falling Archives ⋆ Page 2 of 4 ⋆ Dimensional Bliss

Tag: falling (page 2 of 4)

Study finally answers why it smells so good after it rains

Excerpt from usatoday.comIt turns out tiny bubbles may be to thank for that earthy smell we get after it rains, according to a study from researchers at the Massachusetts Institute of Technology.Youngsoo Joung and Cullen R. Buie used high-speed came...

View Article Here Read More

Top 10 Ridiculously Common Science Myths

November 30, 2014 / Greg Giles / 0 Comments

listverse.com
There is nothing better than a bit of mythbusting (which accounts for the popularity of the television program of the same name), so here we are again, presenting you with a new list of terribly common misconceptions and myths – this time about science.

Evolutionary Improvements

The Myth: Evolution causes something to go from “lower” to “higher”
While it is a fact that natural selection weeds out unhealthy genes from the gene pool, there are many cases where an imperfect organism has survived. Some examples of this are fungi, sharks, crayfish, and mosses – these have all remained essentially the same over a great period of time. These organisms are all sufficiently adapted to their environment to survive without improvement.
Other taxa have changed a lot, but not necessarily for the better. Some creatures have had their environments changed and their adaptations may not be as well suited to their new situation. Fitness is linked to their environment, not to progress.

Humans Pop In Space

The Myth: When exposed to the vacuum of space, the human body pops
This myth is the result of science fiction movies which use it to add excitement or drama to the plot. In fact, a human can survive for 15 – 30 seconds in outer space as long as they breathe out before the exposure (this prevents the lungs from bursting and sending air into the bloodstream). After 15 or so seconds, the lack of oxygen causes unconsciousness which eventually leads to death by asphyxiation.

Brightest Star

The Myth: Polaris is the brightest star in the northern hemisphere night sky
Sirius is actually brighter with a magnitude of ?1.47 compared to Polaris’ 1.97 (the lower the number the brighter the star). The importance of Polaris is that its position in the sky marks North – and for that reason it is also called the “North Star”. Polaris is the brightest star in the constellation Ursa Minor and, interestingly, is only the current North Star as pole stars change over time because stars exhibit a slow continuous drift with respect to the Earth’s axis.

Five Second Rule

The Myth: Food that drops on the floor is safe to eat if you pick it up within five seconds
This is utter bunkum which should be obvious to most readers. If there are germs on the floor and the food lands on them, they will immediately stick to the food. Having said that, eating germs and dirt is not always a bad thing as it helps us to develop a robust immune system. I prefer to have a “how-tasty-is-it” rule: if it is something really tasty, it can sit there for ten minutes for all I care – I will still eat it.

Dark side of the Moon

The Myth: There is a dark side of the moon
Actually – every part of the moon is illuminated at sometime by the sun. This misconception has come about because there is a side of the moon which is never visible to the earth. This is due to tidal locking; this is due to the fact that Earth’s gravitational pull on the moon is so immense that it can only show one face to us. Wikipedia puts it rather smartly thus: “Tidal locking occurs when the gravitational gradient makes one side of an astronomical body always face another; for example, one side of the Earth’s Moon always faces the Earth. A tidally locked body takes just as long to rotate around its own axis as it does to revolve around its partner. This synchronous rotation causes one hemisphere constantly to face the partner body.”

Brain Cells

The Myth: Brain cells can’t regenerate – if you kill a brain cell, it is never replaced
The reason for this myth being so common is that it was believed and taught by the science community for a very long time. But in 1998, scientists at the Sweden and the Salk Institute in La Jolla, California discovered that brain cells in mature humans can regenerate. It had previously been long believed that complex brains would be severely disrupted by new cell growth, but the study found that the memory and learning center of the brain can create new cells – giving hope for an eventual cure for illnesses like Alzheimer’s.

Pennies from Heaven

The Myth: A penny dropped from a very high building can kill a pedestrian below
This myth is so common it has even become a bit of a cliche in movies. The idea is that if you drop a penny from the top of a tall building (such as the Empire State Building) – it will pick up enough speed to kill a person if it lands on them on the ground. But the fact is, the aerodynamics of a penny are not sufficient to make it dangerous. What would happen in reality is that the person who gets hit would feel a sting – but they would certainly survive the impact.

