A Possible Victory for Einstein

So it turns out that Einstein may not have been wrong about the universal speed limit. Not only is special relativity safe, it provides an explanation for those faster-than-light neutrinos. They’re not breaking the light-speed barrier; they just appear to be, thanks to the relativistic motion of the clocks checking their speed.

As we all remember, a few weeks ago some scientists at CERN set the physics world on fire when they shared data showing neutrinos were moving faster than light. Specifically, they were showing up at a distant neutrino detector about 60 nanoseconds faster than the time in which light would make the same trip. But the rules of physics said this could not be. 

The Oscillation Project with Emulsion-tRacking Apparatus team (which was not looking for this result, by the way) calibrated their clocks, measured their distances and crunched their numbers in search of an explanation. 

Flummoxed, they dumped their findings on the larger physics community, which proceeded to eviscerate the experiment. In the three weeks since, almost 100 papers have shown up on the preprint server arXiv trying to make sense of it all. Physicists have blamed everything from poor geodesy to ill-timed clocks, and other particle physics observatories are hard at work trying to replicate the results.

Now a Dutch physicist says it’s really very simple — the OPERA team overlooked the relativistic motion of their clocks. Technology Review's arXiv blog highlights the paper here.

OPERA was studying neutrino oscillation, in which these ghostly particles switch from one type to another. They were firing off muon neutrinos from a neutrino beam at CERN and sending them to Gran Sasso, Italy, where researchers counted how many of them had become tau neutrinos. Along with careful Earth-measuring, this experiment required super-precise synchronization of clocks at the two locations. The team did this with GPS satellites, which broadcast a time signal as they orbit about 12,500 miles above the Earth. The OPERA team had to calculate how long it takes for one of these time signals to reach the Earth. But they did not account for the clocks’ relativistic motion, according to physicist Ronald van Elburg at the University of Groningen in the Netherlands.

The radio signals travel from the satellites at light speed, which has nothing to do with the satellites’ speed. This is one of the central tenets of special relativity: “Light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body,” as Einstein put it himself.

But because the satellites are moving, from their point of view, the positions of the neutrinos and the detector are changing. The neutrinos are moving toward the detector, and the detector appears to be moving toward the neutrino source. So the distance between the origin and destination appears to be shorter than it would if it were being observed on the ground.

“Consequently, in this reference frame the distance traveled by the [particles] is shorter than the distance separating the source and detector,” van Elburg writes. This phenomenon is overlooked because the OPERA team thinks of the clocks as on the ground — which they are, physically — and not in orbit, which is where their synchronizing reference point is located.

Using the altitude, orbital period, inclination to the equator and other metrics, van Elburg calculates the error rate: “The observed time-of-flight should be about 32 ns shorter than the time-of-flight using a baseline bound clock,” he writes. This is done at both clock locations, so double that, and you get an early-arrival time of 64 nanoseconds. That pretty much accounts for the OPERA anomaly. 

“This paper shows that Coordinated Universal Time (UTC) happens to be less universal than the name suggests, and that we have to take in to account how our clocks are moving,” van Elburg writes.

Of course, his paper has not yet been published, and is subject to the same scrutiny and peer review as the OPERA folks, so we can’t accept van Elburg’s theory just yet. But it’s certainly a handy explanation. And it’s a lovely piece of irony, too — not only was Einstein’s special theory of relativity right all along, it even provides a reason why.

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Particles Faster Than Speed Of Light At CERN

Enormous underground detectors are needed to catch neutrinos, that are so elusive as to be dubbed "ghost particles".

A meeting at Cern, the world's largest physics lab, has addressed results that suggest subatomic particles have gone faster than the speed of light. 

The team presented its work so other scientists can determine if the approach contains any mistakes.

If it does not, one of the pillars of modern science will come tumbling down.

Antonio Ereditato added "words of caution" to his Cern presentation because of the "potentially great impact on physics" of the result.

The speed of light is widely held to be the Universe's ultimate speed limit, and much of modern physics - as laid out in part by Albert Einstein in his theory of special relativity - depends on the idea that nothing can exceed it.

Thousands of experiments have been undertaken to measure it ever more precisely, and no result has ever spotted a particle breaking the limit.

"We tried to find all possible explanations for this," the report's author Antonio Ereditato of the Opera collaboration told BBC News on Thursday evening.

"We wanted to find a mistake - trivial mistakes, more complicated mistakes, or nasty effects - and we didn't.

"When you don't find anything, then you say 'well, now I'm forced to go out and ask the community to scrutinise this'."

Friday's meeting was designed to begin this process, with hopes that other scientists will find inconsistencies in the measurements and, hopefully, repeat the experiment elsewhere.

"Despite the large [statistical] significance of this measurement that you have seen and the stability of the analysis, since it has a potentially great impact on physics, this motivates the continuation of our studies in order to find still-unknown systematic effects," Dr Ereditato told the meeting.

"We look forward to independent measurement from other experiments."

Neutrinos come in a number of types, and have recently been seen to switch spontaneously from one type to another.

