Space station could test ‘spooky’ entanglement over record distance

Space station could test ‘spooky’ entanglement over record distance


“Spooky” quantum entanglement connects two particles so that actions performed on one reflect on the other. Now, scientists propose testing entanglement over the greatest distance yet via an experiment on the International Space Station.

Until now, entanglement has been established on relatively small scales in labs on Earth. But now physicists propose sending half of anentangled particle pair to the space station, which orbits about 250 miles (400 kilometers) above the planet.

“According to quantum physics, entanglement is independent of distance,” physicist Rupert Ursin of the Austrian Academy of Sciences said in a statement. “Our proposed Bell-type experiment will show that particles are entangled, over large distances — around 500 kilometers — for the very first time in an experiment.”

Ursin and his colleagues detail the proposed experiment on Monday in the New Journal of Physics, published by the Institute of Physics and the German Physical Society.[Wacky Physics: The Coolest Little Particles in Nature]

Tests of quantum entanglement are called Bell tests after the late Northern Irish physicist John Bell, who proposed real-world checks of quantum theories in the 1960s. Entanglement is one of the weirdest quantum predictions, positing that entangled particles, once separated, can somehow “communicate” with each other instantly. The notion unsettled Albert Einstein so much he famously called it “spooky action at a distance.”

To better understand entanglement and test its limits, the researchers suggest flying a small device called a photon detection module to the International Space Station, where it could be attached to an existing motorized Nikon 400mm camera lens, which observes the ground from the space station’s panoramic Cupola window.

Once the module is installed, the scientists would entangle a pair of light particles, called photons, on the ground. One of these would then be sent from a ground station to the device on the orbiting lab, which would measure the particle and its properties, while the other would stay on Earth. If the particles keep their entangled state, a change to one would usher in an instant change to the other. Such a long-range test would allow the physicists to probe new questions about entanglement.

“Our experiments will also enable us to test potential effects gravity may have on quantum entanglement,” Ursin said.

The project should be relatively quick to perform during just a few passes of the space station over the ground lab, with each experiment lasting just 70 seconds per pass, the researchers said.

“During a few months a year, the ISS passes five to six times in a row in the correct orientation for us to do our experiments,” Ursin said.”We envision setting up the experiment for a whole week and therefore having more than enough links to the ISS available.”

The researchers also proposed a related experiment to try sending a secret key used for quantum information encryption over the farthest distance yet via theInternational Space Station. Until now, quantum encryption keys have been sent over only relatively short distances on Earth. If the key can be transferred via the researchers’ proposed method, it could help to enable more practical quantum encryption.


Skimming the Surface: The Return of Tesla’s Surface Waves

Skimming the Surface: The Return of Tesla’s Surface Waves

A hundred years ago, electrical pioneer Nikola Tesla was working on a radical new type of radio using waves that skim the surface of the earth rather than radiate into space. Tesla believed he could transmit signals across the Atlantic using these surface waves but never succeeded in his lifetime, and the idea faded into relative obscurity. Today it’s back, with the promise of a new system for high-speed data transmission that would combine the benefits of wired and wireless communication.

Surface waves, or electromagnetic waves, which tend to follow the contours of a surface, had been proven to exist mathematically in Tesla’s time. But their practical use was debated. Because they follow the curvature of the earth, surface waves can reach a distant receiver on the ground that is beyond the horizon. “An inexpensive instrument, not bigger than a watch, will enable its bearer to hear anywhere, on sea or land, music or song, the speech of a political leader, the address of an eminent man of science, or the sermon of an eloquent clergyman,” Tesla wrote in 1908.

Tesla’s attempt at long-range radio failed, apparently because the theoretical physicists neglected a factor that meant the waves could cancel themselves out. But these days, thanks to different wavelengths and materials, scientists are overcoming those problems and creating radio transmissions that can reach over the horizon.

At high frequencies, a type of surface wave called Zenneck waves can propagate along a surface. They travel better on some materials than others, but performance is best with a conductor covered in a dielectric material. As with wires, these surfaces can carry high bandwidth, are secure, do not cause interference, and require little power. But as with wireless communication, physical contact is not required.