Friction Heat

The Myth: Meteors are heated by friction when entering the atmosphere
When a meteoroid enters the atmosphere of the earth (becoming a meteor), it is actually the speed compressing the air in front of the object that causes it to heat up. It is the pressure on the air that generates a heat intense enough to make the rock so hot that is glows brilliantly for our viewing pleasure (if we are lucky enough to be looking in the sky at the right time). We should also dispel the myth about meteors being hot when they hit the earth – becoming meteorites. Meteorites are almost always cold when they hit – and in fact they are often found covered in frost. This is because they are so cold from their journey through space that the entry heat is not sufficient to do more than burn off the outer layers.

Lightning

The Myth: Lightning never strikes the same place twice
Next time you see lightning strike and you consider running to the spot to protect yourself from the next bolt, remember this item! Lightning does strike the same place twice – in fact it is very common. Lightning obviously favors certain areas such as high trees or buildings. In a large field, the tallest object is likely to be struck multiple times until the lightning moves sufficiently far away to find a new target. The Empire State Building gets struck around 25 times a year.

Gravity in Space

The Myth: There is no gravity in space
In fact, there is gravity in space – a lot of it. The reason that astronauts appear to be weightless because they are orbiting the earth. They are falling towards the earth but moving sufficiently sideways to miss it. So they are basically always falling but never landing. Gravity exists in virtually all areas of space. When a shuttle reaches orbit height (around 250 miles above the earth), gravity is reduced by only 10%.
Inspired by an excellent LiveScience Article. This article is licensed under the GFDL because it contains quotations from Wikipedia.

View Article Here Read More

Rosetta mission: Philae lander bounces twice, lands on side ~ Cliff face blocking solar power

November 13, 2014 / Greg Giles / 0 Comments

How Esa scientists believe Philae has landed on the comet – on its side. Photograph: European Space Agency/Reuters

Excerpt from
theguardian.com

Rosetta mission controllers must decide whether to risk making lander hop from shadow of cliff blocking sunlight to its solar panels.

The robotic lander that touched down on a comet on Wednesday came to rest on its side in the shadow of a cliff, according to the first data beamed home from the probe.

Pictures from cameras on board the European Space Agency’s Philae lander show the machine with one foot in the sky and lodged against a high cliff face that is blocking sunlight to its solar panels.
The precarious resting place means mission controllers are faced with some tough decisions over whether to try and nudge the spacecraft into a sunnier spot. If successful, that would allow Philae to fully recharge its batteries and do more science on the comet, but any sudden move could risk toppling the lander over, or worse, knock it off the comet completely.

The washing machine-sized lander was released by its Rosetta mother ship at 0835am GMT on Wednesday morning and touched down at a perfect spot on the comet’s surface. But when anchoring harpoons failed to fire, the probe bounced back off into space. So weak is the gravitational pull of the comet that Philae soared 1km into the sky and did not come down again until two hours later. “We made quite a leap,” said Stephan Ulamec, the Philae lander manager.

In the time it took the probe to land for the second time, the comet had rotated, bringing more treacherous terrain underneath. The spacecraft bounced a second time and finally came to a standstill on its side at what may be the rim of an enormous crater.

“We bounced twice and stopped in a place we’ve not entirely located,” said Jean-Pierre Bibring, Philae’s lead scientist. Teams of scientists are now trying to work out where the probe is. What mission controllers do know is that they are not where they hoped to be. “We are exactly below a cliff, so we are in a shadow permanently,” Bibring added.

With most of Philae in the dark, the lander will receive only a fraction of the solar energy that Esa had hoped for. The spacecraft needs six or seven hours of sunlight a day but is expected to receive just one and a half. Though it can operate for 60 hours on primary batteries, the probe must then switch to its main batteries which need to be recharged through its solar arrays. If Philae’s batteries run out it will go into a hibernation mode until they have more power.

The spacecraft was designed with landing gear that could hop the probe around, but from its awkward position on its side the option is considered too risky.