The Cern team prepares a beam of just one type, muon neutrinos, and sends them through the Earth to an underground laboratory at Gran Sasso in Italy to see how many show up as a different type, tau neutrinos.

In the course of doing the experiments, the researchers noticed that the particles showed up 60 billionths of a second earlier than they would have done if they had travelled at the speed of light.

This is a tiny fractional change - just 20 parts in a million - but one that occurs consistently.

The team measured the travel times of neutrino bunches some 16,000 times, and have reached a level of statistical significance that in scientific circles would count as a formal discovery. 

But the group understands that what are known as "systematic errors" could easily make an erroneous result look like a breaking of the ultimate speed limit.

That has motivated them to publish their measurements.

"My dream would be that another, independent experiment finds the same thing - then I would be relieved," Dr Ereditato told BBC News.

But for now, he explained, "we are not claiming things, we want just to be helped by the community in understanding our crazy result - because it is crazy".

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Earth-Generated Panspermia

Jupiter's Moon Europa A new simulation found that high-velocity particles ejected from Earth could make their way to the Jupiter system, where they could conceivably land on a moon like Ganymede or Europa, shown here. Europa is thought to harbor a massive ocean.

Proponents of panspermia theory say life on Earth came from elsewhere, hitching a ride on rocks sheared from other worlds or from migratory asteroids. But what if life did originate here and then it left, hitching a ride on Earth-departed rocks? Earth could seed other worlds, instead of the other way around. A new analysis says the rocks could conceivably make it as far as Jupiter.

 

Scientists have found several meteorites that originated on Mars or the moon, after being ejected in asteroid collisions, forcefully thrown into space and finally arriving on Earth. It makes sense that the opposite could be true, and that after mega-collisions, some pieces of Earth could be thrown toward Mars or Venus.

But most simulations suggest very few Earth pieces would reach the fourth planet, because they would have a hard time overcoming the gravitational pull of both Earth and the sun. Lots of the ejected particles would actually wind up back on Earth, according to previous studies. Some scientists have even suggested these refugee particles would “re-seed” their home planet.

Now researchers in Mexico have a new simulation, and they say plenty of Earth bits would indeed make it to Mars — and beyond, all the way to the Jovian system. Mauricio Reyes-Ruiz and colleagues at the Universidad Nacional Autonoma de Mexico ran computer simulations of 10,242 test particles, following their predicted paths for 30,000 years. That’s about as long as scientists think life could survive in space, the authors note.

They ran simulations at five different ejection velocities, from 6.97 miles per second to 10.2 miles per second. They found that at faster velocities, particles are more likely to reach Jupiter than Mars, because of their great speed relative to Mars’ low gravitational pull. The particles also reach Jupiter more quickly, with half making the trip in 10,000 years, the authors write. In one simulation, just one particle reaches Mars, and it takes between 25,000 and 30,000 years to get there.

Even more bizarre, many particles end up traveling past 40 AU, which the authors describe as leaving the solar system. 

This is all theoretical, of course — the ejection velocity and the particles’ trajectory would be determined by variables like the size and velocity of the incoming object, not to mention the collision location relative to the spin of the Earth. But it’s an interesting concept — as KFC points out over at Technology Review, if life persists in space longer than astrobiologists think, life from Earth could still be speeding toward distant worlds.

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Dust Level High

There is twice as much desert dust in the atmosphere now than a century ago. Particles of dust in the air affect climate and ocean ecology. A better understanding of changing dust levels should help scientists make more accurate climate predictions. 

The amount of dust in the atmosphere has doubled over most of the planet since the last century, finds a new study.

As wind blows through the world's deserts, it whisks dust up into the air and down into the oceans and can significantly affect climate and the environment in all sorts of ways. 

Understanding the changing patterns of dirt particles in the atmosphere could help scientists improve the accuracy of climate predictions. Tracing swirls of dust to their roots could also lead to better land management practices that might mitigate the flow of dust from Earth to sky and sea.

But first, researchers need to figure out why dust levels are rising in the first place. 

"We don't know," said Natalie Mahowald, an atmospheric scientist at Cornell University in Ithaca, N.Y. "It's probably a combination of agriculture and pasture-usage as well as climate change because a lot of regions are getting drier, and that would increase desert dust."

"We put big uncertainty bars on everything," she added. "We need more data."

Climate researchers have spent a lot of time worrying about the effects of particles that human actions release into the atmosphere. Known as anthropomorphic aerosols, these include sulfates from coal-fired power plants and nitrogen oxides from automobile exhaust. 

Mahowald is more interested in desert dust, which can also affect climate in a number of ways. For one thing, particles of soil that are suspended in the air alter the way the atmosphere absorbs and reflects energy from the sun. Dust also changes the properties of clouds, which play a big role in climate patterns. Overall, rising levels of dust tend to cool the atmosphere down.

Dust also affects the chemistry of the oceans. That's because dust contains iron, which boosts growth of plankton, allowing the oceans to pull a little more carbon out of the air. 

To piece together a history of Earth's blowing dust, Mahowald and colleagues compiled a wealth of published data, which included analyses of layered ice cores and sediment samples taken from more than a dozen sites around the world. Most of these cores held specks of dust that had blown in from somewhere else. 

