80beats » Physics & Math

Scientist Smackdown: Are a Sprinter’s Prostethic Legs an Unfair Advantage?

Andrew Moseman — Thu, 19 Nov 2009 15:59:16 +0000

If you read this blog last week, you might have seen us cover a study suggesting that South African sprinter Oscar Pistorius ought to be allowed to compete in the same track and field events as everyone else because his prosthetic legs confer no advantage over a sprinter with biological legs. But if you saw a study cited by the Associated Press and many other publications yesterday, you might think that Pistorius would soon be banned from competitions, because his “blades” let him swing his legs far faster than even the world’s fastest man, Usain Bolt. So what the heck is going on?

The AP’s study isn’t actually a “study,” per se. Rather, what the Journal of Applied Physiology published was a point-counterpoint (pdf), now freely available for anyone to read. In in, Peter Weyand and Matthew Bundle argue that Pistorius’ prosthetics are a huge advantage, particularly in what matters most: how fast he can move his legs. Weyand and Bundle say that the lightweight blades allow Pistorius “to reposition his limbs 15.7 percent more rapidly than five of the most recent former world-record holders in the 100-meter dash” [AP].

There is, however, a counterpoint to this argument in the journal piece that yesterday’s news reports neglected, coauthored by Alena Grabowski of the MIT Media Lab (who led the research on Pistorius’ blades that 80beats covered last week). Her team has found that the limiting factor determining an athlete’s top speed was how hard the foot or prosthesis hit the ground. Their study showed this “ground force” was around 9% lower in the prosthetic limb versus the unaffected leg [The Guardian]. Grabowski’s research focused on professional runners with only one prosthetic leg.

No matter, Weyand and Bundle say in a rebuttal to the counterpoint: because Pistorius swings his legs so quickly (about .28 seconds per leg, as opposed to the .36 seconds of world-class sprinters with biological legs), he needs 20 percent less ground force than an ordinary runner would to maintain the same speed. Weyand told DISCOVER that the MIT team’s research is probably correct about speed and power when it comes to runners with only one prosthetic. “One limb can’t go faster than the other,” or the runner would go in a circle. But a runner like Pistorius with two prosthetics can learn to swing both legs at the “off-the-charts” speed of .28 seconds, he says, gaining a clear advantage.

Grabowski was understandably miffed at her side’s counterargument being left out of news reports. “We’re all sort of shaking our heads,” she said. She also questioned the validity of Weyand and Bundle’s findings, saying in an email to DISCOVER that they represent an opinion and not a peer-reviewed study, that they don’t consider the starting blocks and turning inherent in a 400-meter race, and Weyand and Bundle’s assertion that Pistorius’ blades take 10 seconds off his 400-meter time “is ridiculous and not based on data.”

But, Weyand tells DISCOVER, he and Bundle got their data during direct observations of Pistorius last year, during the time he was attempting to qualify for the Beijing Olympics. At that time they arrived at the same kind of conclusion Grabowski’s side has arrived at now—that the sprinter ought not be banned. The reason for this odd twist in the story, Weyand says, is that he and Bundle were brought in by Pistorius’ law firm during a hearing last May on the question of whether to overturn a ban on Pistorius, but the hearing could only consider the evidence used to enact the ban in the first place. So, Weyand tells DISCOVER, he and Bundle’s were advocating analysis suggested the ban be overturned because its basis was shoddy insufficient scientific evidence, and at the same time their own studies convinced them that he did have a clear advantage.

To make this affair even stranger, both sides—Weyand and Bundle’s team, and Grabowski’s—all co-authored a less controversial paper earlier this year in the same journal. However, Bundle tells DISCOVER, they left the question of advantage or no advantage out of that paper because they couldn’t agree, and published this point-counterpoint instead. “The comparisons and analysis that Peter and I present in the point-counterpoint are novel, in part because our co-authors prevented them from being included in the manuscript that appeared in June,” he says. As for peer review, Bundle says his argument did receive this treatment, because the journal’s standards consider the editors’ approval of an article to be an appropriate review.

This scientist smackdown isn’t going away: Grabowski told DISCOVER she would issue a press release in response to Weyand and Bundle’s, and continue her prosthesis research. Though if there’s one thing both sides can agree on, it’s that Pistorius is a remarkable athlete, advantage or not. “What he does as an athletic feat is really an amazing thing,” Weyand says.

