In an effort to fill in the blanks of the Standard Model of particle physics, science has been conducting a diligent search for a hypothesized particle known as the "sterile neutrino." If discovered, the sterile neutrino would have added to the neutrino family portrait and helped explain a number of puzzles that suggest the existence of more than the three known flavors of neutrinos. Ultimately, such a particle could also help resolve the mystery of the origin of dark matter and the matter/antimatter asymmetry in the universe.

Now, with the latest results from an icy particle detector at the South Pole, scientists are almost certain that there is no such particle.

Neutrinos are ghostly particles with almost no mass and only rarely interact with matter. Trillions of neutrinos will course through your body in the time it takes to read this sentence. There are three known types of neutrinos: muon, electron and tau. Hints of a possible fourth type of neutrino have come from several experiments. Known as the "sterile neutrino," the hypothesized particle would not interact at all with matter except, possibly, through gravity.

Discovering the sterile neutrino would also throw a wrench into the Standard Model, which allows for only the three known types of neutrino. "If you throw in a fourth neutrino, it changes everything," explains Francis Halzen, a University of Wisconsin-Madison professor of physics and principal investigator for the IceCube Neutrino Observatory, a massive detector embedded deep in the ice beneath the South Pole. "Sterile means it doesn't interact with matter itself, although it can dramatically interfere with the way conventional neutrinos do."

The only way to detect a sterile neutrino is to catch it in the act of transforming into one of the other types. The presence of the sterile neutrino has been hinted at by several experiments, including at the Los Alamos National Laboratory in the 1990s and, more recently, at the Daya Bay nuclear reactor facility near Hong Kong. But definitive evidence of the particle's existence has so far eluded scientists.

Now, in a study published today (Aug. 8, 2016) in the journal Physical Review Letters, IceCube researchers may have largely put to rest the notion of this fourth kind of neutrino. In two independent analyses of data from the massive Antarctic detector -- each consisting of a year's worth of data or about 100,000 neutrino events -- the striking feature associated with the sterile neutrino was nowhere to be found, says Halzen.

The analyses were performed using so-called atmospheric neutrinos, neutrinos created when cosmic rays crash into particles in the upper atmosphere of the Earth. The groups conclude that there is 99 percent certainty the eV-mass sterile neutrino hinted at by previous experiments does not exist.

"Like Elvis, people see hints of the sterile neutrino everywhere," says Halzen. "There was this collection of hints, and theorists were convinced it exists."

The groups conducting the analyses scoured the hundreds of thousands of neutrino events that reached the IceCube detector after coursing through the Earth from the sky in the northern hemisphere. Because only neutrinos can travel through the planet unimpeded, the Earth serves as an effective screen, filtering out all other types of particles. IceCube consists of 5,160 light-detecting sensors frozen in crystal clear Antarctic ice more than a mile beneath the South Pole. Neutrinos are detected when they occasionally crash into nuclei, creating a muon and, subsequently, a telltale streak of blue Cherenkov light.

The search conducted by the IceCube teams looked at neutrino events occurring in the 320 GeV to 20 TeV energy range. In this range, Halzen notes, sterile neutrinos would produce a very distinctive signature.

The appeal of a fourth kind of neutrino is that it would help bridge a gap in theory that predicts that some neutrinos from a beam of one type of neutrino emanating from a given source -- be it a nuclear reactor, the sun or the atmosphere -- would change from one kind of neutrino to another as they travel to a distant detector. It would also help solve other cosmological puzzles like the mismatch between matter and antimatter in the universe and the origin of dark matter.

"This new result highlights the versatility of the IceCube Neutrino Observatory," according to Olga Botner, a professor of physics and astronomy at Uppsala University in Sweden and the spokesperson for the IceCube Collaboration. "It is not only an instrument for exploration of the violent universe but allows detailed studies of the properties of the neutrinos themselves."

Failing to detect the elusive particle, however, means physics remains in the dark about the origin of the tiny neutrino mass, or why they have mass in the first place, says Halzen.

The University of Wisconsin/Madison

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In 1999 astronomers focusing on a star at the center of the Milky Way, measured precisely how long it takes the sun to complete one orbit (a galactic year) of our home galaxy: 226 million years. The last time the sun was at that exact spot of its galactic orbit, dinosaurs ruled the Earth. The Solar System is thought to have completed about 2025 orbits during its lifetime or 0.0008 orbit since the origin of humans. When the last red embers of our Sun die out billions of years from now, we will have completed approximately 60 orbits of our home galaxy.

In fact, our Sun's orbit has only happened 20.4 times since the Sun itself formed 4.6 billion years ago. It's estimated that the Sun will continue fusing hydrogen for another 7 billion years. In other words, it only has another 31 orbits it can make before it runs out of fuel.

Is there a genocidal countdown built into the motion of our solar system? Research at Cardiff University suggests that our system's orbit through the Milky Way encounters regular speedbumps - and by "speedbumps," we mean "potentially extinction-causing asteroids."