Janice Turner and colleagues atRoke Manor Research of Romsey, U.K., have developed a Zenneck wave demo unit. This can transmit high-definition video over a length of conductor covered with dielectric with a bandwidth of up to 1.5 gigabits per second. Because Zenneck waves do not extend far from the surface there is no interference with electronics and no frequency-licensing issues as there are with other radio-frequency systems. Turner says that tears or breaks in a surface do not cut the connection, making it more robust than wiring, and it’s inexpensive to manufacture.

One of the first applications for Roke Manor’s waves is likely to be onboard communications on aircraft and satellites. For example, sensors embedded in an aircraft wing could easily communicate with a central computer via surface waves that travel along the wing and fuselage. Satellite components could send data to each other at high speed without the need for complex connectors. Ships are another likely market, because their metal walls block wireless communication.

Turner’s team is also looking at wearable wireless gadgets. A lapel camera or a pulse-sensing wristband could connect to a smartphone in your pocket. Such gadgets already exist, but communicate with a phone via Wi-Fi or Bluetooth. This approach has lower power requirements and higher bandwidth, Turner says. They have also had enquiries about using surface waves to recharge devices wirelessly, and this is possible—in principle.

Meanwhile, surface waves are also proving valuable for long-range radar, like the new High Frequency Surface Wave Radar (HFSWR) that the defense contractor Raytheon is developing. Some of the first radar operated via surface waves, and the U.S. Navy used surface-wave radar in the 1950s, but the technology ultimately lost out to other types—in particular, the sky-wave radar in which the signal is reflected back from the ionosphere.

However, normal radar has a serious limitation: It operates within line of sight, which makes objects close to the surface difficult to spot. This is why airborne radar was developed, to prevent intruders from slipping in below the radar. But maintaining continuous radar coverage from the air is expensive and requires a lot of manpower.

Surface-wave radar provides an alternative, because the signal clings to the sea surface and follows the curvature of the earth. Tony Ponsford, technical director for HF Radar at Raytheon Canada, says that that latest version can track ships at about 230 miles from land. (The surface waves work best over a conductive surface, so this type of radar has a much longer range over salt water than over fresh water or land.) Raytheon is building the device for the Canadian government to help manage the country’s exclusive economic zone, a region that extends to that distance out to sea. It will undergo operational evaluation later this year.

Raytheon’s HFSWR incorporates a number of features to operate safely in the crowded high-frequency band. If it detects another signal on the same wavelength, such as a radio transmission, it automatically switches to a different wavelength. Raytheon says its patented set of algorithms removes clutter so shipping can be picked out more easily.

This type of radar can be used to track cargo vessels, watch for illegal trawling or dumping, and help with search-and-rescue operations. It can also track smugglers, as it is capable of picking up small go-fast boats. It can even detect icebergs; although obviously nonmetallic, they create a disturbance that shows up “like a hole in the sea,” Ponsford says.

Beyond what Raytheon and Roke Manor are doing in the field, there is also some classified military work on surface waves. Some of this appears to be focusing on covert communications, using the unique properties of surface waves to send a signal that cannot be intercepted, over either land or water.

Although scientists have known about them for more than a century, these are in some ways still early days for surface waves. They have so far been exploited in only very limited ways compared to other forms of radio wave, but that may be set to change. Perhaps Tesla’s faith in surface waves was simply a sign that he was ahead of his time.

Your 7-Step Guide to the Shadow Universe

Your 7-Step Guide to the Shadow Universe

Five-sixths of the universe is missing. That statement feels strange to write, and I’m sure it feels pretty strange to read as well. Given the vastness of the cosmos–and given how little of it humans have explored–how can we know for sure that anything is out of place? The claim sounds positively arrogant, if not delusional.

Color-coded, composite of the galaxy cluster Abell 520. Green denotes hot gas; orange highlights starlight from galaxies; blue shows the inferred location of dark matter. (Credit: NASA, ESA, CFHT, CXO, M.J. Jee, and A. Mahdavi)

And yet scientists have assembled a nearly airtight case that the majority of the matter in the universe consists dark matter, a substance which is both intrinsically invisible and fundamentally different in composition than the familiar atoms that make up stars and planets. In the face of staggering difficulties, researchers like Samuel Ting of MIT are even making progress in figuring out what dark matter is, as evidence by teasing headlines from last week. Time to come to terms, then, with the new reality about our place in the universe. Here are seven key things every informed citizen of the cosmos should know.