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Image: flickr/Elvar Freyr

Rosetta Photographs a Crescent Earth on Its Way to a Comet Rendezvous

Andrew Moseman — Fri, 13 Nov 2009 16:01:36 +0000

This dazzling picture of our planet, all dark but the cerulean sliver of the South Pole, was a long time coming.

Rosetta, a European Space Agency craft, captured this view of the crescent Earth from about 400,000 miles away. The unmanned probe, which is busy chasing comets, was making its third flypast since it was launched in 2004. The close approach gave it a speed boost to send it on its mission to Comet Churyumov-Gerasimenko [Scientific American].

This will be Rosetta’s final visit to its home planet, having already executed a flyby of the asteroid Steins, a gravity assist with Mars, and two previous swoops past the Earth, gathering images all the way. Now it’s off to the comet.

Rosetta is carrying a fridge-sized lab, Philae, that it will send down to the comet. Anchored by tiny hooks, Philae will look for clues about the Solar System’s primal past, exploring a theory that comets are primitive rubble left over from the making of the Solar System [AFP].

While we bid safe travels to Rosetta, it could tell us something about the Earth itself on this final pass. Scientists notice unexpected behavior in spacecraft that make gravitational assists with our planet: Rosetta itself behaved exactly as expected in 2007 flyby but picked up an extra speed boost of 1.8 millimeters per second on its initial maneuver in 2005, leading some mission scientists to speculate that the Earth’s rotation might be distorting space-time more than they thought. “Some studies have looked for answers in new interpretations of current physics. If this proves correct, it would be absolutely groundbreaking news” [MSNBC], says Rosetta flight dynamics specialist Trevor Morley.

Related Content:
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Image: ESA

Scientist Smackdown: Can Nanoparticles Damage Human DNA?

Brett Israel — Mon, 09 Nov 2009 21:52:09 +0000

“Nanoparticles can cause DNA damage across a cellular barrier.” That’s the title of a paper published in Nature Nanotechnology that inspired a number of ominous news headlines (two examples: Nanoparticles ‘can damage DNA‘ and Nanoparticles can damage DNA at a distance: study). The stories that followed basically sang the same tune—that nanoparticles can damage our cells’ genetic material even from a distance (a relatively short distance of four cells away). However, experts are speaking up in response to the media hype, and argue that this study should have never been covered in the news. This particular study has little relevance to human exposure risks, experts say, and it is deeply flawed in other ways [ScienceNOW Daily News]. At least one expert called the study “meaningless,” however other scientists were more diplomatic and have pointed to a number of interesting questions the study raises that are worth pursuing.

In the study, researchers exposed a thin “barrier” of four layers of cancer cells to cobalt-chromium ions or particles. Cells close to the nanoparticles experienced signs of mitochondrial damage. But even cells on the other side of the barrier suffered some DNA damage, the team found, despite the fact that there was no evidence that the metals themselves moved through the cells to the other side of the barrier [ScienceNOW Daily News]. Interesting indeed, but experts are pointing out that this set-up is not entirely relevant to humans, or any living organism for that matter.

The nanoparticles used in the study, cobalt-chromium particles, are not used in any medical treatments, but are used in larger pieces to make replacement hips. Hundreds of thousands of people receive cobalt-chromium implants every year, and there has been no evidence of ill effects reported [New Scientist]. Experts also point out that the experiment exposed cells to the nanoparticles at concentrations that were thousands of times higher than what would ever be seen in the body; remember the maxim that “the dose makes the poison.” Finally, the cells used to construct the barrier are human cancer cells (BeWo cells for the jargon-minded) that have been adapted to life in the petri dish, so they aren’t exactly like cells in the body.

Artificial set up or not, if the nanoparticles didn’t cross the barrier, then how was DNA damaged on the other side? The researchers suggested that the nanoparticles created a cascading chemical change. This is the part that is likely to whet the appetites of other scientists in the field. It looks like the nanoparticles set off a series of signals within the cells of the barrier, that ultimately led to the release of DNA-damaging [molecules] through two specific channels at the edge of the barrier [The Great Beyond]. When the researchers then blocked these channels in a subsequent experiment—poof!—the damage didn’t happen.

