Aug 14, 2016 01:12 AM
Back to the Drawing Board for Physics?
http://www.theatlantic.com/science/archi...cs/495260/
EXCERPT: Physicists at the Large Hadron Collider (LHC) in Europe have explored the properties of nature at higher energies than ever before, and they have found something profound: nothing new. It’s perhaps the one thing that no one predicted 30 years ago when the project was first conceived.
The infamous “diphoton bump” that arose in data plots in December has disappeared, indicating that it was a fleeting statistical fluctuation rather than a revolutionary new fundamental particle. And in fact, the machine’s collisions have so far conjured up no particles at all beyond those catalogued in the long-reigning but incomplete “Standard Model” of particle physics. In the collision debris, physicists have found no particles that could comprise dark matter, no siblings or cousins of the Higgs boson, no sign of extra dimensions, no leptoquarks—and above all, none of the desperately sought supersymmetry particles that would round out equations and satisfy “naturalness,” a deep principle about how the laws of nature ought to work.
“It’s striking that we’ve thought about these things for 30 years and we have not made one correct prediction that they have seen,” said Nima Arkani-Hamed, a professor of physics at the Institute for Advanced Study in Princeton, N.J. [...] The lack of new physics deepens a crisis that started in 2012 during the LHC’s first run, when it became clear that its 8-TeV collisions would not generate any new physics beyond the Standard Model. (The Higgs boson, discovered that year, was the Standard Model’s final puzzle piece, rather than an extension of it.) A white-knight particle could still show up later this year or next year, or, as statistics accrue over a longer time scale, subtle surprises in the behavior of the known particles could indirectly hint at new physics. But theorists are increasingly bracing themselves for their “nightmare scenario,” in which the LHC offers no path at all toward a more complete theory of nature.
Some theorists argue that the time has already come for the whole field to start reckoning with the message of the null results. The absence of new particles almost certainly means that the laws of physics are not natural in the way physicists long assumed they are. “Naturalness is so well-motivated,” Sundrum said, “that its actual absence is a major discovery.”
[...] Many particle theorists now acknowledge a long-looming possibility: that the mass of the Higgs boson is simply unnatural—its small value resulting from an accidental, fine-tuned cancellation in a cosmic game of tug-of-war—and that we observe such a peculiar property because our lives depend on it. In this scenario, there are many, many universes, each shaped by different chance combinations of effects. Out of all these universes, only the ones with accidentally lightweight Higgs bosons will allow atoms to form and thus give rise to living beings. But this “anthropic” argument is widely disliked for being seemingly untestable.
[...] There’s still hope that new physics will show up. But discovering nothing, in Spiropulu’s view, is a discovery all the same—especially when it heralds the death of cherished ideas. “Experimentalists have no religion,” she said. Some theorists agree. Talk of disappointment is “crazy talk,” Arkani-Hamed said. “It’s actually nature! We’re learning the answer! These 6,000 people are busting their butts and you’re pouting like a little kid because you didn’t get the lollipop you wanted?”
A Unified Theory of Randomness
https://www.quantamagazine.org/20160802-...andomness/
EXCERPT: [...] Beyond the one-dimensional random walk, there are many other kinds of random shapes. There are varieties of random paths, random two-dimensional surfaces, random growth models that approximate, for example, the way a lichen spreads on a rock. All of these shapes emerge naturally in the physical world, yet until recently they’ve existed beyond the boundaries of rigorous mathematical thought. Given a large collection of random paths or random two-dimensional shapes, mathematicians would have been at a loss to say much about what these random objects shared in common.
Yet in work over the past few years, Sheffield and his frequent collaborator, Jason Miller, a professor at the University of Cambridge, have shown that these random shapes can be categorized into various classes, that these classes have distinct properties of their own, and that some kinds of random objects have surprisingly clear connections with other kinds of random objects. Their work forms the beginning of a unified theory of geometric randomness. “You take the most natural objects — trees, paths, surfaces — and you show they’re all related to each other,” Sheffield said. “And once you have these relationships, you can prove all sorts of new theorems you couldn’t prove before....”
http://www.theatlantic.com/science/archi...cs/495260/
EXCERPT: Physicists at the Large Hadron Collider (LHC) in Europe have explored the properties of nature at higher energies than ever before, and they have found something profound: nothing new. It’s perhaps the one thing that no one predicted 30 years ago when the project was first conceived.