1 Dark matter is real. The evidence for dark matter goes all the way back to apaper published by visionary Swiss astronomer Fritz Zwicky in 1933–less than a decade after Edwin Hubble definitively proved the existence of other galaxies. Zwicky noticed that galaxies in clusters were moving so quickly that the clusters should be flying apart, and yet the clusters remain intact. He concluded that there must be dunkle Materie (dark matter) scattered through the clusters, providing the extra gravitational pull that holds everything together. At the time, most of Zwicky’s colleagues considered the evidence too tentative, and the idea too weird, to believe. In the 1970s, American astronomer Vera Rubin changed their minds with the same kind of observations carried out in much greater detail. She found that galaxies systematically rotate so quickly that they should fly apart unless bound together by dark matter–or unless our understanding of the laws of gravity are wrong. More recently, astrophysicists have run elaborate computer models of how galaxies form. These models beautifully fit the observed structure of the universe, but only if they include dark matter into their equations.

Galaxy rotation

Stars in the outer regions of spiral galaxy M74 move much more quickly than expected if they were held in orbit only by the visible matter. The best explanation is that they are being pulled by a large halo of unseen, dark matter. (Credit: Gemini Observatory/GMOS Team)

Two other lines of evidence strongly support dark matter. One comes from observations of gravitational lensing, the bending of light due to gravity. Astronomers can make crude maps of where the matter is in galaxy clusters by observing how they distort the light of more distant galaxies. These maps not only confirm the presence of huge amounts of dark matter, they also show that the dark stuff moves independentlyfrom hot gas in the cluster, something that alternate theories of gravity cannot easily explain. Another, completely independent line of evidence comes from studies of the cosmic microwave background, radiation left over from the Big Bang. The distribution of that radiation on the sky is very sensitive to the exact composition of the early universe. The observed pattern allows a very precise measurement of the makeup of the universe, as I described recently, in which dark matter outweighs visible matter by a factor of 5.5 to 1. All three types of observations not only show evidence of dark matter, they also show the same amount of dark matter. That’s awfully persuasive.

2. Dark matter can be visible…sometimes. That sounds like a contradiction of all that I’ve just said, so bear with me. Dark matter seems not to interact with light or any other form of electromagnetic radiation (radio, x-rays, etc), but it may be able to interact with itself. One of the leading theories of dark matter holds that it consists of fundamental particles called WIMPs (weakly interacting massive particles) that can destroy each other if they happen to smack into each other. In the vastness of space, particles don’t collide very often but it will inevitably happen occasionally. If two WIMPs annihilate each other, they might create visible radiation in the form of gamma rays; or they might give rise to more familiar types of particles, such as electrons and their antimatter partners, positrons.

In fact, two space-based experiments are currently looking for both signals, and both see some intriguing signs of something strange going on in the depths of space. NASA’s Fermi Gamma-Ray Space Telescope has picked up an extremely faint but unusual glow of gamma rays having a very specific energy: 130 giga-electron volts (GeV), or about 60 billion times the energy of visible light. That looks a lot like the breakdown of a dark-matter particle, but Christoph Weniger of the Max-Planck Institute for Physics cautions that the evidence right now “is as ambiguous as it can be.” Further hints of dark matter come from Samuel Ting and the $2 billion Alpha Magnetic Spectrometer, or AMS, experiment aboard the International Space Station. That’s the one that just made headlines last week. (New York Times: “Tantalizing New Clues into the Mysteries of Dark Matter”.) AMS is picking up a slight excess of positrons from all directions of the sky, which is again consistent with the presence of dark matter but not yet at all conclusive. Stay tuned for more results; Ting says it will take “several more years” before he has enough data to say for sure.


The Alpha Magnetic Spectrometer experiment (top left) aboard the International Space Station. (Credit: NASA/AMS)

3. Dark matter might show up here on Earth. In theory, we are swimming in dark matter all the time. It should be passing through you right now. Because dark matter is so unreactive, most of the time it keeps going and nobody here is any the wiser for it. But starting in the 1990s, a few hardy (or foolhardy, depending on your perspective) physicists decided to try to sense dark matter particles as they pass. The idea is that on very rare occasions, a dark matter particle might strike an atom of ordinary matter, giving it a kick. That could potentially be detected as a thermal signal: a minuscule dose of heat. Several experiments along these lines have claimed tentative sightings of dark matter signals. The most celebrated results have come from the detector known as DAMA, short simply for DArk MAtter. Beyond a core of true believers, nobody considers these results convincing, however. A new experiment called LUX should clarify the situation. “The sensitivity is significantly better than previous direct detection experiments,” promises LUX principle investigatorRichard Gaitskell of Brown University. By the time LUX finishes its first full run in 2015 it will be, he hopes, “a very definitive experiment.”