The researchers who conducted the experiments have responded to the criticism by saying that they only intended to study how the nanoparticles would interact with the physical barrier; they say they didn’t set out to conduct a realistic assessment of potential dangers posed by the particles. Hopefully, other research groups will set out to do just that. Scientists already suspect that nanoparticles can cause damage in some circumstances, and the need for more research is obvious.

Image: Wikimedia Commons / Nandiyanto

A Gamma Ray Race Through the Fabric of Space-Time Proves Einstein Right

Eliza Strickland — Thu, 29 Oct 2009 20:48:19 +0000

New results are in from the Fermi Space Telescope, which settled into orbit in the summer of 2008, and the findings seem to prove Albert Einstein right once again. Man, that guy was good.

The telescope detected and studied a gamma ray burst, one of the massively bright and powerful explosions that occurs when stars go supernova in distant galaxies. Astronomers were interested in the gamma rays of differing energies and wavelengths that were generated by the explosion, and that raced each other across the universe. After a journey of 7.3 billion light-years, they all arrived within nine-tenths of a second of one another in a detector on NASA’s Fermi Gamma-Ray Space Telescope, at 8:22 p.m., Eastern time, on May 9 [The New York Times].

The researchers were wondering if certain gamma rays with both high energies and short wavelengths would arrive last, at the back of the pack. That would suggest that they had violated one of the principles set out in Einstein’s theory of relativity: that the speed of light is always constant. If researchers could detect a significant lag in some gamma rays, it would also give fresh hope to those ambitious researchers searching for a theory of everything.

At present, two separate theories dominate the world of physics. General relativity explains gravity and the motion of large objects such as planets, stars and galaxies, whereas quantum-mechanics explains the behaviour of very small things such as atoms. Both theories do well at explaining their respective worlds, but they don’t fit together mathematically. The problem is as fundamental as it gets: the two see space and time very differently [Nature News].

Einstein’s general relativity relies on space-time being smooth and continuous, while quantum mechanics suggests that the universe is made up of countless tiny grains of space-time. If the latter model is true, researchers theorized that the lumpy nature of space-time could interfere with the travel of some gamma rays. In simplified terms, that’s because higher energy photons have shorter wavelengths, which makes them more likely to bump into tiny lumps in spacetime and to be slowed by those structures. The slowdown would be tiny, but the lower velocity of high-energy photons could in principle be detectable over a journey of several billion light-years [Science News].

But the study of the Fermi Telescope’s results, published in Nature, declares that since all the gamma rays arrived within nine-tenths of a second apart, they must have all traveled at almost exactly the same speed. That suggests either that space-time is smooth and continuous, as general relativity proposed, or that the grains of space-time are smaller than we ever thought possible, and are having only the most minuscule effect on light waves. Researchers say the grains could theoretically be smaller than one-hundred-thousandth of a trillionth of the size of a proton [Science News].

Physicists working with the Fermi Telescope will keep looking for new evidence. But for now, says study coauthor Peter F. Michelson, “I take it as a confirmation that Einstein is still right” [The New York Times].

Image: NASA. Gamma ray bursts are the universe’s brightest explosions.

Researchers Spot an Ancient Starburst from the Universe’s Dark Ages

Eliza Strickland — Wed, 28 Oct 2009 20:15:18 +0000

Talk about a long trip. An exploding star’s burst of light traveled 13 billion years, from the early days of the universe to the present day, before being detected by astronomers here on Earth. Researchers say this exploding star is the most distant blast ever seen.

The light from the distant explosion, called a gamma-ray burst, first reached Earth on April 23 and was detected by NASA’s Swift satellite. Gamma-ray bursts are thought to be associated with the formation of star-sized black holes as massive stars collapse. Within hours, telescopes around the world were turned on the burst — the most violent explosions in the universe — observing its fading afterglow to glean clues about its source and location [SPACE.com].