The infamous “diphoton bump” that arose in data plots in December has disappeared, indicating that it was a fleeting statistical fluctuation rather than a revolutionary new fundamental particle. And in fact, the machine’s collisions have so far conjured up no particles at all beyond those catalogued in the long-reigning but incomplete “Standard Model” of particle physics. In the collision debris, physicists have found no particles that could comprise dark matter, no siblings or cousins of the Higgs boson, no sign of extra dimensions, no leptoquarks—and above all, none of the desperately sought supersymmetry particles that would round out equations and satisfy “naturalness,” a deep principle about how the laws of nature ought to work.
“It’s striking that we’ve thought about these things for 30 years and we have not made one correct prediction that they have seen,” said Nima Arkani-Hamed, a professor of physics at the Institute for Advanced Study in Princeton, N.J. [...] The lack of new physics deepens a crisis that started in 2012 during the LHC’s first run, when it became clear that its 8-TeV collisions would not generate any new physics beyond the Standard Model. (The Higgs boson, discovered that year, was the Standard Model’s final puzzle piece, rather than an extension of it.) A white-knight particle could still show up later this year or next year, or, as statistics accrue over a longer time scale, subtle surprises in the behavior of the known particles could indirectly hint at new physics. But theorists are increasingly bracing themselves for their “nightmare scenario,” in which the LHC offers no path at all toward a more complete theory of nature.
Some theorists argue that the time has already come for the whole field to start reckoning with the message of the null results. The absence of new particles almost certainly means that the laws of physics are not natural in the way physicists long assumed they are. “Naturalness is so well-motivated,” Sundrum said, “that its actual absence is a major discovery.”
[...] Many particle theorists now acknowledge a long-looming possibility: that the mass of the Higgs boson is simply unnatural—its small value resulting from an accidental, fine-tuned cancellation in a cosmic game of tug-of-war—and that we observe such a peculiar property because our lives depend on it. In this scenario, there are many, many universes, each shaped by different chance combinations of effects. Out of all these universes, only the ones with accidentally lightweight Higgs bosons will allow atoms to form and thus give rise to living beings. But this “anthropic” argument is widely disliked for being seemingly untestable.
[...] There’s still hope that new physics will show up. But discovering nothing, in Spiropulu’s view, is a discovery all the same—especially when it heralds the death of cherished ideas. “Experimentalists have no religion,” she said. Some theorists agree. Talk of disappointment is “crazy talk,” Arkani-Hamed said. “It’s actually nature! We’re learning the answer! These 6,000 people are busting their butts and you’re pouting like a little kid because you didn’t get the lollipop you wanted?”
A Unified Theory of Randomness
https://www.quantamagazine.org/20160802-...andomness/
EXCERPT: [...] Beyond the one-dimensional random walk, there are many other kinds of random shapes. There are varieties of random paths, random two-dimensional surfaces, random growth models that approximate, for example, the way a lichen spreads on a rock. All of these shapes emerge naturally in the physical world, yet until recently they’ve existed beyond the boundaries of rigorous mathematical thought. Given a large collection of random paths or random two-dimensional shapes, mathematicians would have been at a loss to say much about what these random objects shared in common.
Yet in work over the past few years, Sheffield and his frequent collaborator, Jason Miller, a professor at the University of Cambridge, have shown that these random shapes can be categorized into various classes, that these classes have distinct properties of their own, and that some kinds of random objects have surprisingly clear connections with other kinds of random objects. Their work forms the beginning of a unified theory of geometric randomness. “You take the most natural objects — trees, paths, surfaces — and you show they’re all related to each other,” Sheffield said. “And once you have these relationships, you can prove all sorts of new theorems you couldn’t prove before....”
