Dark-energy fingerprints found in ancient radiation
16:53 15 July 2011 by Kate McAlpine
Only cat burglars can match the stealth of dark energy, credited with speeding up the universe's expansion over time, but now its fingerprints have been glimpsed in the universe's oldest radiation.
The strongest evidence for dark energy comes from supernovae, which suggest the universe is expanding faster now than in the past. But the force should also change the extent to which the cosmic microwave background (CMB), relic radiation from the big bang, is warped, or "lensed", by the gravity from distant galaxies and dark matter.
That's because the accelerating expansion of the universe should prevent the growth of very massive structures. "In a universe with no dark energy, massive objects would just keep growing, which results in more gravitational lensing," says Sudeep Das of the University of California, Berkeley.
Gravitational lensing is tough to pick out in the ancient radiation because the CMB contains random fluctuations. But Das and his colleagues have used a new type of mathematical analysis to reveal for the first time the distinctive distortions from gravitational lensing in the CMB.
Planck pending
The measurement, while not breaking any records for accuracy, bolsters the case for dark energy. "Because of dark energy's importance to both the future evolution of the universe and the foundation of physics, it is extremely important to find a variety of evidence that confirms its existence," says Stephen Boughn of Haverford College in Pennsylvania, who was not involved in the work.
Das's observations of the CMB were made with the Atacama Cosmology Telescope in Chile, but Europe's Planck satellite will soon return even more detailed measurements.
Applying the same mathematical technique to this Planck data could help astronomers better understand other important problems in cosmology. One outstanding question regards the mass of the neutrino, an elusive particle with a mass so small that it has yet to register in any measurement.
Smooth operator
Nevertheless, neutrinos ought to interact with the universe's mass on the largest scales: as these particles careen through the universe at near light-speed, they interact with ordinary matter and tend to smooth out variations in density. If the neutrinos are more massive, this effect is stronger, but restricted to shorter distances. By contrast, near-massless neutrinos aren't so forceful, but would show their effects over longer distances.
Since gravitational lensing of the CMB gives a measure of matter's tendency to clump together over a large range of distances, it can hint at the strength and scale of the smoothing. And this, in turn, will allow cosmologists to put a limit on the maximum possible mass of the neutrino.
Last year a team at University College London used the clustering of galaxies as a proxy for the clumping of matter, and their result put that mass at under 0.28 electronvolts, less than one-millionth the mass of an electron.
Gravitational lensing in the CMB could pin down the sum of the masses of the three types of neutrino with even greater accuracy.
Most people eating pasta might enjoy the taste or appreciate the texture of noodles cooked al dente.
Sander Huisman did, too — and then he wondered about what mathematical equation would describe the undulating shapes he was eating.
Mr. Huisman, a graduate student in physics at the University of Twente in the Netherlands, spends much of his days using Mathematica, a piece of software that solves complicated math problems and generates pretty pictures of the solutions.
“I play around with Mathematica a lot,” he said. “We were eating pasta, and I was wondering how easy these shapes would be recreated” with the software.
So that evening after dinner, Mr. Huisman figured out the five lines or so of Mathematica computer code that would generate the shape of the pasta he had been eating — gemelli, a helixlike twist — and a dozen others. “Most shapes are very easy to create indeed,” he said.
He posted one of them [ http://shuisman.com/?p=369 ] to his blog, thinking he would do a sort of mathematical-pasta-of-the-month for the next year. But he then forgot about them until someone asked for the recipes of the other pasta shapes, and he posted those to his blog [ http://shuisman.com/?p=1314 ], too.
Mr. Huisman, who studies fluid dynamics, is not the only who has been mathematically inspired by pasta. Several years ago, Christopher Tiee, then a teaching assistant for a vector calculus class at the University of California, San Diego, included in his notes a pop quiz asking students to match pasta shapes with the equations.
Meanwhile, in London, two architects, Marco Guarnieri and George L. Legendre, independently experienced a similar epiphany, also while eating pasta (spaghetti with garlic and olive oil, cooked by Mr. Guarnieri). Then Mr. Legendre went many steps further: He turned the idea into a 208-page book, “Pasta by Design [ http://www.thamesandhudson.com/9780500515808.html ],” released in September by Thames & Hudson, a British publisher specializing in art books.
“We were interested in, if you like, the amalgamation of mathematics and cooking tips — the profane, the sacred,” Mr. Legendre said. “I was actually speaking to someone in Paris last week who said, ‘This might have been a project by Dali.’ ”
The book classifies 92 types of pasta, organizing them into an evolutionlike family tree. For each, the book provides a mathematical equation, a mouthwatering picture and a paragraph of suggestions, like sauces to eat it with.
Mr. Legendre calls trenne, a pasta with the rigid angles of triangular tubes, a freak. “It’s a mirror universe where everything is pliant and groovy, and in that universe there’s someone that stands out, and it’s the boring-looking trenne with its sharp edges,” he said.
Mr. Legendre has even designed a new shape — ioli, named for his baby daughter — which looks like a spiral wrapped around itself, a tubelike Möbius strip.
“I thought it might be nice to have a pasta named after her,” he said.
He is looking to get about 100 pounds of pasta ioli manufactured, but that is still probably months away, because of the challenges of connecting the ends together.
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