Though caught in a tight spot, the Philae lander’s systems appear to be working well. The Rosetta spacecraft picked up the lander’s signal on Thursday morning and received the first images and more instrument data from the surface of the comet.

One of Philae’s major scientific goals is to analyse the comet for organic molecules. To do that, the lander must get samples from the comet into several different instruments, named Ptolemy, Cosac and Civa. There are two ways to do this: sniffing and drilling. Sniffing involves opening the instruments to allow molecules from the surface to drift inside. The instruments are already doing this and returning data.

Panoramic view around the point of Philae's final touchdown on the surface of comet 67P, taken when Rosetta was about 18km from centre of comet. Parts of Philae's landing gear can be seen in this picture. — Panoramic view around the point of Philae’s final touchdown on the surface of comet 67P, taken when Rosetta was about 18km from centre of comet. Parts of Philae’s landing gear can be seen in this picture.Photograph: European Space Agency/AFP/Getty Images

Drilling is much riskier because it could make the lander topple over... Pushing down into the surface will push the lander off again. “We don’t want to start drilling and end the mission,” said Bibring.
But the team has decided to operate another moving instrument, named Mupus, on Thursday evening. This could cause Philae to shift, but calculations show that it would be in a direction that could improve the amount of sunlight falling on the probe. A change in angle of only a few degrees could help. A new panoramic image will be taken after the Mupus deployment to see if there has been any movement.

Meanwhile, the Rosetta orbiter team will continue to try to pinpoint Philae’s position.

View Article Here Read More

Why France has a team of UFO hunters

November 8, 2014 / Greg Giles / 0 Comments

A drawing from the files at the French UFO departmentExcerpt from BBCBy Chris Bockman Thousands of UFO sightings are reported every year but not many countries are willing to spend money investigating them - there is just one dedicated state-run tea...

View Article Here Read More

First legal pot, now Colorado launches new voting experiment

November 1, 2014 / Greg Giles / 0 Comments

Excerpt from nypost.com

As Colorado goes Election Night, so goes the nation — maybe.
The Centennial State is clearly a barometer of President Obama’s falling popularity.

The man who began his meteoric rise as the Democratic presidential nominee in Denver’s stadium in 2008 has lost much of his luster with Colorado voters and appears to be bringing down other Democrats with him.

Polls show Republican Cory Gardner ahead by seven points in his race to unseat incumbent Democratic Sen. Mark Udall, and GOP gubernatorial candidate Bob Beauprez is neck and neck with sitting Gov. John HIckenlooper.

But before Republicans pop the champagne corks, it’s worth considering the big wild card in this election.

Like the rest of Colorado’s roughly 3 million registered voters, I received my ballot in the mail about two weeks ago. This year will be the first that all Colorado voters received mail ballots, even without requesting them.

The potential for thousands more voters to cast ballots in what is usually a low-turnout midterm election could easily confound pollsters and politicos.

Conventional wisdom is that higher turnout favors Democrats — and the odds of higher turnout helping Dems in Colorado seem somewhat greater, given the demographics of the state.
Some 14 percent of eligible voters in Colorado are Hispanic. Obama improved his share of support among Colorado Hispanic voters from 61 percent in 2008 to 75 percent in 2012.

If mail ballots boost Hispanic voter participation by a few percentage points this year, it will likely redound to Democrats’ benefit. In a race as tight as the Colorado governor’s race, Hispanic voters could well determine the outcome.

But demographics don’t give the full picture. Since 2008, Democrats have benefited from a much stronger ground game that put operatives in the field to turn out their likely voters.

The effort wasn’t enough to stop populist Tea Party voters from boosting GOP fortunes in the 2010
congressional races, but Colorado was the exception. Democrat Michael Bennet won an open Senate race with just 30,000 more votes than his Republican opponent, Ken Buck.

The question in 2014 is whether mail balloting helps or erases the Democrats’ edge.

A New York Times analysis of Colorado mail ballots that had already been tallied 10 days out from the election seemed to give Republicans an advantage. Registered Republicans had mailed in ballots in higher numbers than Democrats, 42.8 percent to 32.3 percent.

But those trends may not continue. It could be that more Republicans simply cast their ballots early, which is where the Democratic ground game will come in handy.

