A proposed NASA mission to study a mysterious force thought to be accelerating the expansion of the universe should be the first in the agency's "Beyond Einstein" program to be developed and launched, the National Research Council recommended today.
Beyond Einstein is NASA's research roadmap for five proposed space missions set to begin in 2009 that will study areas in science that build on and extend the work of physicist Albert Einstein.
The missions include Constellation-X and the laser Interferometer Space Antenna (LISA), which will measure X-rays and look for hypothetical gravity waves, respectively, as well as the Inflation Probe (IP), the Black Hole Finder Probe (BHFP) and the Joint Dark Energy Mission (JDEM).
The National Research Council report recommended that JDEM be the first mission to be deployed since it is already in the prototype phase and will require less development than the other missions.
"All of the mission areas in the Beyond Einstein program have the potential to fundamentally alter our understanding of the universe," said committee co-chair Charles Kennel of the University of California, San Diego. "But JDEM will provide direct insight into a key Beyond Einstein science question, and it is the most technically feasible option for immediate development."
Dark energy is a mysterious force scientists think is speeding up the expansion of spacetime and constitutes some three-quarters of the density of the universe.
It was initially proposed by Einstein as a counterforce to the gravitational attraction of matter to explain why the universe appeared static, neither growing nor shrinking. But he later dismissed his idea as a mistake when observations by astronomer Edwin Hubble revealed the universe was in fact expanding.
Dark energy, which Einstein called lambda, was revived in the late 1990s when astronomers discovered that the universe was not only expanding, but expanding at an accelerated clip.
The report also recommended that LISA become the flagship mission of the program and that more money be funneled into the project because it could provide an entirely new way of observing the universe. However, the report committee believes that more testing is required before it launches. Specifically, the mission must await the results of the LISA Pathfinder mission in 2009 that will test some of the critical technologies to be used in the final LISA mission.
The report was sponsored by the U.S. Department of Defense and NASA. The Research Council is the principal operating agency of the National Academy of Sciences and the National Academy of Engineering.
Dark energy facts.
In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe.  Assuming the existence of dark energy is the most popular way to explain recent observations that the universe appears to be expanding at an accelerating rate. In the standard model of cosmology, dark energy currently accounts for almost three-quarters of the total mass-energy of the universe.
Two proposed forms for dark energy are the cosmological constant, a constant energy density filling space homogeneously, and scalar fields such as quintessence or moduli, dynamic fields whose energy density can vary in time and space. In fact contributions from scalar fields which are constant in space are usually also included in the cosmological constant. The cosmological constant is thought to arise from the vacuum energy. Scalar fields which do change in space are hard to distinguish from a cosmological constant, because the change may be extremely slow.
High-precision measurements of the expansion of the universe are required to understand how the speed of the expansion changes over time. The rate of expansion is parameterized by the cosmological equation of state. Measuring the equation of state of dark energy is one of the biggest efforts in observational cosmology today.
Adding the cosmological constant to cosmology's standard FLRW metric leads to the Lambda-CDM model, which has been referred to as the "standard model" of cosmology because of its precise agreement with observations.
Nature of Dark energy.
The exact nature of this dark energy is a matter of speculation. It is known to be very homogeneous, not very dense and is not known to interact through any of the fundamental forces other than gravity. Since it is not very dense-roughly 10−29 grams per cubic centimeter-it is hard to imagine experiments to detect it in the laboratory. Dark energy can only have such a profound impact on the universe, making up 70% of all energy, because it uniformly fills otherwise empty space. The two leading models are quintessence and the cosmological constant