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.
Google Chairman Eric Schmidt: "The Internet Will Disappear"
Excerpt from hollywoodreporter.com
Google executive chairman Eric Schmidt on Thursday predicted the end of the Internet as we know it.
At the end of a panel at the World Economic Forum in Davos, Switzerland, where his comments were webcast, he was asked for his prediction on the future of the web. “I will answer very simply that the Internet will disappear,” Schmidt said.
“There will be so many IP addresses…so many devices, sensors, things that you are wearing, things that you are interacting with that you won’t even sense it,” he explained. “It will be part of your presence all the time. Imagine you walk into a room, and the room is dynamic. And with your permission and all of that, you are interacting with the things going on in the room.”
Concluded Schmidt: “A highly personalized, highly interactive and very, very interesting world emerges.”
The panel, entitled The Future of the Digital Economy, also featured Facebook COO Sheryl Sandberg and others.
Earlier in the debate, Schmidt discussed the issue of market dominance. The European Union has been looking at Google’s search market dominance in a long-running antitrust case, and the European parliament late last year even called for a breakup.
Asked about his recent trip to North Korea, Schmidt said the country has many Internet connections through data phones, but there is no roaming and web usage is “heavily supervised.” Schmidt said “it’s very much surveillance of use,” which he said was not good for the country and others.
Sandberg and Schmidt lauded the Internet as an important way to give more people in the world a voice. Currently, only 40 percent of people have Internet access, the Facebook COO said, adding that any growth in reach helps extend people’s voice and increase economic opportunity. “I’m a huge optimist,” she said about her outlook for the industry. “Imagine what we can do” once the world gets to 50 percent, 60 percent and more in terms of Internet penetration.
Schmidt similarly said that broadband can address governance issues, information needs, personal issues, women empowerment needs and education issues. “The Internet is the greatest empowerment of citizens … in many years,” he said. “Suddenly citizens have a voice, they can be heard.”
During another technology panel at the World Economic Forum on Thursday, Yahoo CEO Marissa Mayer, Liberty Global CEO Mike Fries and others answered questions on the need to regulate privacy standards on the Internet and for tech companies following the Snowden case, the Sony hack and the like.
Mayer said that the personalized Internet “is a better Internet,” emphasizing: “We don’t sell your personal data … We don’t transfer your personal data to third parties.” She said users own their data and need to have control, adding that people give up data to the government for tax assessment, social services and other purposes.
Both executives said transparency was important to make sure users know privacy standards and the like.
Gunther Oettinger, a conservative German politician serving as the European Union’s commissioner for digital economy and society, said on the panel that “we need a convincing global understanding, we need a UN agency for data protection and security.” Asked what form that “understanding” should have, he said he was looking for “clear, pragmatic, market-based regulation.” Explained Oettinger: “It’s a public-private partnership.”
Fries said such a solution was likely not to happen in the near term, given the size of the EU. “I think it is going to take several years,” he said, adding that some countries’ parliaments would likely take a stab at it.
But he warned that a joint solution would make more sense. “We don’t want Germany to have its own Internet,” Fries said. “Some countries may build their own Internets” and “balkanize” the web, he warned.
Mayer said on the issue of regulation: “I like Tim’s idea better of the beneficent marketplace.” She spoke of fellow panelist and computer specialist Tim Berners-Lee, known as the inventor of the World Wide Web.
Asked how Yahoo stores and handles client records, she said the online giant “changed the way we store and communicate data” after Snowden and also changed encryptions between data centers. And the company protects users through encryption methods, she added. Mayer said that trust and confidence of Yahoo users has rebounded since.
Mayer was also asked what happens if a government asks for a user’s data, a question that has new significance after the recent terrorist attacks in Paris, which have led some to call for increased surveillance powers of the Internet for governments. Mayer said Yahoo always assesses if such a request is reasonable. “We have a very good track record for standing up to what’s not reasonable,” she said.