Early voting makes it easier for “volunteers” — many of them paid political and union operatives — to go door to door to urge those who haven’t voted to do so.

Who is to stop “volunteers” from showing up with dozens of mail ballots collected from elderly voters or others who may have been pressured by union reps or family members to cast their votes?
Colorado will have regulations in place to limit the number of ballots a single individual can drop off at collection centers after 2015, but this year the possibility of ballot stuffing is real.

State election officials claim that the signature on the ballot envelope is their way to detect phony ballots. But the system hardly seems foolproof, requiring signatures to be scanned and matched against a database that may prove more cumbersome than anticipated.

Nov. 4 will be a test for Colorado — and for the nation — on this new experiment in democracy.

View Article Here Read More

Gas falling under $3 per gallon nationwide

October 31, 2014 / Greg Giles / 0 Comments

NEW YORK (AP) — The sight is so surprising that Americans are sharing photos of it, along with all those cute Halloween costumes, sweeping vistas and special meals: The gas station sign, with a price under $3 a gallon.
"It's stunning what's happening here," says Tom Kloza, chief oil analyst at the Oil Price Information Service. "I'm a little bit shocked."
The national average price of gasoline has fallen 33 cents in October, landing Friday at $3.00, according to AAA. Kloza said the average will fall under $3 by early Saturday morning for the first time in four years.
When the national average crossed above $3 a gallon in December of 2010, drivers weren't sure they'd ever see $2.99 again. Global demand for oil and gasoline was rising as people in developing countries bought cars by the tens of millions and turmoil was brewing in the oil-rich Middle East.
Now demand isn't rising as fast as expected, drillers have learned to tap vast new sources of oil, particularly in the U.S., and crude continues to flow out of the Middle East.
Seasonal swings and other factors will likely send gas back over $3 sooner than drivers would like, but the U.S. is on track for the lowest annual average since 2010 — and the 2015 average is expected to be lower even still.
Trisha Pena of Hermitage, Tenn., recently paid $2.57 a gallon to fill up her Honda CRV. Like many around the country these days, she was so surprised and delighted by the price she took a photo and posted it on social media for her friends to see. "I can't remember the last time it cost under $30 to put 10 or 11 gallons in my tank," she said in an interview. "A month ago it was in the $3.50 range, and that's where it had been for a very long time."
Here are a few things to know about cheap gas:
— Crude prices came off the boil. Oil fell from $107 a barrel in June to near $81 because there's a lot of supply and weak demand. U.S. output has increased 70 percent since 2008, and supplies from Iraq and Canada have also increased. At the same time, demand is weaker than expected because of a sluggish global economy.
— In the past, a stronger economy in the U.S., the world's biggest consumer of oil and gasoline, typically meant rising fuel demand. No longer. Americans are driving more efficient vehicles and our driving habits are changing. Michael Sivak of the University of Michigan Transportation Research Institute calculates that the number of miles traveled per household and gallons of fuel consumed per household peaked in 2004.
— The drop from last year's average of $3.51 per gallon will save the typical U.S. household about $50 a month.
— The drop will save the U.S. economy $187 million a day, and also boost the profits of shippers, airlines, and any company that sends employees out on sales calls or for deliveries.
— It will take an extra 1.5 years to make purchasing a higher-priced, better-mileage Toyota Prius instead of a Toyota Corolla pay off.
— New York's average of $3.37 is the highest in the continental U.S. South Carolina and Tennessee are the lowest, with an average of $2.75.
— Politicians are either going to take the credit for lower gasoline prices or blame the other party for not helping them fall further. Don't listen. There are small things politicians can do over long time horizons, like implement fuel economy standards or ease drilling regulations, but the decline in prices is mainly due to market forces.

View Article Here Read More

Some like it hot ~ NASA Stumbles Upon A Dead Star That’s 10 Million Times Brighter Than The Sun

October 18, 2014 / Greg Giles / 0 Comments

This image of the super-bright pulsar (shown here in magenta) was made using observational data from three telescopes, including NASA’s NuSTAR.

Excerpt from
huffingtonpost.com

Think our sun is bright? NASA says its NuSTAR space-based X-ray telescope has detected a dead star that pumps out as much energy as 10 million suns.

