas to work, so in its present incarnation it wouldn’t work in space — sorry, Star Wars fans. But it could be used for a variety of purposes on Earth, like biological research or movement of hazardous materials.
DARPA Wants Portable Atomic Clocks for Better Synchronicity
DARPA’s Quantum Assisted Sensing and Readout (QuASAR) program aims to take high-performance atomic clocks like the National Institute of Standards and Technology’s NIST-F1, the massive room-sized clock housed in a lab in Boulder, Colo. Doing so won’t be any easier than many other challenges DARPA brings to the table, but the agency thinks advances in nanoelectromechanical systems (NEMS) resonators and nitrogen-vacancy (NV) centers in diamonds that exhibit single-atom-like properties could create a close analog to an atomic clock in a miniature, portable package.
Atomic clocks don’t lose seconds or even fractions of seconds over time (well, that’s not entirely true, but time lost is negligible; NIST-F1 will neither gain nor lose a second in 60 million years), and that opens up major possibilities for syncronisity. Such portable clocks would allow for communications systems that are far more secure less susceptible to jamming and GPS positioning that is unrivaled. DARPA also thinks they might lead to precision sensors unrivaled in resolution and sensitivity.
Fundamental Physics Laws Change Depending on When and Where You Are, New Study Says
The paper, recently submitted to Physical Review Letters and posted to the physics arXiv, suggests the fine structure constant is not actually constant at all. This could mean that if we were in a different place or time period, atoms would not stay together and nothing — neither planets nor people — could exist.
A team led by John Webb at the University of New South Wales, Australia, has been studying whether the fine structure constant, otherwise known as alpha, changes over time. Alpha is a special number that essentially describes the strength of the electromagnetic force. The famous physicist Richard Feynman called its value "one of the greatest damn mysteries of physics." If it is not 1/137.036, things fall apart.
If alpha was different in the past, the universe might have looked different, too, which could be determined by looking at distant interstellar gases and how they absorb light. Observations by Webb and others at the Keck Observatory in Hawaii suggest that this is exactly the case — over time, alpha has changed ever so slightly.
Competing studies did not find the same result, however, so this is still a controversial idea. But it’s a fair bet Webb’s follow-up is even more tendentious: He says alpha also changes over space. According to his theory, we’re smack in the Goldilocks zone, where alpha is exactly the right value to make matter possible.
This paper happened because Webb and his team wanted to reexamine their Keck findings, which suggested alpha was a tiny bit smaller about 9 billion years in the past. They went to the Very Large Observatory in Chile to check it out, and were shocked by what they saw: the further they looked, the bigger alpha got. The discrepancy is even stranger given the two telescopes’ positions: they are in two different hemispheres, so they look in two different directions.
So, to recap: in one direction, alpha was once smaller; in exactly the opposite direction, it was once bigger. This implies that alpha continuously varies throughout space. As Technology Review’s physics blog puts it, that's a mind-blowing result. If it’s true and can be verified, it could mean the universe is much larger than what we can see, and that the laws of physics vary within it.
It would not be possible for our type of life to exist in a place where alpha were any different. So here’s to here and now.
Researchers Devise the First Experimental Test of Controversial, Confusing String Theory
String theory elegantly reconciles the otherwise competing rules of quantum mechanics and general relativity. It’s the most widely accepted unified field theory, but it remains controversial. It basically posits that electrons and quarks are not objects, but one-dimensional strings, whose oscillation gives them their observed qualities. The most fun element of string theory is the requirement that the universe has about a dozen dimensions, rather than the usual four (length, width, height and time).
M-theory, the dominant version of string theory, holds that the universe is made up of unfathomably small slices of a 2-dimensional membrane, wriggling in 11-dimensional space.
These bizarre ideas are widely accepted by many theoretical physicists, but the problem is that they can’t be tested — how do you examine an 11th dimension? The field has suffered a backlash in recent years partly for this reason, as some scientists say a theory is not a theory if its predictions can’t be studied in a lab.
Well, now they can, according to professor Mike Duff of the theoretical physics department at Imperial College London. He is lead author of a paper to be published tomorrow in Physical Review Letters, which explains how string theory math can be used to predict quantum entanglement.
Duff said he was at a conference in Tasmania when a colleague presented some mathematical formulas describing entanglement of multiple quantum bits. The equations looked familiar. Upon returning home, Duff checked his notebooks from a few years earlier, and realized the formulas were the same as those he developed to use string theory to describe black holes.
