NASA and the Department of Energy (DoE) initially asked the NRC to access projects in five physics/astronomy areas: dark energy, black holes, gravitational radiation, inflation of early universe, and Einstein’s gravitational theory. After a year of research and study the NRC group decided that dark energy had the greatest potential to produce the most scientific information.

The five cosmological missions, which would be included within the Beyond Einstein program—set to begin in 2009—include: (two astronomical observatories) Constellation-X and Interferometer Space Antenna (LISA); and (five probes) the Inflation Probe (IP), the Black Hole Finder Probe (BHFP), and the Joint Dark Energy Mission (JDEM).

The study group thought that LISA was the most important of the five missions; however, the JDEM mission was further along and should be pursued first.

In fact, co-chairperson for the NRC study Charles Kennel (professor at the University of California, San Diego, and director of the Environment and Sustainability Initiative) stated, “All of the mission areas in the Beyond Einstein program have the potential to fundamentally alter our understanding of the universe. But JDEM will provide direct insight into a key Beyond Einstein science question, and is the most technically feasible option for immediate development.”

Dark energy is a mysterious, only hypothetically known, force that permeates throughout the universe. It is a form of energy that is thought to increase the expansion of the universe. According to the standard model of cosmology, about 75% of the total mass-energy of the universe is supposedly made up of dark energy.

German American physicist Albert Einstein proposed the existence of dark energy when he included a lambda (his “cosmological constant”) into his equations for his theory of general relativity when he was trying to explain the stationary (neither contracting nor expanding) nature of the universe. To Einstein it was a force that worked against gravity to keep everything in the universe static (resistant from moving).

However, American astronomer Edwin Hubble later showed that the universe was expanding after he discovered what is now called the Hubble redshift—that is, light is redshifted, appears longer in wavelength than it should, because galaxies are moving away, and the amount of redshift is proportional to their distance away from Earth (what is called Hubble’s Law).

This discovery, put a damper on Einstein’s lambda and his static universe, and Einstein abandoned the concept. Einstein eventually said his lambda was one of his biggest blunders.

However, since the 1990s, cosmologists have found that the universe is not only expanding but its expansion is accelerating. They are now using Einstein’s lambda to help explain why this is happening.

Saul Perlmutter, professor of physics at UC-Berkeley, reacted to the decision to the NRC study by saying: “It's wonderful to know that NASA will be moving forward with this exciting project as a result of the committee's recommendation that JDEM be the first mission to fly. Each of the highly ranked Beyond Einstein projects will contribute greatly to our understanding of the universe, yet few questions are more fundamental or pressing than the mysterious nature of dark energy, which accounts for some three-quarters of the density of our universe -- but about which we know almost nothing."

The media press release is found at: http://www8.nationalacademies.org/onpinews/newsitem.aspx?RecordID=12006.


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