Our orbit through the Milky Way is not a perfect circle or an ellipse, since the galaxy itself is a landscape of undulating concentrations of mass and complex gravitational fields. As Caleb Scharf observes in The Copernicus Complex, "none of the components of the galaxy are stationary; they, too, are orbiting and drifting in a three-dimensional ballet. The result is that our solar system, like billions of others, must inevitably encounter patches of interstellar space containing the thicker molecular gases and microscopic dust grains of nebulae. It takes tens of thousands to hundreds of thousands of years to pass through one of these regions.

"This may happen only once every few hundred million years," Scharf adds, "but if modern human civilization had kicked off during such an episode, we would have barely seen more than the nearest stars— certainly not the rest of our galaxy or the cosmos beyond. But could our planetary circumstances have been that different and still produced us? Would more changeable orbits in a planetary system, or bad weather, or passage through interstellar clouds, also thwart the emergence of life in some way?

"Phenomena such as these could be bad news, causing hostile surface environments on a planet. So it's a possibility that the planetary requirements for forming sentient life like us will necessarily always present the senses and minds of such creatures with a specific cosmic tableau, a common window onto the universe."

The visualization of the orbit of the Sun (yellow dot and white curve) below around the Galactic Center (GC) in the last galactic year. The red dots correspond to the positions of the stars studied by the European Southern Observatory in a monitoring program.

If future research confirms a Milky Way galaxy-biodiversity link, it would force scientists to broaden their ideas about what can influence life on Earth. "Maybe it's not just the climate and the tectonic events on Earth," says UK paleontologist Bruce Lieberman. "Maybe we have to start thinking more about the extraterrestrial environment as well."

The surge in cosmic-ray exposure could have both a direct and indirect effect on Earth's organisms, said Lieberman. The radiation could lead to higher rates of genetic mutations in organisms or interfere with their ability to repair DNA damage, potentially leading to diseases like cancer.

William Napier and Janaki Wickramasinghe at Cardiff University completed computer simulations of the motion of the Sun in our outer spiral-arm location in the Milky Way that revealed a regular oscillation through the central galactic plane, where the surrounding dust clouds are the densest. The solar system is a non-trivial object, so its gravitational effects set off a far-reaching planetoid-pinball machine which often ends with comets being hurled into the intruding system.

The sun is about 26,000 light-years from the center of the Milky Way Galaxy, which is about 80,000 to 120,000 light-years across (and less than 7,000 light-years thick). We are located on on one of its spiral arms, out towards the edge. It takes the sun -and our solar system- roughly 226 million years to orbit once around the Milky Way. In this orbit, we are traveling at a velocity of about 155 miles/sec (250 km/sec).

Many of the ricocheted rocks collide with planets on their way through our system, including Earth. Impact craters recorded worldwide show correlations with the ~37 million year-cycle of these journeys through the galactic plane - including the vast impact craters thought to have put an end to the dinosaurs two cycles ago.

Almost exactly two cycles ago, in fact. The figures show that we're very close to another danger zone, when the odds of asteroid impact on Earth go up by a factor of ten. Ten times a tiny chance might not seem like much, but when "Risk of Extinction" is on the table that single order of magnitude can look much more imposing.

You have to remember that ten times a very small number is still a very small number - and Earth has been struck by thousands of asteroids without any exciting extinction events. A rock doesn't just have to hit us, it has to be large enough to survive the truly fearsome forces that cause most to burn up on re-entry.

Professors Medvedev and Melott of the University of Kansas have a different theory based on the same regular motion. As the Sun ventures out "above" the galactic plane, it becomes increasingly exposed to the cosmic ray generating shock front that the Milky Way creates as it ploughs through space. As we get closer to this point of maximum exposure, leaving the shielding of the thick galactic disk behind, the Kansas researchers hold that the increasing radiation destroys many higher species, forcing another evolutionary epoch. This theory also matches in time with the dinosaur extinction.

Either way, don't go letting your VISA bill run up just yet. "Very close" in astronomical terms is very, very different to "close" in homo-sapien time.

The characteristic spiral arms of the Milky Way regions where stars and gas are a little closer together -- waves of higher density than elsewhere in our galaxy's disc. Their additional gravity is normally too weak to alter a star's path by much, but if the star's orbital speed happens to match the speed at which the spiral arm is itself rotating, then the extra force has more time to take effect.

Simulations completed by Rok Roskar of the University of Zurich, Switzerland, show that a lucky star can ride the wave for 10,000 light years or more. Our sun is an example, with some measurements implying that the sun is richer in heavy elements than the average star in our neighborhood, suggesting it was born in the busy central zone of the galaxy, where stellar winds and exploding stars enrich the cosmic brew more than in the galactic suburbs. The gravitational buffeting the solar system received then might also explain why Sedna, a large iceball in the extremities of the solar system, travels on a puzzling, enormously elongated orbit.