4. We might be able to create our own dark matter. That is one of the great goals for the ambitious Large Hadron Collider: making dark matter in the lab so that scientists can study it. The core concept of the LHC is that the mad smashing of particles into other particles will shake loose all kinds of things that do not show up in the calm and quiet of everyday physics. In essence, the huge amounts of energy created at the LHC can be spontaneously transformed into various particles (mass and energy being equivalent–remember your e=mc²?). That is how the physicists at the LHC (probably) found the Higgs Boson. If WIMPs have the kinds of masses that theorists expect, the LHC should create them too. Such dark matter particles will be hard to track down, because of their elusive nature. They tend to fly right out of the detectors, unseen, and so would initially show up as missing energy in the LHC reactions: One more shadow to chase. Still, if the WIMPs really are there, the crafty researchers and enormous computers that sift through data from the LHC should be able to find them when thecollider restarts in 2015.

5. Dark matter is a totally different thing than dark energy. In 1998, two competing teams of cosmologists discovered that the expansion of the universe is speeding up. The force behind that cosmic expansion is now known as “dark energy,” a term that was coined byMichael Turner at the University of Chicago as a deliberate (if sometimes confusing) counterpoint to dark matter. Both are dark in the sense that they are unseen, and both are dark in the sense that they are mysterious. But dark matter seems to consist of some sort of particles, and it exerts a gravitational pull that tends to bring things together: it glues together galaxies and galaxy clusters, and may have provided the extra attraction that allowed these structures to form in the first place. Dark energy, on the other hand, is even less well understood but it seems to be a form of energy that is embedded into the fabric of space itself, and it exerts a repulsive force–almost like antigravity–over extremely long distances. To add further confusion, dark energy has the equivalent of mass (if you didn’t remember your e=mc² before, try remembering it now) and when you total up all that mass, dark energy is the dominant component of the universe.

6. The dark stuff really dominates.Based on the latest observations from the Planck observatory, the universe consists of 68.3 percent dark energy, 26.8 percent dark matter, and 4.9 percent ordinary matter. A little perspective: More than 95 percent of the universe is dark and fundamentally unobservable, most of the universe does not consist of matter, and most of the matter does not consist of atoms like the ones that make up you and me. Feeling insignificant yet?

7. The dark universe might have a life of its own. A few years back, Savas Dimopoulos of Stanford University postulated that dark matter could form dark atoms that create their own dark chemistry. Neal Weiner at NYU has kicked around the thought problem of how a hypothetical scientist composed of dark matter might be able to find the visible universe (which of course would be invisible to him or her). The answer: It wouldn’t be easy. And just recently a group of Harvard University physicists led by JiJi Fan and Lisa Randall have theorized that some dark matter might be able to cool and collapse just the way ordinary hydrogen gas does, leading to the possibility of dark galaxies, perhaps even dark stars and dark planets.

Right now nobody knows. Perhaps these ideas are just flights of fantasy, but they are fantasies that are consistent with what we currently understand about how the universe works. In fact, they are supported by some of the best available current observations. Douglas Finkbeiner, an astrophysicist at Harvard, neatly sums up the wonder and uncertainty of this kind of research: “We should all be lying in bed awake wondering what dark matter is.”

Fusion Rocket Would Shoot People To Mars In 30 Days

Fusion Rocket Would Shoot People To Mars In 30 Days

Rocket Test Chamber The magnetic chamber for heating deuterium plasma University of Washington, MSNW

One team will be testing fusion propulsion this summer in Redmond.

A research team in Washington state is on its way to making a fusion rocket that could carry people to Mars in 30 days, NBC News reported.

Scientists spent much of the last century trying to harness fusion energy, but never succeeded. NASA funded this latest effort through its Innovative Advanced Concepts program, which the agency describes as a program for creative ideas that may be 10 years or more away from use on a mission. Phase II projects, such as this fusion rocket, received about $600,000 over three years.