"You might think of this pulsar as the 'Mighty Mouse' of stellar remnants," Dr. Fiona A. Harrison, professor of physics and astronomy at the California Institute of Technology in Pasadena and the principal investigator of the NuSTAR mission, said in a written statement.

The super-bright pulsar--the brightest ever recorded--is located about 12 million light-years from Earth in the Messier 82 galaxy. It's an example of a class of mysterious celestial objects known as ultraluminous X-ray sources, or ULXs.

"We took it for granted that the powerful ULXs must be massive black holes," Dr. Matteo Bachetti, an astrophysicist at the University of Toulouse in France and the lead author of a new study about the pulsar, said in the statement.

The X-rays are believed to be generated by the material as it heats up while falling into a dense object, in this case a pulsar.

"How much visible light is emitted is actually an interesting thing to know," Bachetti told The Huffington Post in an email.

In any case, the surprising discovery has scientists scratching their heads.

"This is going to challenge theorists and pave the way for a new understanding of the diversity of these fascinating objects," Dr. Jeanette Gladstone, a University of Alberta astronomer who wasn't involved in the research, said in the statement.

View Article Here Read More

The Unstoppable Awakening of Humanity

September 25, 2014 / Steven Lanier's Journey - Main Article Directory / 0 Comments

by Zen GardnerWe’re undergoing an amazing transformation. Absolutely diametrically opposed to the constant, gradual attempt by elitists to shut down humanity via eons of engineered subjugation, we’re being consciously and vibrationally liberated by the very nature of the Universe in spite of all their efforts.It’s not readily apparent to most, but it’s very clearly there.It’s subtle and yet obvious at the same time. Knowledge of this change or shift in conscio [...]

View Article Here Read More

Cosmic dust may have distorted cosmic inflation breakthrough

September 23, 2014 / Greg Giles / 0 Comments

The 10-meter South Pole Telescope and the BICEP (Background Imaging of Cosmic Extragalactic Polarization) Telescope at Amundsen-Scott South Pole Station, which detected evidence of gravitational waves, is seen against the night sky with the Milky Way in this National Science Foundation picture taken in August 2008.

By Ben P. Stein, Inside Science

Harvard researchers rocked the science community last March with an apparent discovery of gravitational ripples that gave credence to cosmic inflation theory – a finding that met as much skepticism as enthusiasm. Now, further analysis raises more doubts.

"Extraordinary claims require extraordinary evidence." This phrase, popularized by the late Carl Sagan, kept going through my head on March 17, the day that researchers involved with BICEP2, a telescope in Antarctica, made a big announcement at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

The researchers reported that BICEP2 detected gravitational waves from the first moments after the big bang, a feat, which if confirmed, would open up a new field of study and would surely be recognized in a future Nobel Prize.

Gravitational waves are ripples in space and time. They're created when any object with mass accelerates. However, they're extremely weak, making them very hard to detect directly. Even for the most massive and cataclysmic events, such as the collision of two black holes, their effects, observed from Earth, are very hard to detect.

If you're looking for a detectable gravitational wave signal, what bigger event can there be than cosmic inflation? According to inflation theory, the universe multiplied its size by as much as 10 trillion trillion trillion times in the first fractions of a second after the big bang. Inflation would have generated lots of gravitational waves. In turn, gravitational waves can subtly change the properties of light that they pass through. Specifically, they can slightly affect the polarization of light, the direction in which light's electric fields vibrate. The universe's rapid expansion during inflation would have amplified the waves' imprint on the early light in the universe.

The state-of-the-art BICEP2 experiment, which uses super-sensitive superconducting sensors, could detect tiny changes in polarization in the cosmic microwave background, the very first light released in the universe, which is still reaching us today. The BICEP2 researchers reported a very high polarization signal, known as B-mode polarization after its characteristics, in the cosmic microwave background, which they interpreted as a strong gravitational wave signal in the early universe.

Detecting this polarization signal was a striking result, announced in a series of scientific talks and a press conference shortly after a preprint of the paper was posted online. Notice these last two points: announced at a press conference, and a preprint posted online. A preprint is a written paper that has not been formally reviewed by independent peers or published in a scientific journal.