As explained in two papers in Nature, the astronomers determined that the explosion happened just 630 million years after the Big Bang during a period of time known as the cosmic dark ages. In that era of primal darkness, the first generation of stars were born. The earliest stars are thought to have been massive, short-lived balls of hydrogen and helium, whereas their offspring incorporated heavier elements formed in the first generation’s explosive demise [Scientific American]. Because the recently viewed blast resembles more recent gamma ray bursts, researchers say the star was probably part of the second or third generations of stars.

Says study coauthor Dale Frail: “The primal cosmic darkness was being pierced by the light of the first stars and the first galaxies were beginning to form. The star that exploded in this event was a member of one of these earliest generations of stars” [SPACE.com]. Researchers plan to train the Hubble Space Telescope on the ancient galaxy where the star exploded in an attempt to learn more about the universe’s first stars.

Image: NASA/Swift/Stefan Immler

A Major Quake Could Release Plutonium From Los Alamos Lab

Brett Israel — Wed, 28 Oct 2009 18:20:26 +0000

Federal experts believe that a major earthquake could trigger fires at Los Alamos National Laboratory, releasing radioactive materials and endangering lives. The rupture of a seismic fault that runs underneath the lab would shake the ground more than scientists previously thought, according to a new report (PDF). A natural disaster here would be bad news, since the lab, just west of Santa Fe, is the main plutonium factory in the United States, believed to hold thousands of pounds of plutonium for use in nuclear weapons (the actual amount is classified).

Researchers study plutonium inside glove boxes—a Hollywood movie staple, consisting of a sealed enclosure with gloves so that someone outside the box can work on dangerous materials inside. A major earthquake would shake the ground enough to topple the glove boxes, says the new study. Some glove boxes are enormous and even contain furnaces to cast and mold plutonium. If one of these were to crash, the resulting fire would be uncontrollable and would create a vaporized plutonium cloud that could drift outside of the lab, says the safety report. In a worst-case scenario, a fire could release so much airborne plutonium that a person on the boundary of the lab would get a dose of radiation—potentially many thousands of times greater than a chest X-ray—that could be fatal in weeks, according to individuals knowledgeable about the study [Los Angeles Times].

The amount of vaporized plutonium could potentially be as much as 100 times more than the level allowed by the Department of Energy. Los Alamos responded to the report by saying they have taken many actions in the past year to increase fire safety including repacking plutonium into containers that would survive the accident. The lab also installed ventilation filters that perform at higher temperatures, improved the fire suppression system, implemented new controls for combustibles, added fire extinguishers to critical areas and developed plans to support firefighter response [AP].

The warning was delivered by Defense Nuclear Facilities Safety Board, an auditing agency that oversees federal nuclear programs; the board urged Energy Secretary Stephen Chu to act quickly to improve safety at Los Alamos. The laboratory will present a formal response to the report later this week.

Image: Los Alamos National Laboratory

What Dangers Lurk in WWII-Era Nuclear Dumps?

Eliza Strickland — Mon, 26 Oct 2009 17:27:40 +0000

Here’s one direct and obvious effect of the economic stimulus package passed in February: The toxic sites where scientists ushered in the nuclear age are getting cleaned up. In Los Alamos, New Mexico, a dump that contains refuse of the Manhattan Project and that was sealed up decades ago is finally being explored, thanks to $212 million from the American Recovery and Reinvestment Act.

But experts aren’t sure what they’ll find inside the dump. At the very least, there is probably a truck down there that was contaminated in 1945 at the Trinity test site, where the world’s first nuclear explosion seared the sky and melted the desert sand 200 miles south of here during World War II [The New York Times]. It may also contain explosive chemicals that could have become more dangerous over the years of burial.

While the Los Alamos dump was alone on a mesa when it was established in 1944, the town has since grown up around it. Today several businesses are across the street from the site, so experts took extra precautions before starting the remediation effort. The team members pored over wartime classified documents and interviewed old-timers to learn what materials might have found their way into the dump, and took soil samples to test their estimates of how much plutonium might be buried there. They debriefed a laboratory worker who, as a young man, once fell into it [The New York Times].

Stimulus money has also gone to other facilities that worked on nuclear weapons. About $1.9 billion has gone to the Hanford site in Washington, where an earlier stage of the cleanup unearthed a metal safe with a glass jug inside. Inside that jug was plutonium left over from the first batch of weapons-grade plutonium ever made. Another batch of Hanford plutonium was used in the nuclear bomb that fell on the Japanese city of Nagasaki. Another $1.6 billion has been dedicated to cleaning up the Savannah River site in South Carolina, where nuclear materials were processed in the 1950s.