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The Daily Galaxy via The Copernicus Complex, cardiff.ac.uk and newscientist.com

Image credit: with thanks to ucl.ac.uk

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“The first person to live to be 1,000 years old is certainly alive today …whether they realize it or not, barring accidents and suicide, most people now 40 years or younger can expect to live for centuries,” claims Cambridge University geneticist Aubrey de Grey. "The only difference between my work and the work of the whole medical profession," de Grey adds, "is that I think we're in striking distance of keeping people so healthy that at 90 they'll carry on waking up in the same physical state as they were at the age of 30, and their probability of not waking up one morning will be no higher than it was at the age of 30."

The image above is one of 100 cast-iron life-size human figures by British sculptor Anthony Gormley that explore the place of humanity in nature. Gormley who has created and installed them high in the Alps, scattered over 150 sq km (58 sq miles) of some of Austria's most dramatic scenery.

“I just don't think [immortality] is possible,” countered Sherwin Nuland, a former professor of surgery at the Yale School of Medicine. “Aubrey and the others who talk of greatly extending lifespan are oversimplifying the science and just don't understand the magnitude of the task. His plan will not succeed. Were it to do so, it would undermine what it means to be human.”

Perhaps de Gray is way too optimistic, but others have joined the search for a virtual fountain of youth. In fact, a growing number of scientists, doctors, geneticists and nanotech experts—many with impeccable academic credentials—are insisting that there is no hard reason why ageing can't be dramatically slowed or prevented altogether. Not only is it theoretically possible, they argue, but a scientifically achievable goal that can and should be reached in time to benefit those alive today.

“I am working on immortality,” says Michael Rose, a professor of evolutionary biology at the University of California, Irvine, who has achieved breakthrough results extending the lives of fruit flies. “Twenty years ago the idea of postponing aging, let alone reversing it, was weird and off-the-wall. Today there are good reasons for thinking it is fundamentally possible.”

Even the US government finds the field sufficiently promising to fund some of the research. Federal funding for “the biology of ageing”, excluding work on ageing-specific diseases like heart failure and cancer has been running at about $2.4 billion a year, according to the National Institute of Ageing, part of the National Institutes of Health.

So far, the most intriguing results have been spawned by the genetics labs of bigger universities, where anti-ageing scientists have found ways to extend live spans of a range of organisms—including mammals. But genetic research is not the only field that may hold the key to eternity.

“There are many, many different components of ageing and we are chipping away at all of them,” said Robert Freitas at the Institute for Molecular Manufacturing, a non-profit, nanotech group in Palo Alto, California. “It will take time and, if you put it in terms of the big developments of modern technology, say the telephone, we are still about 10 years off from Alexander Graham Bell shouting to his assistant through that first device. Still, in the near future, say the next two to four decades, the disease of ageing will be cured.”

But not everyone thinks ageing can or should be cured. Some say that humans weren't meant to live forever, regardless of whether or not we actually can.

It's interesting that Nuland first says he doesn't think it will work but then adds that if it does, it will undermine humanity. So, which is it? Is it impossible, or are the skeptics just hoping it is?

After all, we already have overpopulation, global warming, limited resources and other issues to deal with, so why compound the problem by adding immortality into the mix.

But anti-ageing enthusiasts argue that as our perspectives change and science and technology advance exponentially, new solutions will emerge. Space colonization, for example, along with dramatically improved resource management, could resolve the concerns associated with long life. They reason that if the Universe goes on seemingly forever—much of it presumably unused—why not populate it?

However, anti-ageing crusaders are coming up against an increasingly influential alliance of bioconservatives who want to restrict research seeking to “unnaturally” prolong life. Some of these individuals were influential in persuading President Bush in 2001 to restrict federal funding for embryonic stem cell research. They oppose the idea of life extension and anti-ageing research on ethical, moral and ecological grounds.

Leon Kass, the former head of Bush's Council on Bioethics, insists that “the finitude of human life is a blessing for every human individual”. Bioethicist Daniel Callahan of the Garrison, New York-based Hastings Centre, agrees: “There is no known social good coming from the conquest of death.”

Maybe they're right, but then why do we as humans strive so hard to prolong our lives in the first place? Maybe growing old, getting sick and dying is just a natural, inevitable part of the circle of life, and we may as well accept it.

"But it's not inevitable, that's the point," de Grey says. "At the moment, we're stuck with this awful fatalism that we're all going to get old and sick and die painful deaths. There are a 100,000 people dying each day from age-related diseases. We can stop this carnage. It's simply a matter of deciding that's what we should be doing."

The Daily Galaxy via worldhealth.net and BBC News

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Matching bite marks in food at a crime scene to a suspect's teeth is often a stretch. Saliva deposited on the food and subjected to DNA analysis, however, has the potential to strengthen the positive identification of those present at a crime. (Flickr photo by Jacovn117*)

During biting, saliva is often deposited by the teeth and lips in enough quantity to allow its later collection and use in DNA typing. (Flickr photo by Gregg O'Connell)

Ample saliva was collected from the apples in the study, but acidic compounds in the apple's juice deteriorated the DNA while it was at room temperature. No quality DNA was amplified from the apple. (Flickr photo by Erich Ferdinand)

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