At Ten, Dark Energy "Most Profound Problem" in Physics

Victoria Jaggard in Baltimore, Maryland

National Geographic News

May 16, 2008
What goes up must come down. Few on Earth would argue with the fundamental law of gravity.

But ten years ago this month the Astronomical Journal accepted a paper for publication that revealed there is a dark side of the force.

For decades physicists were convinced that gravity should be causing the expansion rate of the universe to slow.

"When I throw my keys up in the air, the gravity of the Earth makes them slow down and return to me," said Mario Livio, a theoretical physicist at the Space Telescope Science Institute (STScI) in Baltimore, Maryland.

But the study, along with an independent work released later the same year, showed that the expansion rate is actually speeding up.

This observation, Livio said, is as if "the keys suddenly went straight up toward the ceiling."

Scientists attribute the phenomenon to dark energy, a force that repels gravity. Even more surprising, measurements show that dark energy accounts for about 74 percent of the substance of the universe.

A decade later, a new suite of experiments may pin down the properties of dark energy and solve what some experts are calling "the most profound problem" in modern physics.

"This is game-changing science," Michael Turner, a cosmologist at the University of Chicago, told a packed auditorium during the Decade of Dark Energy Symposium held last week at STScI.

"We've gone from establishing the phenomenon to probing the underlying cause," he said. "We're not anywhere near the point where it's time to give dark energy a rest."

Energy in a Vacuum

So far, one of the biggest challenges for dark energy researchers is marrying observations to theory.

Biomedical Technology Has a Home at Livermore

INNOVATIVE science and the exploration of advanced technologies for biomedical applications are needed to improve human health worldwide and to address the national need of affordable health care for an aging population. When facing these challenges, biomedical research institutions benefit from a variety of research and development activities at Department of Energy (DOE) laboratories, which are sources of special capabilities and expertise. However, at times, the question arises, “Why Lawrence Livermore, a national security laboratory?”

The ties between our national security work and human health have deep roots in the Laboratory’s history. In 1963, Livermore formed a biomedical research program to better understand the effects of ionizing radiation on biological systems—an important issue for worker safety within the nuclear weapons complex and for the resettlement efforts in the Marshall Islands following the end of atmospheric nuclear testing. Research efforts focused on chromosome damage soon led to the development of chromosome sorting technology here and at Los Alamos National Laboratory, culminating in the birth of the Human Genome Project. Today, we are a partner in DOE’s Joint Genome Institute and a developer of advanced biological agent detectors and pathogen signatures used for homeland security and health applications.

In addition, the ties between developing technologies for national security and for biomedical applications are numerous. Livermore’s expertise in accelerator technology and radiography stems from our hydrodynamic testing. Radiography is also important for the nondestructive evaluation of weapons as part of stockpile surveillance programs. We are now working with a licensee to develop the first compact proton therapy system, an accelerator that would fit in any major cancer center at a fifth the cost of larger machines in use today. The accelerator is based on a technology breakthrough made at Livermore and is a result of our continuing interest in compact accelerators for future hydrodynamic testing at the Nevada Test Site.

Laser technologies also bridge national security and biomedical applications. Adaptive optics are key to the design and construction of the National Ignition Facility, and a microelectromechanical adaptive optics system is behind a new ophthalmoscope that won a Laboratory team an R&D 100 Award last year. The ophthalmoscope sharpens images of retinal cell layers, allowing clinicians to diagnose macular degeneration and other retinal diseases much earlier than was previously possible. Lasers also are important components in advanced diagnostics for many nondestructive evaluation applications, and they are the reason for our collaboration with the University of California at Davis’s Center for Biophotonics, Science and Technology—one of our many partnerships with Davis in medical technologies and cancer research.

Materials science research for national security and broader applications is also a Laboratory strength. Recent research includes work on shape-memory polymers (SMPs)—a class of “smart” materials that, as a result of an external stimulus, can change from a deformed shape back to their original shape. SMPs are increasingly used in medical devices, aerospace technologies, and textiles, where their dynamic response can change material performance. They are both inexpensive and easy to manufacture.

The article Shaping the Future of Aneurysm Treatments describes an application using SMPs to improve the treatment of aneurysms. The research team has synthesized new materials with superior properties over those commercially available today and demonstrated biocompatibility and utility. Remarkable progress has been made by combining theory, experiment, and simulation. We look forward to seeing such a promising technology adopted by the medical industry.

This multidisciplinary project—and the application of our technological advances to a broad range of important national needs—exemplifies the mission of the Laboratory and the creativity of our scientists and engineers.