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Image: Department of Energy. The Trinity test was the first test of a nuclear weapon.

Stephen Hawking’s Old Job Goes to a String Theory Pioneer

Eliza Strickland — Wed, 21 Oct 2009 18:04:13 +0000

At the University of Cambridge it’s out with black holes, in with tiny vibrating strings of energy. The prestigious professorship that was most recently held by Stephen Hawking, the physicist whose great contributions to the field include new models of black holes, has been given to the string theory luminary Michael Green.

The Lucasian Professorship was established in 1663 and previous holders have included Isaac Newton [BBC News]; it’s considered one of the most prestigious academic posts in the world. Hawking held the job for 30 years, but stepped down in September following his 67th birthday, in accordance with a university rule.

Green is one of the founders of string theory, which many physicists believe paves the way to understanding all of nature’s forces, including electromagnetism, the strong force that holds atomic nuclei together, the weak force that governs certain forms of radiation, and gravity that keeps our feet on the ground and the Earth in orbit around the Sun [The Guardian]. Its goal is to unify the two fundamental physics theories of the 20th century: quantum mechanics, which governs the behavior of subatomic particles, and Einstein’s cosmological theory of general relativity.

String theory, which is formulated in ten dimensions with the extra dimensions ‘compactified’ at very high energy, has met with many successes over the years. It has, for example, been shown to contain all the known particles of the so-called standard model of particle physics [Cambridge Network].

Image: University of Cambridge

Scientists Create “Magnetricity”—Magnetic Charge That Flows Like Electricity

Eliza Strickland — Thu, 15 Oct 2009 17:41:49 +0000

Magnets may have seemed simple when you learned about them in elementary school, but physicists are coaxing some very odd behaviors out of magnetic materials these days. In the latest new development, scientists created the magnetic equivalent of electricity and named the phenomenon “magnetricity.” In the same way that electrically charged particles flow to create an electric current, individual north and south magnetic poles have been observed flowing along to generate a magnetic current.

The basis of the experiment was a refutation of a rule of magnetism observed in our day-to-day lives: No matter how many times you divide a magnet, the resulting fragments will always have both north and south poles. But more than 70 years ago, physicist Paul Dirac theorized that elementary particles should exist that have only a north or south pole, and dubbed these theoretical particles magnetic monopoles. Last month, researchers got closer to spotting a monopole than ever before, when they created ripples that had the same magnetic properties as monopoles.

The new study, published in Nature, describes the phenomenon in a strange, crystalline material known as spin ice. These crystals are made up of pyramids of charged atoms, or ions, arranged in such a way that when cooled to exceptionally low temperatures, the materials show tiny, discrete packets of magnetic charge. Now one of those teams has gone on to show that these “quasi-particles” of magnetic charge can move together, forming a magnetic current just like the electric current formed by moving electrons [BBC News].

To study the phenomenon in greater detail, the research team injected muons – short-lived cousins of electrons – into the spin ice. When the muons decayed, they emitted positrons in directions influenced by the magnetic field inside the spin ice. This revealed that the monopoles were not only present but were moving [New Scientist]. The ripples of distinct north or south charges moved about at random until a magnetic field was applied, which caused the charges to flow through the crystal as a current.

This may seem like fairly abstract research, but physicist Steven Bramwell swears that it could have practical applications–they’ll just be a ways down the road. Data is stored on computer hard discs by magnetising their surfaces in patterns that represent 1s and 0s. Bramwell speculates that monopoles could one day be used as a much more compact form of memory than anything available today, given that the monopoles are only about the size of an atom. “It is in the early stages, but who knows what the applications of magnetricity could be in 100 years time,” he says [New Scientist].

Image: ISIS. Atom-sized north and south poles in spin ice drift in opposite directions when a magnetic field is applied.