Nonetheless, scientists and reporters alike reported excitement over the results. If true, they would provide the greatest experimental support yet of cosmic inflation, and the first direct detection of gravitational waves. Previously, gravitational waves have been detected indirectly, such as in observations of pairs of stars falling towards each other: they were losing energy in the form of gravitational waves.

On the day of the BICEP2 announcement, and for many days afterward, people were largely accepting the results as correct and already jumping to the implications of the BICEP2 results for what appeared to be a new era of gravitational-wave cosmology.

In writing my story for Inside Science News Service, I was fortunate to get an early voice of skepticism from David Spergel, a theoretical cosmologist at Princeton University in New Jersey. He commented:

"Given the importance of this result, my starting point is to be skeptical. Most importantly, there are several independent experimental groups that will test this result in the next year."

Spergel explained that the new gravitational wave measurements did not appear to agree with those of previous experiments, known as WMAP and Planck, unless the simplest models of inflation were replaced by more complicated ones. On the first day and week of coverage, I became very disappointed with the many commentators who disregarded or underemphasized that the earlier measurements from instruments on WMAP and Planck, which had been reported and covered for years.

Sure enough, in the weeks that followed, other researchers pointed out that the signal that BICEP2 detected may have been attributable to the polarization of light caused by dust in our galaxy. The BICEP2 team certainly knew that dust could also polarize light in a similar way to gravitational waves, but they used a model, based on the data that was available from the Planck satellite, that, the other researchers pointed out, may have underestimated the amount of dust in the part of the sky they were studying.

The BICEP2 paper underwent peer review and was published in Physical Review Letters. As a result of the peer-review process, the researchers made revisions, including removing the model that contained the lower estimates of dust based on the earlier Planck data, and thereby reducing the certainty with which they could state that they accounted for signals from interstellar dust.

During the summer, the BICEP2 and Planck collaborations agreed to work together to analyze their data, to help determine if gravitational waves had really been detected.

This week, the Planck team issued a preprint, based on an analysis of much additional data, showing a comprehensive map of dust in the sky. According to their analysis, the signal in the part of sky that BICEP2 analyzed could be completely attributable to dust and not to gravitational waves.

But, the story is not over. For starters, keep in mind the new preprint, like all newly posted publications, still needs to undergo formal peer review.

And the latest data do not completely rule out the possibility that the BICEP2 group detected a gravitational wave signal. If the evidence holds up at all, it would likely be a weaker signal, after accounting for the dust. Or, the gravitational-wave signal may completely turn to dust.

It may be possible to detect primordial gravitational waves in a different, less dusty part of the sky, or with new measurements by BICEP2, Planck or the many other experiments that are looking for them. Just as the first reported detections of exoplanets turned out to be false, perhaps this is a prelude to an actual detection of gravitational waves.

"You cannot ignore dust," he quotes from Planck scientist Charles Lawrence of NASA’s Jet Propulsion Laboratory in Pasadena, California.

The biggest lesson, to me, is that no one should rush to make announcements and pronouncements, whether big or small, even in the face of intense competition and the alluring prospects of launching a new field of study and winning a Nobel Prize.

Scientists, and the rest of the public, should follow the time-tested scientific practice of subjecting claims to sufficient levels of scrutiny, and waiting for other groups to validate results, before making bold statements. At the very least, there have been major caveats and qualifiers in announcing new data with potentially huge implications.

