Neutrino experiment repeat at Cern finds same result

The team which found that neutrinos may travel faster than light has carried out an improved version of their experiment – and confirmed the result.

Neutrinos travel through 700km of rock before reaching Gran Sasso’s underground laboratories

If confirmed by other experiments, the find could undermine one of the basic principles of modern physics.

Critics of the first report in September had said that the long bunches of neutrinos (tiny particles) used could introduce an error into the test.

The new work used much shorter bunches.

It has been posted to the Arxiv repository and submitted to the Journal of High Energy Physics, but has not yet been reviewed by the scientific community.

The experiments have been carried out by the Opera collaboration – short for Oscillation Project with Emulsion (T)racking Apparatus.

It hinges on sending bunches of neutrinos created at the Cern facility (actually produced as decays within a long bunch of protons produced at Cern) through 730km (454 miles) of rock to a giant detector at the INFN-Gran Sasso laboratory in Italy.

The initial series of experiments, comprising 15,000 separate measurements spread out over three years, found that the neutrinos arrived 60 billionths of a second faster than light would have, travelling unimpeded over the same distance.

The idea that nothing can exceed the speed of light in a vacuum forms a cornerstone in physics – first laid out by James Clerk Maxwell and later incorporated into Albert Einstein’s theory of special relativity.

Timing is everything

Initial analysis of the work by the wider scientific community argued that the relatively long-lasting bunches of neutrinos could introduce a significant error into the measurement.

Those bunches lasted 10 millionths of a second – 160 times longer than the discrepancy the team initially reported in the neutrinos’ travel time.

To address that, scientists at Cern adjusted the way in which the proton beams were produced, resulting in bunches just three billionths of a second long.

When the Opera team ran the improved experiment 20 times, they found almost exactly the same result.

“This is reinforcing the previous finding and ruling out some possible systematic errors which could have in principle been affecting it,” said Antonio Ereditato of the Opera collaboration.

“We didn’t think they were, and now we have the proof,” he told BBC News. “This is reassuring that it’s not the end of the story.”

The first announcement of evidently faster-than-light neutrinos caused a stir worldwide; the Opera collaboration is very aware of its implications if eventually proved correct.

The error in the length of the bunches, however, is just the largest among several potential sources of uncertainty in the measurement, which must all now be addressed in turn; these mostly centre on the precise departure and arrival times of the bunches.

“So far no arguments have been put forward that rule out our effect,” Dr Ereditato said.

“This additional test we made is confirming our original finding, but still we have to be very prudent, still we have to look forward to independent confirmation. But this is a positive result.”

That confirmation may be much longer in coming, as only a few facilities worldwide have the detectors needed to catch the notoriously flighty neutrinos – which interact with matter so rarely as to have earned the nickname “ghost particles”.

Next year, teams working on two other experiments at Gran Sasso experiments – Borexino and Icarus – will begin independent cross-checks of Opera’s results.

The US Minos experiment and Japan’s T2K experiment will also test the observations. It is likely to be several months before they report back.

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Full article and photo: http://www.bbc.co.uk/news/science-environment-15791236

Dutch Scientists Drive Single-Molecule Car

Scientists in the Netherlands have introduced a molecule-sized car. Legroom might be an issue.

Its wheels are comprised of a few atoms each; its motor, a mere jolt of electricity. Scientists in the Netherlands have introduced the world’s smallest car — and it’s only a single molecule long.

It’s certainly no Porsche, but scientists at the University of Groningen in the Netherlands are still excited about their latest achievement: creating a “car” that’s only a billionth of a meter long.

The nanometer-sized vehicle, introduced in the British journal Nature on Wednesday, is comprised of a miniscule frame with four rotary units, each no wider than a few atoms. In fact, the whole construction is 60,000 times thinner than a human hair, according to the AFP news agency.

The research team was able to propel the nanocar six billionths of a meter by firing electrons at it with a tunnelling electron microscope. The “electronic and vibrational excitation” of the jolts changes the way the atoms of the “wheels” interact with those on a copper surface, the reports says, propelling the car forward in a single direction. The only problem, it would seem, is getting all the wheels to turn in the same direction every time.