How to Create a Black Hole on a Lab Bench

Eliza Strickland — Wed, 14 Oct 2009 22:58:18 +0000

In a lab in Nanjing, China, two researchers are mucking about with what could be called the world’s first artificial black hole–but there’s no reason for alarm. The researchers, Qiang Cheng and Tie Jun Cui, haven’t created a doomsday device, but rather a nifty experiment that harnesses the strange properties of metamaterials. Physicists have already learned how to steer light around an object within a metamaterial to create an invisibility cloak…. Now Qiang and Tie have created a metamaterial that distorts space so severely that light entering it (in this case microwaves) cannot escape [Technology Review].

The lab experiment simulates a cosmological black hole, where the intense gravity curves space-time, sucking in any matter or radiation that gets too close. Not even light can escape a black hole (hence the name). The researchers couldn’t duplicate the intense gravity, but they could build a metamaterial with a physical structure that would make light curve into its central core, never to return. The device they built works only with microwaves so far, but the researchers say a visible light black hole is the next step.

The device consists of 60 layers of circuit board arranged in concentric rings. The layers are coated in copper and etched with intricate patterns that interact with light waves at microwave frequency. “When the incident electromagnetic wave hits the device, the wave will be trapped and guided in the shell region towards the core of the black hole, and will then be absorbed by the core,” says Cui. “The wave will not come out from the black hole.” In their device, the core converts the absorbed light into heat [New Scientist]. The research paper, which has been posted on the preprint server arXiv but hasn’t yet been published, notes that the scientists measured microwaves going in, and found none coming out.

Making a similar device that captures visible light will be quite a challenge, as visible light has a wavelength orders of magnitude smaller than that of microwave radiation. This will require the etched structures to be correspondingly smaller. Cui is confident that they can do it. “I expect that our demonstration of the optical black hole will be available by the end of 2009,” he says [New Scientist].

Images: Qiang Cheng and Tie Jun Cui

Pick a Number. Now, a Brain Scan Will Reveal What It Is.

Brett Israel — Mon, 28 Sep 2009 19:47:40 +0000

Once again, scientists are trying to read your mind. Specifically, they are using fMRI (functional magnetic resonance imaging) to see what areas of the brain people use to process numbers, and even to determine what number a person just viewed.

Test subjects were shown images with either an amount of something—in this case a bunch of dots—or a numeral like 2, 4, or 6. Scientists suspected that our brains use overlapping areas to process quantities and their symbolic representations, however the findings suggest that people process the fundamental idea of a quantity differently from the way they process a symbol representing that quantity [Science News]. When a test subject looked at two dots and later at the number 2, different areas of the brain were activated, researchers report in Current Biology.

Scientists already knew that the the frontal and parietal lobes of the brain are involved in number processing. Monitoring those areas, researchers saw distinct activity patterns associated with specific numerals and dot quantities, and used the info to determine what number the test subjects had just seen.

When it came to small numbers of dots, the researchers found that brain activity patterns changed gradually in a way that reflected the ordered nature of the numbers. For example, one might be able to conclude that the pattern for six is between that for five and seven. In the case of the numerals, the researchers could not detect this same gradual change. This suggests their methods simply might not be sensitive enough to detect this progression yet, or that these symbols are in fact coded as more precise, discrete entities in the brain [LiveScience].

Image: Current Biology / Eger, et al.

How to Make Water Drops Bounce Off Each Other Like Beach Balls

Eliza Strickland — Thu, 17 Sep 2009 14:02:33 +0000

Physicists have found a way to tweak a basic law of nature, and have reversed the rule that opposites–as in oppositely charged droplets of liquid–attract. Typically, when a drop of liquid with a positive charge gets near to another drop with a negative charge, the two come together and merge into a larger whole. But researchers discovered that in a strong electric field with two highly charged droplets, the drops bounce off each other instead.

In the study, published in Nature, researchers used high-speed video to find out what was happening. Drops of liquid usually form tight spheres, but as two electrically charged droplets come close to each other, the spheres begin to warp — and at very short distances, a small bridge of fluid forms between the drops. When the electrical charge is low, that bridge grows until the drops merge together, but when the charge is high, something else happens: the bridge allows the droplets to exchange their charge and then snaps. The water flows back into the bubbles, and by the time the two drops collide, they are back in their spherical shape. Rather than merging, their surface tension causes them to bounce off one another like beach balls [Nature].