The Washington team members include physicists from the University of Washington who say they’ve demonstrated all of the parts of their technology. They now need to combine the components into one experiment that creates energy.

The team’s idea is to use a strong magnetic field to fuse a series of metal rings into a shell around a deuterium plasma. The shell compresses the plasma, creating a fusion reaction that lasts just 25 millionths of a second, NBC News reported. The reaction heats the metal shell and blasts it out of the back of the rocket at 67,000 miles per hour, propelling the rocket. The team hopes that with enough of these brief reactions, they can push a rocket along continually, all the way to Mars.

The team members, led by University of Washington aeronautics researcher John Slough, have heated deuterium plasma up to fusion temperatures. They’ve also tested their magnetic field. They plan to put the two together late this summer, NBC News reported. The experiment will take place at the University of Washington’s Plasma Dynamics Lab in Redmond.

Physicists hunt for five mysterious particles deep underground

Physicists hunt for five mysterious particles deep underground


While the world’s largest atom smasher was busy finding the Higgs boson — the particle thought to explain why other particles have mass — physicists have been quietly building giant laboratories deep underground.

No, scientists aren’t hiding the next James Bond supervillain down there. Instead, they are working more than a mile beneath Earth’s surface to find some of the universe’s most elusive particles.

The layers of rock may harbor evidence of a new force and shield delicate experiments from cosmic rays and other high-energy particles, allowing ultra-rare particles to reveal themselves. Here are some mysterious particles that could be lurking underground.

The unparticle
Physicists are hunting for a new fundamental force within Earth’s mantle.The unparticle, which has some of the characteristics of massless photons as well as mass-bearing particles, could be responsible for long-range spin interactions, a new force that causes the electrons in atoms to align their spins over long distances.

To find evidence of the new force, researchers mapped out the electron density and spin within Earth’s mantleand are now investigating whether these subterranean electrons are affecting how neutrons and electrons spin in two experiments separated by about 3,000 miles (4,828 kilometers). If the electrons in the mantle are transmitting a force to those particles in lab experiments, it should change the frequency at which they spin. Then the new force would join gravity, electromagnetism and the strong and weak nuclear forces in dictating the behavior of the universe. [50 Amazing Facts About Planet Earth]

Dark-matter particles
The universe is filled with invisible stuff called dark matter, whose gravitational pull is thought to keep galaxies from flying apart. Leading theories propose that dark matter is made up of weakly interacting massive particles, or WIMPs, that rarely interact with ordinary matter.

Several labs, including the Large Underground Xenon (LUX) Detector in Homestake, S.D., rely on Earth’s crust to shield experiments from cosmic rays that could drown out the few interactions of WIMPs with regular atoms. So far, traces of WIMPs have been few and far between, but with several experiments ongoing, evidence of WIMPs could be revealed within the next few years.

Solar neutrinos
Physicists at Gran Sasso National Laboratory, a particle detector buried a mile beneath an Italian mountain, have caught solar neutrinos in the act of changing types, or “flavors.” The sun’s nuclear reactions create these chargeless particles, but leading theories suggest they change flavor as they traveled to Earth. As a result, physicists looking for certain flavors of solar neutrinos have measured fewer solar neutrinos of those flavors than they expected.

Solar neutrinos rarely interact with matter, but by shooting beams of the particles 454 miles (731 kilometers) from the CERN physics lab to the underground lab in Gran Sasso, physicists managed to catch the particles in the act of changing flavor. The finding confirms that neutrinos do change flavor as they travel from the sun.

Finding geoneutrinos
Neutrinos may form at the sun, but they also are produced from radioactive elements within Earth’s mantle. The Gran Sasso Lab also has isolated some of these so-called geoneutrinos, which form when radioactive uranium or thorium decays. The new particles could explain how much heat forms inside the Earth, driving the motion of tectonic plates. To catch these geoneutrinos emanating from the Earth’s mantle, the researchers use an oil-based fluid that scintillates, or gives off light, when subatomic particles bump into the fluid. The researchers identified the geoneutrinos because they emit a positron followed by a neutron when bumping into the atoms of the fluid, which gives of a characteristic flash of light… Read more

Kepler 2.0: Next-Gen Exoplanet Hunter Approved

Kepler 2.0: Next-Gen Exoplanet Hunter Approved

NASA has selected a $200 million mission to carry out a full-sky survey for exoplanets orbiting nearby stars. The space observatory, called the Transiting Exoplanet Survey Satellite (TESS), is scheduled for a 2017 launch.