A Small Future

It might be tough to imagine the use of such a diminutive roadster. But nanotechnology is widely considered one of the most exciting fields of the 21st century, and the researchers view their design as “a starting point for the exploration of more sophisticated molecular mechanical systems with directionally controlled motion.”

Utilizing materials at an atomic or molecular level — “nano” comes from the Greek word for “dwarf” — finds applications in everything from medicine and engineering to consumer products, such as sunscreen, ketchups and even powdered sugar.

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Full article and photo: http://www.spiegel.de/international/zeitgeist/0,1518,796970,00.html

Going round in circles

Cosmology

In contradiction to most cosmologists’ opinions, two scientists have found evidence that the universe may have existed for ever

WHAT happened before the beginning of time is—by definition, it might be thought—metaphysics. At least one physicist, though, thinks there is nothing meta about the question at all. Roger Penrose, of Oxford University, believes that the Big Bang in which the visible universe began was not actually the beginning of everything. It was merely the latest example of a series of such bangs that renew reality when it is getting tired out. More importantly, he thinks that the pre-Big Bang past has left an imprint on the present that can be detected and analysed, and that he and a colleague in Armenia have found it.

The imprint in question is in the cosmic microwave background (CMB). This is a bath of radiation that fills the whole universe. It was frozen in its present form some 300,000 years after the Big Bang, and thus carries information about what the early universe was like. The CMB is almost, but not quite, uniform, and the known irregularities in it are thought to mark the seeds from which galaxies—and therefore stars and planets—grew.

Dr Penrose, though, predicts another form of irregularity—great circles in the sky where the microwave background is slightly more uniform than it should be. These, if they exist, would be fossil traces of black holes from the pre-Big Bang version of reality. And in a paper just published in arXiv.org, an online database, he claims they do indeed exist.

Once upon a time

The Penrose version of cosmology stands in sharp distinction to received wisdom. This is that the universe popped out of nowhere about 13.7 billion years ago in a quantum fluctuation similar to the sort that constantly create short-lived virtual particles in so-called empty space. Before this particular fluctuation could disappear again, though, it underwent a process called inflation that both stabilised it and made it 10⁷⁸ times bigger than it had previously been in a period of 10^-32 seconds. Since then, it has expanded at a more sedate rate and will continue to do so—literally for ever.

Dr Penrose, however, sees inflation as a kludge. The main reason it was dreamed up (by Alan Guth, a cosmologist at the Massachusetts Institute of Technology) was to explain the extraordinary uniformity of the universe. A period of rapid inflation right at the beginning would impose such uniformity by stretching any initial irregularities so thin that they would become invisible.

As kludges go, inflation has been successful. Those of its predictions that have been tested have all been found true. But that does not mean it is right. Dr Penrose’s explanation of the uniformity is that, rather than having been created at the beginning of the universe, it is left over from the tail end of reality’s previous incarnation.

Dr Penrose’s version of events is that the universe did not come into existence at the Big Bang but instead passes through a continuous cycle of aeons. Each aeon starts off with the universe being of zero size and high uniformity. At first the universe becomes less uniform as it evolves and objects form within it. Once enough time has passed, however, all of the matter around will end up being sucked into black holes. As Stephen Hawking has demonstrated, black holes eventually evaporate in a burst of radiation. That process increases uniformity, eventually to the level the universe began with.

Thus far, Dr Penrose’s version of cosmology more or less matches the standard version. At this point, though, he introduces quite a large kludge of his own. This is the idea that when the universe becomes very old and rarefied, the particles within it lose their mass.

That thought is not entirely bonkers. The consensus among physicists is that particles began massless and got their mass subsequently from something known as the Higgs field—the search for which was one reason for building the Large Hadron Collider, a huge and powerful particle accelerator located near Geneva. Mass, then, is not thought an invariable property of matter. So Dr Penrose found himself speculating one day about how a universe in which all particles had lost their mass through some as-yet-undefined process might look. One peculiarity of massless particles is that they have to travel at the speed of light. That (as Einstein showed) means that from the particle’s point of view time stands still and space contracts to nothingness. If all particles in the universe were massless, then, the universe would look to them to be infinitely small. And an infinitely small universe is one that would undergo a Big Bang.