The work may sound more like a fun lab trick than vitally important science, but researcher William Ristenpart explains that the findings have implications for many high-tech industries that use electric fields to manipulate tiny water drops. For example, the discovery probably explains why the petroleum industry has not been able to achieve greater efficiencies in the electrostatic removal of water from crude oil, Ristenpart says, a process that has been used for nearly a century, though he adds that the process is extremely difficult to observe because of the opaqueness of the oil [ScienceNOW Daily News].

Image: W.D.Ristenpart and B.Hamlin, U.C.Davis. The top sequence shows the normal action of a drop, while the lower sequence shows the drop bouncing away.

Forget Schrodinger’s Cat. Could We Make Schrodinger’s Virus?

Eliza Strickland — Tue, 15 Sep 2009 18:53:55 +0000

Schrödinger’s Cat may be the most famous thought experiment of all time, but due to its quantum trickiness it must remain in the realm of the hypothetical for the time being. However, researchers suggest they might just be able to pull off a similar, smaller-scale experiment they call Schrödinger’s virus.

The physicist Erwin Schrödinger came up the the feline thought experiment in the 1930s, presenting it as a caution against applying quantum rules to the real, ‘classical’ world…. At its most fundamental level, quantum mechanics says that particles can only exist in discrete states. For example, researchers can measure the direction a particle spins as either ‘up’ or ‘down’, but nothing in between. Yet, as long as no one is looking, the particle exists in a combination of both states simultaneously, a strange blend known as a superposition [Nature News].

Schrödinger proposed an experiment where a cat would be put in box containing a vial of poison gas. A hammer would be suspended ready to smash down on the vial if triggered by the decay of a single atom of radioactive material. If no one looked inside the box, Schrödinger said, the radioactive atom would be in a superposition–both intact and decayed–and therefore the cat would exist in two states as well, being simultaneously alive and dead.

To take a step towards this logical impossibility, researchers propose in a paper posted on the arXiv pre-print server that they start with a much smaller living organism, a virus–although other researchers point out that there is still debate over whether viruses are truly alive. Still, the researchers say that since they think they’ve figured out a way to conduct an experiment putting a single virus in a superposition, it may as well be tried.

The proposed experiment would involve trapping a single virus in a vacuum chamber, and then gradually cooling it and slowing it down until it rests, motionless, in its lowest possible energy state. Finally a single photon, a light particle, would be beamed into the chamber, and as long as nobody peeked inside the chamber the virus would be placed in a superposition of two states: both moving and not.

Researcher Oriol Romero-Isart, one of paper’s coauthors, say the experiment would only work if the virus has certain properties: if it’s dielectric (meaning it doesn’t conduct electricity), can survive the vacuum and appears transparent to laser light, which would otherwise rip it apart. As luck would have it, Romero-Isart and co say that several viruses fit the bill. The common flu virus is known to be able to survive in a vacuum, seems to have the required dielectric properties and may well be transparent to a careful choice of laser light. The tobacco mosaic virus, to all intents and purposes a dielectric rod, looks like another good candidate [Technology Review].

Some experts say the experiment may have limited use. Physicist Martin Plenio (who’s not involved in the proposed research) says there’s no reason to think that a virus will behave differently than an inorganic molecule, but he still thinks that testing relatively large objects, whether viruses or molecules, could prove interesting. According to quantum mechanics, it should be possible for macroscopic objects like cars and people to enter superpositions, but that never appears to happen. Studying relatively large objects, says Plenio, may help physicists learn where the quantum world ends and the our macroscopic world begins [Nature News].

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Image: Wikimedia Commons

Physicists After the Elusive Magnetic Monopole Spot a Look-Alike

Eliza Strickland — Thu, 10 Sep 2009 16:09:19 +0000

Physicists can come off like monster hunters sometimes–their theories predict that a rare beast lurks in the atomic-scale underbrush, so they forge on against all odds, determined to catch a glimpse of their quarry. The latest target is the magnetic monopole, and researchers say they’ve come closer than ever before to spotting it.

