Amplituhedron May Shape the Future of Physics

This multidimensional shape can simplify certain quantum equations — and possibly also revolutionize physics.

Physicists have long struggled to understand exactly what happens after subatomic particles collide. For decades, the best tool involved basic sketches (called Feynman diagrams) of each possible result. For all but the simplest scenarios, this method fills pages with drawings and equations. 

A new computational insight in 2004 dramatically reduced the amount of paper required to describe a collision, and these new formulas combined multitudes of Feynman diagrams into a single mess of math. Last year, Princeton physicist Nima Arkani-Hamed was analyzing the formulas in search of a better way to simplify these quantum calculations. Using only pen and paper, he discovered a new kind of geometric shape called an amplituhedron — one that hints at a new way of seeing the universe.

Arkani-Hamed noticed the formula could be rearranged and still yield the same answer. Like paleontologists brushing away dirt to reveal a fossil, he and his colleagues found the pieces of a shape within the math — pieces that together form a multidimensional amplituhedron. The shape’s dimensions — length, width, height and other parameters (hence “multidimensional”) — represent information about the colliding particles, and the equation describing its volume also describes the particles that emerge from the collision. 

This result, the volume, is a single term that fits on a space the size of a napkin.

Unlike the older methods for exploring particle collisions, the amplituhedron is not rooted in a world where a particle starts in one place and time before moving to the next location and moment. That is, the shape does not exist in space-time — it does not rely on a conception of the universe that theoretical physicists suspect might be incorrect. (When they try to knit together large-scale and small-scale forces, such as gravity and those that hold atoms together, the assumption of space-time leads to mathematical inconsistencies, a clue that something’s amiss with current assumptions about the universe.) 

“We’ve known for decades that space-time is doomed,” says Arkani-Hamed. “We know it is not there in the next version of physics.” Though the collisions described by the amplituhedron still occur in space-time, the object itself is outside it, providing a possible way to imagine a world not woven of this fabric.

The new shape is intriguing, says physicist Lance Dixon, a pioneer in the field of particle collisions, but he cautions that so far it can only describe particle collisions within a simplified version of quantum theory — the results don’t yet translate to the real world. Arkani-Hamed acknowledges it is a “baby example”; he calls it “step zero” in the journey to create a new kind of physics — a project on par with the discovery of the probabilistic particle collisions themselves. 

For now, the amplituhedron offers a hint of what this strange new world could look like.

For years, health professionals have been urging better nutrition and more exercise for children. Are we finally listening?

TOP 100 STORIES OF 2013

#9	Childhood Obesity Reversed

For years, health professionals have been urging better nutrition and more exercise for children. Are we finally listening?

By Jeff Wheelwright|Tuesday, January 07, 2014

RELATED TAGS: OBESITY, FAMILY HEALTH

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Public health officials call it an epidemic. The American Medical Association calls it a disease. During the past 30 years, obesity rates in the U.S. have more than doubled among adults (to 35 percent) and tripled among children and adolescents (to 17 percent). The problem seemed unstoppable — until this year. 

For the first time in decades, reported the Centers for Disease Control and Prevention (CDC), obesity rates declined among low-income preschool children, a particularly vulnerable demographic group. No magic diet was involved: This public health success seems to be the result of promoting healthier foods and physical activity. 

Between 2008 and 2011, the CDC measured the weights and heights of about 12 million children between the ages of 2 and 4 in 40 states, two territories and the District of Columbia. The preschoolers were on the rolls of federal nutrition programs, including the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC), which provides dietary counseling and food vouchers to low-income mothers. 

In 18 states, obesity rates declined slightly. Three states showed increases; the remaining 19 had no change from the prior survey. 

This small change could have big benefits down the road. Young children’s weight predicts their future health, says epidemiologist Ashleigh May, the lead author of the CDC report: “If they’re obese at this age, they’re five times as likely to become obese as adults.” Overweight children can develop high blood pressure and high blood sugar, which raises their risk of cardiovascular disease and diabetes when they grow up.

Four years ago, WIC revised its list of approved groceries to emphasize fruits and vegetables — one possible cause for the turnaround. More women are now breast-feeding, and breast-fed babies are more likely to be at a healthy weight. 

The CDC also credits public awareness programs like “Let’s Move,” championed by first lady Michelle Obama, that promote healthy eating and exercise in day care centers and among child care providers. “We were expecting spotty progress, but this [decline] was widespread,” Let’s Move Executive Director Sam Kass says.

A White House task force calls for childhood obesity rates to fall to 5 percent by 2030. Is it a reasonable goal? 

“All the public health campaigns in this country required concerted efforts over many years,” says pediatrician David Ludwig, director of the New Balance Foundation Obesity Prevention Center at Boston Children’s Hospital. He cites drives to reduce traffic fatalities and curb tobacco use. “We have every reason to hope for an eventual
victory.”