Uncommon sense

It is well known that fundamental physics is full of ideas that defy what humans are pleased to call common sense. Even by those standards, however, Dr Penrose’s ideas are regarded as a little eccentric by his fellow cosmologists. But they do have one virtue that gives them scientific credibility: they make a prediction. Collisions between black holes produce spherical ripples in the fabric of spacetime, in the form of gravitational waves. In the Penrose model of reality these ripples are not abolished by a new Big Bang. Images of black-hole collisions that happened before the new Bang may thus imprint themselves as concentric circular marks in the emerging cosmic microwave background.

The actual search for such cosmic circles has been carried out by Vahe Gurzadyan of the Yerevan Physics Institute in Armenia. Dr Gurzadyan analysed seven years’ worth of data from WMAP, an American satellite whose sole purpose is to measure the CMB, and also looked at data from another CMB observatory, the BOOMERanG balloon experiment in Antarctica. His verdict, arrived at after he scoured over 10,000 points on the microwave maps, is that Dr Penrose’s concentric circles are real. He says he has found a dozen sets of them—one of which is illustrated. (The visible rings in the picture have been drawn on subsequently to show where computer analysis has found circle-defining uniformity.)

This is, of course, but a single result—and supporters of inflation do not propose to give up without a fight. Amir Hajian, a physicist at Princeton, for example, says he is concerned about distortions in the WMAP data caused by the satellite spending more time mapping some parts of the sky than others. Then there is the little matter of how the masslessness comes about.

Dr Guth, meanwhile, claims that a handful of papers are published every year pointing to inconsistencies between the microwave background data and inflation, and that none has withstood the test of time. Moreover, even if the circles do hold up, they may have a cause different from the one proposed by Dr Penrose. Nevertheless, when a strange theory makes a strange prediction and that prediction proves correct, it behoves science to investigate carefully. For if what Dr Penrose and Dr Gurzadyan think they have found is true, then much of what people thought they knew about the universe is false.

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Full article and photo: http://www.economist.com/node/17626874

Stone Power

Q. I’ve heard that if a penny is dropped from the Empire State Building it could kill someone. But what about hail? It’s often much larger and falls from much higher, so why do I never hear about any deaths caused by it?

A. Hail can cause human fatalities, but does not usually do so, according to the National Severe Storms Laboratory of the National Oceanic and Atmospheric Administration.

While one hail event in India in 1988 caused 246 deaths, this was truly exceptional. In the United States, most years see no deaths at all, though one or two are very rarely reported. It has been suggested that one reason for this is that Americans spend less time out in the open than people who live in regions like northern India where hail is a greater risk to human life.

Another important factor is that hail does not fall uninterrupted from the high reaches of the atmosphere, but is tossed up and down by the winds of a thunderstorm, bumping into raindrops and other hailstones, a process that slows the fall. The winds also frequently make the hailstones fall at an angle.

The friction with other precipitation deforms a hailstone from a perfect sphere, making its velocity hard to calculate when it does become heavy enough to fall to earth. One estimate is that a half-inch stone falls about 30 feet a second, while a three-inch stone falls nearly 160 feet a second.

C. Clairbone Ray, New York Times

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Full article and photo: http://www.nytimes.com/2010/10/19/science/19qna.html

Dr Hawking’s bright idea

Mimicking black holes

A long-predicted phenomenon has turned up in an unexpected place

IN 1974 Stephen Hawking, pictured right, had a startling theoretical insight about black holes—those voracious eaters of matter and energy from whose gravitational clutches not even light can escape. He predicted that black holes should not actually be black. Instead, because of the quirks of quantum mechanics, they should glow ever so faintly, like smouldering embers in a dying fire. The implications were huge. By emitting this so-called Hawking radiation, a black hole would gradually lose energy and mass. If it failed to replenish itself it would eventually evaporate completely, like a puddle of water on a hot summer’s day.

Unfortunately for physicists, Dr Hawking also predicted that the typical temperature at which a black hole radiates should be about a billionth of that of the background radiation left over from the Big Bang itself. Proving his theory by observing actual Hawking radiation from a black hole in outer space has therefore remained a practical impossibility.