View Article Here Read More

Space station detector reports more hints of dark matter—or not

September 19, 2014 / Greg Giles / 0 Comments

Adrian Cho

New reports of further evidence for dark matter have been greatly exaggerated. Yesterday, researchers working with the Alpha Magnetic Spectrometer (AMS), a $2 billion cosmic ray detector attached to the International Space Station, reported their latest data on a supposed excess of high-energy positrons from space. They contended—at least in a press release—that the new results could offer new hints that they’ve detected particles of dark matter, the mysterious stuff whose gravity binds the galaxies. But several cosmic ray physicists say that the AMS data are still perfectly consistent with much more mundane explanations of the excess. And they doubt AMS alone will resolve the issue.
The leader of the AMS team, Nobel laureate Samuel Ting of the Massachusetts Institute of Technology in Cambridge, takes care to say that the new results do not prove that AMS has detected dark matter. But he also says the data lend more support to that interpretation than to some others. "The key statement is that we have not found a contradiction with the dark matter explanation," he says.
The controversy centers on AMS's measurement of a key ratio, the number of antimatter positrons to the sum of positrons and electrons. In April 2013, AMS confirmed early reports that as the energy of the particles increased above about 8 gigaelectron Volts (GeV), that ratio, or "positron fraction," increased, even as the individual fluxes of electrons and positrons were falling. That increase in the relative abundance of positrons could signal the presence of dark matter particles. According to many theories, if those particles collide, they would annihilate each other to produce electron-positron pairs. That would alter the balance of electrons and positrons among cosmic rays, as the usual source such as the cloudlike remnants of supernova explosions produce far more electrons than positrons.
However, that interpretation was hardly certain. Even before AMS released its measurement of the ratio, astrophysicists had argued that the excess positrons could potentially emanate from an undetected nearby pulsar. In November 2013, Eli Waxman, a theoretical astrophysicist at the Weizmann Institute of Science in Rehovot, Israel, and colleagues went even further. They argued that the excess positrons could come simply from the interactions of "primary" cosmic rays from supernova remnants with the interstellar medium. If so, then the positrons were just "secondary" rays and nothing to write home about.
However, AMS team researchers see two new features that are consistent with the dark matter interpretation, they reported online yesterday in Physical Review Letters. First, the AMS team now sees that after rising with energy, the positron fraction seems to level off and may begin to fall at an energy of 275 GeV, as would be expected if the excess were produced by colliding dark matter particles, as the original particles' mass would put an upper limit on the energy of the positron they spawned. AMS researchers say the leveling off would be consistent with a dark matter particle with a mass of 1 teraelectron volt (TeV). (Thanks to Albert Einstein’s famous equivalence of mass and energy, the two can be measured in the same units.)
Second, the AMS team measured the spectra of electrons and positrons individually. They found that the spectra have different shapes as energy increases. "It's really surprising that the electrons and positrons are so different," Ting says. And, he argues, the difference suggests that the positrons cannot be secondary cosmic rays produced by primary cosmic ray electrons, as such production should lead to similar spectra.
But some cosmic ray physicists aren't convinced. For example, in AMS's graph of the electron fraction, the error bars at the highest energies are large because the high-energy particles are so rare. And those uncertainties make it unclear whether the positron fraction really starts to drop, says Stéphane Coutu, a cosmic ray physicist at Pennsylvania State University, University Park. And even if the positron fraction does fall at energies higher than AMS reported, that wouldn't prove the positrons come from dark matter annihilations, Coutu says. Such a "cutoff" could easily arise in positrons from a pulsar, he says, if the spatial region in which the pulsar accelerates particles is of limited size. All told, the new results are "probably consistent with anything," Coutu says.
Similarly, Waxman questions Ting's claim that the new data suggest the positrons aren't simply secondary cosmic rays. If that were the case, then the electrons and positrons would be coming from different places and there would be no reason to expect their spectra to be similar, Waxman says. Moreover, he notes, AMS's measurement of the positron fraction seems to level out just at the limit that he and colleagues predicted would be the maximum achievable through secondary cosmic rays. So, in fact, the new data support the interpretation that the positrons are simply secondary cosmic rays, he says. "To me this is a very strong indication that we are seeing cosmic ray interactions.”
Will the argument ever end? AMS is scheduled to take data for 10 more years, which should enable scientists to whittle down the uncertainties and extend their reach toward higher energies, Ting says. "I think we should be able to reach 1 TeV with good statistics," he says, and that should be enough to eventually settle the dispute. But Gregory Tarlé, an astrophysicist at the University of Michigan, Ann Arbor, says, "I don't think that's a legitimate claim." Higher energy cosmic rays arrive at such a low rate that even quadrupling the data set would leave large statistical uncertainties, he says. So, Tarlé suspects, years from now the AMS results will likely look about as ambiguous they do now.

View Article Here Read More