Like the currently operational Kepler Space Telescope, TESS will be in the lookout for exoplanets that orbit in front of their host stars, resulting in a slight dip in starlight. This dip is known as a “transit” and Kepler has revolutionized our understanding about planets orbiting other stars in our galaxy by applying this effective technique. As of January 2013, Kepler has spotted 2,740 exoplanetary candidates.

PHOTOS: Top Exoplanets for Alien Life

Although Kepler’s powerful optics have allowed astronomers an unprecedented look into multiplanetary systems, identifying worlds as small as Mercury to many times the size of Jupiter, it is restricted to gazing at a small field of view — accounting for a mere 0.28 percent of the sky. Tiny it may be, but 145,000 main sequence stars fill that view, providing us with a gargantuan amount of transit data for hundreds of exoplanets.

But TESS will be surveying the entire sky, supercharging our profound quest to understand how many stars like our own could host worlds, not too dissimilar to Earth, in their habitable zones.

“TESS will carry out the first space-borne all-sky transit survey, covering 400 times as much sky as any previous mission,” said TESS lead scientist George Ricker, of the Massachusetts Institute of Technology (MIT) Kavli Institute for Astrophysics and Space Research (MKI). “It will identify thousands of new planets in the solar neighborhood, with a special focus on planets comparable in size to the Earth.”

“The TESS legacy will be a catalog of the nearest and brightest main-sequence stars hosting transiting exoplanets, which will forever be the most favorable targets for detailed investigations,” added Ricker.

NEWS: Billions of Habitable Worlds in Our Galaxy?

According to a NASA announcement on Friday, “TESS will use an array of telescopes to perform an all-sky survey to discover transiting exoplanets ranging from Earth-sized to gas giants, in orbit around the nearest and brightest stars in the sky. Its goal is to identify terrestrial planets in the habitable zones of nearby stars.”

Kepler was launched in 2009 and recently saw its mission extended to 2016. It is hoped that the space telescope will detect unequivocal evidence for the presence of an Earth-sized world orbiting within its host star’s habitable zone — the region that is not too close and not too far from a star that permits liquid water to exist on a rocky planet’s surface.

Although we are some time off from probing a distant potentially habitable world’s atmosphere for the presence of liquid water or chemical traces of life, Kepler — along with supporting observations by other space- and ground-based instrumentation — is giving us a tantalizing hint of the preponderance of small rocky worlds in the Milky Way. Using Kepler data, astronomers extrapolated an estimated exoplanetary population for the Milky Way earlier this year and arrived at a staggering number: 100 billion. This, in turn, suggests there are many, many multiplanetarysystems out there.

ANALYSIS: Milky Way Crammed With 100 Billion Alien Worlds?

TESS will undoubtedly become the “next generation” of exoplanet hunters, revolutionizing our perspective on our cosmic backyard once again.

Submitted as concepts for NASA’s Explorer program, TESS and the $55 million Neutron Star Interior Composition Explorer (NICER) were chosen from four options as they “offer the best scientific value and most feasible development plans.” NICER will be attached to the space station to measure the “variability of cosmic X-ray sources, a process called X-ray timing, to explore the exotic states of matter within neutron stars and reveal their interior and surface compositions,” according to the NASA news release.

NASA’s Explorer program is intended to provide frequent, low-cost science missions. Satellite missions are capped at $200 million, whereas space station missions are capped at $55 million.

Source: MIT

Image: Artist’s impression of the Transiting Exoplanet Survey Satellite. Credit: MIT Kavli Institute for Astrophysics and Space Research

Dark Matter Signal Possibly Registered on International Space Station

Dark Matter Signal Possibly Registered on International Space Station

PARTICLE CATCHER: The Alpha Magnetic Spectrometer collects high-energy particles on the orbiting International Space Station. Image: AMS/NASA

A $2-billion particle detector mounted on the International Space Station has registered an excess of antimatter particles in space, the experiment’s lead scientist announced April 3. That excess could come from fast-spinning stellar remnants known as pulsars and other exotic, but visible sources within the Milky Way galaxy. Or the antiparticles might have originated from the long-sought dark matter, the hypothetical massive particles that constitute some 27 percent of the universe.