In a paper just accepted by Physical Review Letters, however, a team of researchers led by Daniele Faccio from the University of Insubria, in Italy, report that they have observed Hawking radiation in the laboratory. They managed this trick not by creating an Earth-gobbling black hole on a benchtop but by firing pulses of laser light into a block of glass. This created a region from which light could not escape (analogous to a black hole) and also its polar opposite, a region which light could not enter. When the team focused a sensitive camera on to the block, they saw the faint glow of Hawking radiation.

Black and light

If a dying star is massive enough, it can collapse to form a region of infinite density, called a singularity. The gravity of such an object is so strong that nothing, not even light itself, can break free if it strays too close. Once something has passed through the so-called event horizon that surrounds this region, it is doomed to a one-way trip.

Dr Hawking’s insight came from considering what happens in the empty space just outside the event horizon. According to quantum mechanics, empty space is anything but empty. Rather, it is a roiling, seething cauldron of evanescent particles. For brief periods of time, these particles pop into existence from pure nothingness, leaving behind holes in the nothingness—or antiparticles, as physicists label them. A short time later, particle and hole recombine, and the nothingness resumes.

If, however, the pair appears on the edge of an event horizon, either particle or hole may wander across the horizon, never to return. Deprived of its partner, the particle (or the hole) has no “choice” but to become real. These particles, the bulk of which are photons (the particles of light), make up Hawking radiation—and because photons and antiphotons are identical, the holes contribute equally. The energy that goes into these now-real photons has to come from somewhere; that somewhere is the black hole itself, which thus gradually shrinks. By linking the disparate fields of gravitational science, quantum mechanics and thermodynamics, Hawking radiation has become a crucial concept in theoretical physics over the past quarter of a century.

In 1981, that concept was extended. William Unruh of the University of British Columbia pointed out that black holes are actually extreme examples of a broader class of physical systems that can form event horizons. Consider a river approaching a waterfall. As the water nears the edge, the current moves faster and faster. In theory, it can move so fast that ripples on the surface are no longer able to escape back upstream. In effect, an event horizon has formed in the river, preventing waves from making their way out. Since then, other researchers have come up with other quotidian examples of event horizons.

Dr Faccio and his team were able to create their version because, as the laser pulse moves through the glass block, it changes the glass’s refractive index (the speed at which light travels through a material). Light in the vicinity of the pulse is slowed more and more when the refractive index changes as the pulse passes by.

To see how the pulse can act like a black hole, imagine that it is sent chasing after a slower, weaker pulse. It will gradually catch up with this slow pulse, reducing the speed of light in the slow pulse’s vicinity. That will slow the slow pulse down still more until eventually it is slowed so much that it is stuck. Essentially, the leading edge of the chasing pulse sucks it in, acting like the event horizon of a black hole.

Now imagine that the chasing pulse is itself being chased, but again by a much weaker pulse. As this third pulse approaches the tail of the second one it will also slow down (because the speed of light in the glass it is passing through has been reduced by the second pulse’s passage). The closer it gets, the slower it travels, and it can never quite catch up. The trailing edge of the second pulse, therefore, also acts as an event horizon. This time, though, it stops things getting in rather than stopping them getting out. It resembles the opposite of a black hole—a white hole, if you like.

In the actual experiment, there were no leading and trailing pulses. Instead, their role was played by evanescent photons continually popping into existence around the strong pulse. As the pulse passed through the glass, its event horizons should have swept some of these photons up, producing Hawking radiation from the partners they left behind.

Sure enough, when Dr Faccio and his team focused a suitable camera on the block and fired 3,600 pulses from their laser, they recorded a faint glow at precisely the range of frequencies which the theory of Hawking radiation predicts. After carefully considering and rejecting other possible sources for this light, they conclude that they have indeed observed Hawking radiation for the first time.

Because of its tabletop nature, other groups will certainly attempt to replicate and extend Dr Faccio’s experiment. Although such studies cannot prove that real black holes radiate and evaporate, they lend strong support to the ideas that went into Dr Hawking’s line of reasoning. Unless a tiny black hole turns up in the collisions of a powerful particle accelerator, that may be the best physicists can hope for. It may even be enough to convince Sweden’s Royal Academy of Science to give Dr Hawking the Nobel prize that many think he deserves, but which a lack of experimental evidence has hitherto caused it to withhold.

