NASA Delays “Wfirst” Space-Based Search for Dark Energy -Can Europe & Earth-Based Solutions Take Up the Slack?

Dark_energy_cluster_2.jpg An ambitious $1.6 billion spacecraft, known as Wfirst, for Wide-Field Infrared Survey Telescope, that would investigate the mysterious force that is apparently accelerating the expansion of the universe — and search out planets around other stars, might have to be postponed for a decade, NASA reported today because of cost overruns and mismanagement on a separate project, the James Webb Space Telescope that will search out the first stars and galaxies to have formed in the universe, but is not designed to search for dark energy.

Last summer the National Academy of Sciences gave highest priority among big space projects in the coming decade to the satellite telescope that would take precise measure of dark energy and also search for exo planets

“How many things can we do in our lifetime that will excite a generation of scientists?” asked Saul Perlmutter, an astronomer at the University of California, Berkeley, who is one of dark energy’s discoverers according to a report in the New York Times. There is a sense, he added, “that we’re starting to give up leadership in these important areas in fundamental physics.”

To compensate for the delay, NASA has proposed buying a 20 percent share in a European dark-energy mission known as Euclid that could fly as soon as 2018. In return, NASA would ask for a similar investment by Europe in Wfirst. Dr. Perlmutter told the New York Times: “most of us think it is hard to imagine if we do Euclid now that we will do a dark-energy mission then.” Most of
the nation's prestigous scientists see the USA conceeding leadership to Europe.

The discovery a decade ago that the universe is speeding up, in defiance of common sense or cosmic gravity, has thrown into doubt notions about the fate of the universe and of life within it, not to mention gravity and even the nature of the laws of physics. “We’re looking at a tug-of-war with dark energy and gravity trying to expand or collapse the universe.” John Carlstrom, South Pole astronomer and University of Chicago astrophysicist.

Carlstrom is a member of the team using an Earth-based solution in the search for dark energy: a big telescope, as high as a seven-story building, with a main mirror measuring 32 1/2 feet across was built at the Amundsen-Scott Station in the Antarctica  looming over a barren plain of ice that gets colder than anywhere else on the planet. The South Pole Telescope (SPT), a microwave telescope, has been in use since February 16, 2007. More about the SPT below…

Physicists have one ready-made explanation for the acceleration of the universe, according to the New York Times, "but it is a cure that many of them think is worse than the disease: a fudge factor invented by Einstein in 1917 called the cosmological constant. He suggested, and quantum theory has subsequently confirmed, that empty space could exert a repulsive force, blowing things apart. But the best calculations predict an effect 10 to the exponent of 120 times greater than what astronomers have measured, causing physicists to metaphorically tear their hair out and mutter about multiple universes."

The astronomers who made this discovery were using the exploding stars known as Type 1a supernovae as cosmic metric to measure the expansion rate of the universe. Since then, according the the Times article, other tools have emerged by which astronomers can also gauge dark energy by how it retards the growth of galaxies and other structures in the universe. So far the observations are not definitive; more precise measurements, many of which can only be done from space, are needed.

One big problem with Europe's Euclid mission is that it does not include observations of supernovae, the technique by which dark energy was discovered. Nor summarized the New York Times, does the United States play a leadership role.

The STP at the far end of the world was built so scientists can search for clues to the mysterious phenomenon called dark energy, which makes the expansion of the universe accelerate. Albert Einstein's famous "cosmological constant," mentioned above as one possibility for the dark energy, also will come under the telescope's scrutiny.

The "gravity" of dark energy is repulsive. It pushes the universe apart and overwhelms ordinary gravity, the attractive force exerted by all matter in the universe. Dark energy is invisible, but astronomers will be able to see its influence on clusters of galaxies that formed within the last few billion years.

"With the South Pole Telescope we can look at when galaxy clusters formed and how they formed. That is critically dependent on the nature of the dark energy, this elusive component of the universe," said Carlstrom, who heads the project. "We've only known about dark energy for a few years. No one really knows what it is."

"One of our main goals is to figure out what dark energy is," said center Director Bruce Winstein, the University's Samuel K. Allison Distinguished Service Professor in Physics. "Is it a cosmological constant or is it dynamical? The South Pole Telescope holds the promise to give us a lot of new, valuable information on this.".

First described a decade ago, dark energy is a mysterious force so powerful that it will decide the fate of the universe. Having already overruled the laws of gravity, it is pushing galaxies away from one another, causing the universe to expand at an ever faster rate.

Though dark energy is believed to account for 70 percent of the universe's mass, it is invisible and virtually undetectable. Nobody knows what it is, where it is or how it behaves.

Solving the mystery of dark energy is would explain the history and future of the universe and generate new understanding of physical laws that, applied to human invention, almost certainly will change the way we live — just as breakthroughs in quantum mechanics brought us the computer chip.

Swinging its massive mirror skyward, the South Pole Telescope (SPT) searches the southern polar heavens for shreds of evidence of the elusive stuff. Controlled remotely from the University of Chicago, the $19.2 million telescope quickly succeeded in its first mission: finding unknown galaxy clusters, clues to the emergence of dark energy.

The cold, dry atmosphere above the South Pole allows the SPT to more easily detect the cosmic microwave background radiation (CMB), the afterglow of the big bang, with minimal interference from water vapor. On the electromagnetic spectrum, the CMB falls somewhere between heat radiation and radio waves.

The CMB is largely uniform, but it contains tiny ripples of varying density and temperature. These ripples reflect the seeds that, through gravitational attraction, grew into the galaxies and galaxy clusters visible to astronomers in the sky today. One of the SPT’s first key science project was to study small variations in the CMB to determine if dark energy began to affect the formation of galaxy clusters by fighting against gravity over the last few billion years.

Galaxy clusters (image at top) are groups of galaxies, the largest celestial bodies that gravity can hold together. Our galaxy, the Milky Way, is in one of these clusters, which actually change with time.

The CMB allows astronomers to take snapshots of the infant universe, when it was only 400,000 years old. No stars or galaxies had yet formed. If dark energy changed the way the universe expanded, it would have left its “fingerprints” in the way that it forced galaxies apart over the deep history of time. Different causes would produce a different pattern in the formation of galaxy clusters as reflected in the distortion of the CMB.

According to one idea, dark energy could be Einstein’s cosmological constant: a steady force of nature operating at all times and in all places. Einstein introduced the cosmological constant into his theory of general relativity to accommodate a stationary universe, the dominant idea of the day. If Einstein’s idea is correct, scientists will find that dark energy was much less influential in the universe five billion years ago than it is today.

“Clusters weren’t around in the early universe. They took a long time to evolve,” Carlstrom said.

Another version of the dark energy theory, called quintessence, suggests a force that varies in time and space. Some scientists even suggest that there is no dark energy at all, and that gravity merely breaks down on vast intergalactic scales.

Scientists expect the telescope to detect tens of thousands, of galaxy clusters within a few years.

Casey Kazan.



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