Every magnet has a north and a south pole; if you break a magnet into hundreds of pieces, each fragment will also have a north and a south pole of its own. But researchers think that magnetic monopoles exist–particles with only a north or south pole–and there are several reasons physicists would like to see them. In 1931, famed British theorist Paul Dirac argued that the existence of monopoles would explain the quantization of electric charge: the fact that every electron has exactly the same charge and exactly the opposite charge of every proton [ScienceNOW Daily News].

Scientists have scoured the world and the cosmos looking for such particles, says Jonathan Morris, coauthor of one of the two new studies published in Science. “People have been looking for monopoles in cosmic rays and particle accelerators — even Moon rocks” [Nature News], he says. And while the two research groups didn’t quite find the elusive particles, they did detect ripples in strange materials known as spin ices, and found that the ripples have the same magnetic properties as monopoles.

The two groups both used spin ices (one group used holmium titanate and the other used dysprosium titanate), which are man-made solid materials in which the magnetic ions line up like the hydrogen ions in water ice. The magnetic ions sit at the tips of four-sided pyramids or tetrahedra connected corner to corner…. At temperatures near absolute zero, they should organize themselves by a simple rule: In each tetrahedron, two ions point their north poles inward toward the center and two point outward [ScienceNOW Daily News]. But when researchers heated the materials slightly, the tidy magnetic properties of the spin ice was disrupted.

The heating caused tiny flaws in which one ion flipped, leaving its tetrahedron with three ions pointing their north poles inward; that meant the adjacent tetrahedron had only one ion pointing its north poles inward. These lopsided tetrahedrons act, respectively, like north and south magnetic poles. One imbalanced tetrahedron affects another, and the imbalance can flow through the material. These ripples create concentrations of either north or south poles, which amounts, essentially, to magnetic monopoles.

But to physicists like Kimball Milton, the experiments didn’t come close to achieving the ultimate goal of detecting a monopole particle. “I might object to [the researchers] saying ‘genuine magnetic monopoles’, because when you say genuine, that implies to me it’s a point particle, and it’s not,” Milton says. “It’s an effective excitation that at some level looks like a monopole, but it’s not really fundamentally a monopole” [Scientific American].

Looks like there are plenty more monopole hunting expeditions in our future.

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Image: T. Fennell, et al. / Science

Researchers Capture the First-Ever Image of a Single Molecule

Eliza Strickland — Mon, 31 Aug 2009 21:47:23 +0000

With a lot of skillful maneuverings, a team of researchers have finally found a way to image a molecule. The portrait of pentacene, an organic molecule consisting of five benzene rings, shows off the chemical bonds between the carbon and hydrogen atoms.

It may seem a somewhat surprising first, since atoms have been imaged for decades. The earliest pictures of individual atoms were captured in the 1970s by blasting a target – typically a chunk of metal – with a beam of electrons, a technique known as transmission electron microscopy (TEM)…. But strange though it might seem, imaging larger molecules at the same level of detail has not been possible – atoms are robust enough to withstand existing tools, but the structures of molecules are not [New Scientist].

In the new study, published in Science, researchers used an atomic force microscope to image the molecule in unprecedented resolution. The measurement requires extremes of precision. In order to avoid the effects of stray gas molecules bounding around, or the general atomic-scale jiggling that room-temperature objects experience, the whole setup has to be kept under high vacuum and at blisteringly cold temperatures [BBC News]; 5 Kelvin, to be exact. Rather than relying on an optical system to produce pictures, atomic force microscopes use a probe that narrows to an atomic-scale tip, and measures the forces of attraction between the tip and the molecule’s components.

Lead researcher Leo Gross was able to get the shot of pentacene because he stuck a molecule of carbon monoxide (CO) on the tip of the probe. Previously, there have been problems with the tips accidentally sticking to the molecules, and dragging them around the surface during the imaging process. ‘The CO doesn’t bond to the pentacene molecule,’ Gross says, and this means the tip can get very close to the molecule and therefore provide a better image [Chemistry World].

Gross hopes his technique of imaging molecules will help in the nascent field of “molecular electronics”, a potential future for electronics in which individual molecules serve as switches and transistors [BBC News]. In June, Gross released another study showing that atomic force microscopy could image the amount of charge on single atoms. “Now we would like to combine these two works, to observe the transport of charge through molecules on the single electron scale” [Chemistry World], he says.

Image: Science / AAAS