Dark matter makes its presence feltby its gravitational pull, but exactly what it is has remained a puzzle. Some popular explanations for dark matter’s identity suggest that when two dark-matter particles collide, they annihilate to produce antimatter electrons, or positrons. The Alpha Magnetic Spectrometer (AMS), delivered to the space station in 2011 during the penultimate space shuttle mission, was built to detect positrons and other high-energy particles streaming through space, in part to investigate the nature of dark matter. The detector has now collected some 25 billion cosmic-ray particles, including 6.8 million electrons and positrons. The fraction of positrons in the particle mix exceeds what would be naively expected in the absence of dark matter or other unaccounted sources, but the new data lack a distinctive feature predicted of dark matter annihilations.

Dark matter collisions would produce relatively more high- than moderate-energy positrons. But the rise in positrons with increasing energy would continue only up to a point. Beyond a certain energy level, the number of positrons would fall off steeply, AMS spokesperson and Nobel laureate Samuel Ting of the Massachusetts Institute of Technology explained in a seminar at CERN, the European laboratory for particle physics. “The positrons could also come from nearby pulsars, and in such a case the positrons will have a slow drop-off” at higher energies, Ting said. “So the way they drop off tells you everything.”

The AMS data indeed show an increasing share of positrons toward higher energies, but no drop-off, so the origin of the excess particles remains unclear. The European PAMELA mission and NASA’s Fermi spacecraft have found similar trends in recent years, but Ting called AMS the first experiment “to probe in detail the nature of this excess with high sensitivity and precision.” The research will appear in the April 5 issue of Physical Review Letters.

Ting only presented data on positrons with energies of about 350 giga-electron-volts or less but said that AMS will in the coming years catalogue particles up to 1,000 giga-electron volts. So the experiment may soon reveal or disprove the presence of a positron cutoff at higher energies, which would provide a clue to the source of the particles: a steep drop would point to dark matter, and a gradual decline would indicate pulsars are the originators of the positrons.

When pressed by colleagues at the CERN seminar to discuss any data AMS has already collected on higher-energy particles, Ting demurred. “We will publish things when we are absolutely sure,” he said, repeatedly sounding notes of caution and calling for patience. “I think that no one is foolish enough to repeat what we are doing,” he said of the experiment, which was some 18 years in the making. “So we want to make sure we are doing it correctly.”

Table-top astrophysics: How to build a multiverse

Table-top astrophysics: How to build a multiverse

THE heavens do not lend themselves to poking and prodding. Astronomers therefore have no choice but to rely on whatever data the cosmos deigns to throw at them. And they have learnt a lot this way. Thus you can even (see article) study chemistry in space that would be impossible in a laboratory. Some astronomers, though, are dissatisfied with being passive observers. Real scientists, they think, do experiments.It is impossible—not to mention inadvisable—to get close enough to a star or a black hole to manipulate it experimentally. But some think it might be possible to make meaningful analogues of such things, and even of the universe itself, and experiment on those instead.Ben Murdin of the University of Surrey, for example, has been making white dwarfs. A white dwarf is the stellar equivalent of a shrunken but feisty old-age pensioner. It has run out of fuel and is contracting and cooling as it heads towards oblivion—but taking its time about it. As they shrink white dwarfs pack a mass up to eight times the…Read more

Dark matter: Fractional distillation

Dark matter: Fractional distillation

IF YOU thought the Higgs boson was elusive, consider the case of dark matter. The Higgs—the particle that gives other subatomic species mass—was predicted in 1964 but actually nabbed only last year. That 48-year hunt, though, was a breeze compared with the one for dark matter. Physicists have known the stuff must exist since 1933, when Fritz Zwicky, a Swiss astro-physicist, coined the term to describe a substance which cannot be seen but without which visible galaxies would fly apart as they rotate. The latest results from the European Space Agency’s Planck satellite suggest it makes up 85% of all the matter in the universe (up from an earlier estimate of around 80%).Like the Higgs boson, though, the actual particles of which dark matter is composed have proved elusive. Eight decades after Zwicky’s observations, and dozens of experiments later, they remain undetected. But on April 3rd an experiment called the Alpha Magnetic Spectrometer (AMS) offered the most tantalising hints yet.Although Samuel Ting, the Nobel laureate who heads the effort, presented the findings at CERN (Europe’s, and the world’s, principal particle-physics laboratory), they did not…Read more