Source
Lawrence Livermore National Laboratory
Operated by Lawrence Livermore National Security, LLC, for the
U.S. Department of Energy’s National Nuclear Security Administration

The Laboratory in the News

Global warming threatens West’s water resources

Water flow in the western U.S. has decreased for the last 20 to 30 years, but scientists have never understood why. Benjamin Santer of Livermore’s Program for Climate Model Diagnosis and Intercomparison and collaborators from the Scripps Institution of Oceanography have for the first time pinpointed humans as the cause of diminishing water flow on a regional scale. By looking at air temperature, river flow, and snowpack during the last 50 years, the team determined that the human-induced increase in greenhouse gases has seriously affected the water supply in the western U.S. “The water flow decrease is a result of temperature change,” says Scripps colleague Tim Barnett, “and that temperature change is caused by us.”

Santer and Barnett presented the research at the American Geophysical Union Meeting in December 2007. The team scaled down global climate models to a regional level and compared the results to their observations. The researchers found they could use the same models to predict the effects of the increase in greenhouse gases on the western U.S. in the future. By 2040, most of the snowpack in the Sierras and Colorado Rockies would melt by April 1 of each year because of rising air temperatures, causing a shift in river flows. With the existing greenhouse gas in the atmosphere, Earth will continue to warm for the next 80 to 100 years. “We are headed for a water crisis in the western United States, and it has already started,” says Barnett.
Contact: Benjamin Santer (925) 422-2486 (santer1@llnl.gov).

Human activities may shape California climate

Through research funded by the California Energy Commission, scientists from the Laboratory, the University of California at Merced, and the National Center for Atmospheric Research found that temperatures in California from 1915 to 2000 have increased by 1.16°C (2.1°F) statewide. The research, which appeared in the December 19, 2007, online edition of Climatic Change, also suggests that the warming may be related to human activities.

The team used data from up to eight observational records and found that warming has been fastest in late winter and early spring. “The trends in daily minimum and maximum temperatures over the last 50 and 85 years are inconsistent with current model-based estimates of natural internal climate variability,” says Livermore’s Céline Bonfils. “It’s pretty clear the increases are not the result of just natural causes. External factors such as greenhouse gases and urbanization come into play.” However, current climate models have not been effective in explaining California’s summertime trend, where warming mainly occurs at night. Previous research by the team indicates that large-scale irrigation in California has had a cooling effect on summer daytime temperatures, which may have counteracted warming from mounting greenhouse gases and urbanization. If this hypothesis is verified, the acceleration of carbon dioxide emissions combined with a leveling of irrigation may result in a rapid summertime warming in the Central Valley in the near future.

Researchers suggest that greenhouse warming will continue to influence climate and may have significant societal impacts in California. Benjamin Santer, also a member of the Livermore team, says, “Our study represents a credible first step toward identifying the effects of human activities on California’s climate.”
Contact: Céline Bonfils (925) 423-9923 (bonfils2@llnl.gov).

Stardust samples reveal unexpected results

Laboratory scientists, working with collaborators from other scientific and academic institutions, have unveiled new research on the dust collected from Comet Wild 2 during the Stardust mission. In a surprising turn of events, the research failed to find the primitive materials that had been thought to abound in comets. Rather, the dust from this particular comet formed very close to the young Sun and is more like material in asteroids. The research appeared in the January 25, 2008, edition of Science.

Researchers used Livermore’s aberration-corrected, monochromated, scanning transmission electron microscope known as SuperSTEM to analyze the Stardust samples. The samples were compared to interplanetary dust particles (IDPs) gathered from Earth’s stratosphere. Believed to be cometary dust, these IDPs contain the most primitive starting materials from which the planets in the solar system formed. Researchers were particularly interested in identifying in the Wild 2 dust two silicate materials unique to the IDPs, GEMS (glass with embedded metal and sulfides) and crystalline silicate enstatite (a rock-forming mineral). The team found only a single sliverlike whisker of enstatite, and it was similar to material in asteroids, not IDPs. Objects similar to GEMS were found, but the team determined they were created during the high-speed impact with Wild 2 dust.

The research emphasizes the continuum between asteroids and comets. “Wild 2 doesn’t match our idealized picture of a primitive comet made of ancient, unaltered material,” says Livermore scientist Hope Ishii. “The Stardust mission was a real success because without it, we never would have learned these things about our solar system. The returned sample is enabling us to continue to unravel how our solar system formed and evolved.”

Contact: Hope Ishii (925) 422-7927 (ishii2@llnl.gov).