In ice cores from Antarctica, for example, scientists identified soil from South America. Lake sediments in Colorado's San Juan Mountains contained soil particles originally from the Mojave Desert in California, 1,000 kilometers (600 miles) away. Each layer was dated so the researchers could tell how the levels of blowing dust changed over time. 

For the 100-year span from about 1900 to 2000, levels of dust fluctuated quite a bit and patterns differed in different regions, the researchers reported in the journal Atmospheric Chemistry and Physics. Overall, though, levels of dust around the globe doubled everywhere except above North America, where levels dropped a little bit. 

By comparing dusty periods with periods that weren't so dusty, the researchers were able to show that dusty skies lead to lower temperatures -- masking some of the warming effects of greenhouse gasses. As dust accumulates in the air, it also affects clouds enough to move storms away from desert areas, possibly propelling droughts that, in turn, lead to even more dust. 

In the oceans, dust boosts productivity and sucks up more carbon from the air, which can also cool the climate. But that may be offset by erosion and the loss of plant cover on land.

In satellite images of Earth, you can see three obvious colors, said Joseph Prospero, an atmospheric scientist at the University of Miami in Florida: The blue of oceans, the white of clouds and the brown of massive desert dust storms. 

Those images, Prospero said, clearly show that dust is a major player that needs to play a more significant role in climate models as one of a multitude of fluctuating and complicated factors. 

"When climate changes, you get a tremendous amount of variability in dust output," he said. "There is a strong possible loop where the climate becomes drier and windier causing more dust, and more dust affects radiation, so it feeds back on climate."

"There is a lot of uncertainty about how that works," he added. "That's why we focus on dust."

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Good Particles In Upper Atmosphere

         

     A study published July 21 in Science and led by Susan Solomon, of the National Oceanographic and Atmospheric Administration (NOAA), presents new evidence that particles located in the upper layer of the atmosphere -- also called the stratosphere -- have played a significant role in cooling the climate in the past decade, despite being at persistently low levels.

                    According to the paper, "The Persistently Variable 'Background' Stratospheric Aerosol Layer and Global Climate Change," stratospheric aerosols, which are small droplets consisting of sulfuric acid and water, have been reflecting some sunlight back into space, which would have otherwise warmed the Earth.


                    "Stratospheric aerosols are a small variable in the climate change equation," said Larry Thomason, a scientist at NASA's Langley Research Center in Hampton, Va and co-author on the paper. "But if you compare the climate system to a balanced scale, it doesn't take much to tip that scale. Stratospheric aerosols have that potential."


  Volcanic plumes modulate the amount of stratospheric aerosols significantly. Even in times when there aren't large eruptions, such as the past decade, these aerosols have remained present, leaving a consistent background level.

                    Thomason and Jean-Paul Vernier, a co-author on the paper and a NASA Post-Doctoral Fellow at Langley, have worked closely with colleagues to build a record of stratospheric aerosol observations with satellite instruments, which have observed the presence of sulfuric acid droplets in the stratosphere. NASA's Stratospheric Aerosol and Gas Experiment (SAGE II) monitored them from 1984 to 2005, and the joint NASA/CNES Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) has been able to estimate the amount of particles in the stratosphere since its launch in 2006. The NASA data was also combined with data from Global Ozone Monitoring by Occultation of Stars (GOMOS), a European Space Agency instrument. These results, which have been reported in the June 30, 2011 issue of Geophysical Research Letters, show that there has been a slow increase of the stratospheric aerosols during the past decade.
            
                      "None of the climate models, including those used by the IPCC [Intergovernmental Panel on Climate Change] incorporate this slow increase," said Vernier. "If you do not include this effect, you are going to miss a significant cooling component during this decade."
                       These stratospheric aerosols that need to be taken into account are heavily influenced by a natural source - volcanic eruptions.

                       When a volcanic plume reaches the stratosphere, it may inject sulfur dioxide. Within a month, the sulfur dioxide transforms into sulfuric acid droplets, which linger in the stratosphere and reflect sunlight. Human activities, such as burning wood and coal, can also increase the amount of sulfate aerosols in the stratosphere; however, human-caused effects are small compared to those of volcanoes.

      "Even in times without major eruptions, the role of the stratosphere's sulfuric aerosol in climate has remained significant. If they are neglected, it can result in overestimates of global warming in coming decades, particularly if these aerosols remain present at current values or increase," said Thomason.

Millions of tons of sulfur dioxide gas from a major volcanic eruption can reach the stratosphere. After converting to sulfuric acid droplets, these aerosols reflect energy coming from the sun, thereby preventing the sun's rays from heating Earth's surface.

                 Vernier explains that the radiative effects of aerosols are noteworthy - about 1/3 that of carbon dioxide over the past decade. The average radiative forcing between 2000 and 2010 by stratospheric aerosols has cooled the Earth down at 0.1 watts per meter squared, while the amount of carbon dioxide emitted in the same decade has warmed the Earth at 0.3 watts per meter squared.
www.nasa.gov


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Posted in: aerosols,earth,particles,stratosphere