This is completely unexpected, he said. There is no obvious reason why the insanely complex mathematics underlying string theory can also be used to predict the behavior of entangled quantum systems.
“This may be telling us something very deep about the world we live in, or it may be no more than a quirky coincidence,” he said.
Either way, it’s useful, he added. Using string theory math, Duff predicted the pattern that would occur when four quantum bits are entangled with each other. This can be measured in a lab, and the results will demonstrate whether string theory actually works.
Right now, the best hope for string theory tests comes from CERN’s Large Hadron Collider, which is designed to find the tiniest elementary particles that make up matter. It’s theoretically possible that LHC experiments will uncover supersymmetric particles — one element of string theory — or bounce a graviton into a higher dimension, which could help prove M-theory. But testing the fuzzy math that predicts these behaviors will be much easier.
Coming Generation of Lasers May Be the Most Powerful Lasers That Will Ever Lase
The theoretical energy ceiling for lasers is approaching
That finite limit on how intense a laser can get is hypothesized to exist because, at sufficiently high energies, matter can be created out of light.
When a high-powered laser fires, causing photons to impact electrons at a tremendous velocity, it is possible for matter -- a positron-electron pair -- to be created by the impact, as was demonstrated in a Stanford experiment in 1997. When such matter is created with a sufficiently high energy, it in turn can emit photons that move fast enough that they create their own matter. This cascade effect can have as much energy as the laser itself does, and result in the destruction of the laser.
It is predicted that the effect will be visible in the ELI project and other lasers currently being built.
For the First Time, Scientists Watch Electrons Move in Real Time
Using ultra-short flashes of laser light, scientists from the Max Planck Institute of Quantum Optics in Germany and Lawrence Berkeley National Laboratory in Berkeley, Calif., were able to time oscillations between valence electrons' quantum states.
Chemical reactions happen because of the dynamics of valence electrons, the ones in the outermost orbit of an atom. If you can watch them move, you can understand their mechanics and learn how they combine with other atoms to make up everything around us. But electrons move pretty fast, so this has been impossible until now.
The team used lasers that can work in the 100-attosecond time scale -- an attosecond is 10-18 seconds, a quintillionth of a second. They measured the movement of valence electrons in a form of ionized krypton that had one electron removed.
Berkeley Lab's news site provides some in-depth descriptions, but basically what happened is that scientists measured the continued flopping of electrons between two quantum states. These valence shell oscillations cycled in a little over six femtoseconds. Using much faster attosecond laser pulses, the team was able to essentially capture this oscillation in action. The work is reported in this week's edition of the journal Nature.
The Berkeley Lab test simply proves that scientists can see these electrons move. But the finding can be applied to any problem in the physics and chemistry of liquids, solids, biological systems -- basically everything, according to Stephen Leone of Berkeley Lab's Chemical Sciences Division.
"(It will) allow us to unravel processes within and among atoms, molecules, and crystals on the electronic timescale," he says.
As Berkeley Lab's news writer notes, this would have been previously impossible with the "comparatively languorous femtosecond timescale."
German Scientists Measure How Fast an Electron Jumps, the Shortest Time Interval Ever Measured
During photoemission – the expulsion of electrons from an atom by bombarding them with high-energy light – it’s always been assumed that there is no delay between the photons’ impact and the breaking loose of the target electron. But a group of German researchers in collaboration with Greek, Austrian, and Saudi Arabian colleagues decided to challenge that assumption with extremely sensitive time measurement tech.
The team bombarded atoms of neon gas with near-infrared laser light in 10-15 second pulses and ultraviolet pulses of far shorter durations of just 180 attoseconds (remember, an attosecond is one billionth of one billionth of one second). The near-IR light served as an attosecond chronograph, measuring the time of UV impact and the time the electrons exited their orbits.
Their findings turned up two interesting results. For one, they found that electron ejection is not a “time zero” action as once presumed, but that excited electrons hesitate very, very briefly before leaving the atom. But perhaps more interesting, they found that electrons from different orbitals behaved differently, leaving the atom at slightly different times even though they were impacted simultaneously.
The researchers are not exactly sure why this is, but it likely has to do with some small, overlooked influence that electrons exert over one another that is different that the forces exerted on electrons by their nuclei. If that’s the case, the tiny time lag could have big consequences for physics, a discipline ruled by the interactions between atoms and the behavior of electrons. Until they figure all that out, they can at least take pride in their 20-attosecond record for the shortest time interval ever directly measured.