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Full article and photo: http://www.economist.com/node/17145159

Ye cannae change the laws of physics

Or can you?

RICHARD FEYNMAN, Nobel laureate and physicist extraordinaire, called it a “magic number” and its value “one of the greatest damn mysteries of physics”. The number he was referring to, which goes by the symbol alpha and the rather more long-winded name of the fine-structure constant, is magic indeed. If it were a mere 4% bigger or smaller than it is, stars would not be able to sustain the nuclear reactions that synthesise carbon and oxygen. One consequence would be that squishy, carbon-based life would not exist.

Why alpha takes on the precise value it has, so delicately fine-tuned for life, is a deep scientific mystery. A new piece of astrophysical research may, however, have uncovered a crucial piece of the puzzle. In a paper just submitted to Physical Review Letters, a team led by John Webb and Julian King from the University of New South Wales in Australia present evidence that the fine-structure constant may not actually be constant after all. Rather, it seems to vary from place to place within the universe. If their results hold up to the scrutiny, and can be replicated, they will have profound implications—for they suggest that the universe stretches far beyond what telescopes can observe, and that the laws of physics vary within it. Instead of the whole universe being fine-tuned for life, then, humanity finds itself in a corner of space where, Goldilocks-like, the values of the fundamental constants happen to be just right for it.

Slightly belying its name, the fine-structure constant is actually a compound of several other physical constants, whose values can be found in any physics textbook. You start with the square of an electron’s charge, divide it by the speed of light and Planck’s constant, then multiply the whole lot by two pi. The point of this convoluted procedure is that this combination of multiplication and division produces a pure, dimensionless number. The units in which the original measurements were made cancel each other out and the result is 1/137.036, regardless of the measuring system you used in the first place.

Despite its convoluted origin, though, alpha has a real meaning. It characterises the strength of the force between electrically charged particles. As such, it governs—among other things—the energy levels of an atom formed from negatively charged electrons and a positive nucleus. When electrons jump between these energy levels, they absorb and emit light of particular frequencies. These frequencies show up as lines (dark for absorption; bright for emission) in a spectrum. When many different energy levels are involved, as they are in the spectrum of a chemically mixed star, the result is a fine, comb-like structure—hence the constant’s name. If it were to take on a different value, the wavelengths of these lines would change. And that is what Dr Webb and Mr King think they have found.

The light in question comes not from individual stars but from quasars. These are extremely luminous (and distant) galaxies whose energy output is powered by massive black holes at their centres. As light from a quasar travels through space, it passes through clouds of gas that imprint absorption lines onto its spectrum. By measuring the wavelengths of a large collection of these absorption lines and subtracting the effects of the expansion of the universe, the team led by Dr Webb and Mr King was able to measure the value of alpha in places billions of light-years away.

Dr Webb first conducted such a study almost a decade ago, using 76 quasars observed with the Keck telescope in Hawaii. He found that, the farther out he looked, the smaller alpha seemed to be. In astronomy, of course, looking farther away means looking further back in time. The data therefore indicated that alpha was around 0.0006% smaller 9 billion years ago than it is now. That may sound trivial. But any detectable deviation from zero would mean that the laws of physics were different there (and then) from those that pertain in the neighbourhood of the Earth.

Such an important result needed independent verification using a different telescope, so in 2004 another group of researchers looked from the European Southern Observatory’s Very Large Telescope (VLT) in Chile. They found no evidence for any variation of alpha. Since then, though, flaws have been discovered in that second analysis, so Dr Webb and his team set out to do their own crosscheck with a sample of 60 quasars observed by the VLT.

What they found shocked them. The further back they looked with the VLT, the larger alpha seemed to be—in seeming contradiction to the result they had obtained with the Keck. They realised, however, that there was a crucial difference between the two telescopes: because they are in different hemispheres, they are pointing in opposite directions. Alpha, therefore, is not changing with time; it is varying through space. When they analysed the data from both telescopes in this way, they found a great arc across the sky. Along this arc, the value of alpha changes smoothly, being smaller in one direction and larger in the other. The researchers calculate that there is less than a 1% chance such an effect could arise at random. Furthermore, six of the quasars were observed with both telescopes, allowing them to get an additional handle on their errors.

