Physicist tests theories of dark energy by mimicking the vacuum of space

Besides the atoms that make up our bodies and all of the objects we encounter in everyday life, the universe also contains mysterious dark matter and dark energy. The latter, which causes galaxies to accelerate away from one another, constitutes the majority of the universe’s energy and mass.

Ever since dark energy was discovered in 1998, scientists have been proposing theories to explain it—one is that dark energy produces a force that can be measured only where space has a very low density, like the regions between galaxies.

Paul Hamilton, a Univ. of California, Los Angeles (UCLA) assistant professor of physics and astronomy, reproduced the low-density conditions of space to precisely measure this force. His findings, which helped to reveal how strongly dark energy interacts with normal matter, appear online in Science.

Hamilton’s research focuses on the search for specific types of dark energy fields known as “chameleon fields,” which exhibit a force whose strength depends on the density of their surrounding environment. This force, if it were proven to exist, would be an example of a so-called “fifth force” beyond the four known forces of gravity, electromagnetism, and the strong and weak forces acting within atoms.

Carbon number crunching

A booming economy and population led China to emerge in 2006 as the global leader in fossil-fuel carbon emissions, a distinction it still maintains. But exactly how much carbon China releases has been a topic of debate, with recent estimates varying by as much as 15%.

“There’s great scrutiny of Chinese emissions now that they are the world’s largest fossil-fuel emitter,” said Tom Boden from the U.S. Dept. of Energy (DOE)’s Oak Ridge National Laboratory (ORNL). “Their economy has grown at such a fast rate, so naturally a lot of attention has turned to their emission estimates.”

As director of the Carbon Dioxide Information Analysis Center (CDIAC) at ORNL, Boden has been tracking the world’s carbon emissions for the past 25 years. CDIAC’s annual inventory of carbon released from fossil fuels by country has become a benchmark dataset for climate change scientists and policymakers.

Boden, ORNL’s Bob Andres, and Appalachian State Univ.’s Gregg Marland, a former ORNL scientist, recently lent their emissions data expertise to a new Nature study that reevaluated China’s emissions from 2000 to 2013. The study, led by Zhu Liu of Harvard Univ., illustrates how carbon emissions estimates take into account a complex set of variables.