If the fine-structure constant really does vary through space, it may provide a way of studying the elusive “higher dimensions” that many theories of reality predict, but which are beyond the reach of particle accelerators on Earth. In these theories, the constants observed in the three-dimensional world are reflections of what happens in higher dimensions. It is natural in these theories for such constants to change their values as the universe expands and evolves.

Unfortunately, their method does not allow the team to tell which of the constants that goes into alpha might be changing. But it suggests that at least one of them is. On the other hand, the small value of the change over a distance of 18 billion light-years suggests the whole universe is vastly bigger than had previously been suspected. A diameter of 18 billion light-years (9 billion in each direction) is a considerable percentage of observable reality. The universe being 13.7 billion years old, 13.7 billion light-years—duly stretched to allow for the expansion of the universe—is the maximum distance it is possible to see in any direction. If the variation Dr Webb and Mr King have found is real, and as gradual as their data suggest, you would have to go a very long way indeed to come to a bit of space where the fine-structure constant was more than 4% different from its value on Earth.

If. Other teams of astronomers are already on the case, and Victor Flambaum, one of Dr Webb’s colleagues at the University of New South Wales, points out in a companion paper that laboratory tests involving atomic clocks only slightly better than those that exist already could provide an independent check. These would vary as the solar system moves through the universe. But if and when such confirmation comes, it will break one of physics’s greatest taboos, the assumption that physical laws are the same everywhere and everywhen. And the fine-structure constant will have shown itself to be more mysterious than even Feynman conceived.
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Full article and photo: http://www.economist.com/node/16930866

Sun storm

Meet the northern lights

THIS PAST week, residents of several US states had a rare opportunity to see the northern lights bathe the sky in their eerie glow of pale green and red. The lights are normally only visible in far northern latitudes, but a surge of activity from the sun pushed them far enough south that there was even a chance we’d get a glimpse in Massachusetts. And fortunately for sky watchers, this may only be the beginning: Scientists say the sun is being roused into a period of high activity, which may bring more displays over the next few years.

The northern lights are a rare visible manifestation of space weather, the currents of matter and energy that roil above the earth’s lower atmosphere. The lights are caused by solar wind — protons and electrons streaming outwards from the sun — which can gust at speeds up to thousands of kilometers per second. When these winds push against the earth’s magnetic field, the result is a geomagnetic storm that appears to us as an aurora — arcs, sheets, or rippled filaments of light. In northern latitudes, this phenomenon is called the aurora borealis, after the Roman goddess of dawn and the Greek word for north wind. The aurora borealis only reaches the Boston area every few years; our last glimpse was in 2005.

The recent storm was created by an enormous blast from the sun called a coronal mass ejection. Although it made for some beautiful displays, it’s by no means the most impressive we’ve seen. In the summer of 1859, a huge solar flare lit up skies across Europe, the United States, and even Japan. A New York Times article from Sept. 2 that year said the northern lights in Boston were “so brilliant that at about one o’clock ordinary print could be read by the light.” That night, two operators of the telegraph line between Boston and Portland conversed for two hours powered solely by current induced by the aurora.

The sun’s cycles of activity last about 11 years on average, and after two quiet years — a longer rest than usual — the sun is stirring back into action. This means more opportunities for watching the dramatic storms it causes. In the meantime, you can see spectacular views of the sun’s activity at NASA’s Solar Dynamics Observatory website. A gallery of images of the recent aurora taken from around the world is on display at spaceweather.com, and devoted sky watchers can also sign up there for “aurora alerts” on their cellphones. Anyone who wants to track space weather conditions, including opportunities to view aurorae, can follow the National Weather Service’s Space Weather Prediction Center (swpc.noaa.gov). Should another chance come, the best way to see the northern lights is to escape city light pollution, ideally by finding a remote spot in the country with unobstructed views of the northern sky.

Courtney Humphries, author of ”Superdove: How the Pigeon Took Manhattan…And the World,” is a regular contributor to Ideas.

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Full article and photo: http://www.boston.com/bostonglobe/ideas/articles/2010/08/08/sun_storm/