Measuring the Mysterious ‘Dark’ Force

http://www.nytimes.com/2008/12/17/science/space/17darkside.html

Measuring the Mysterious ‘Dark’ Force
By DENNIS OVERBYE
Published: December 16, 2008

Measurements of the lack of growth of galaxy clusters over the last five billion years put astronomers one step closer, they say, toward narrowing the possible explanations of dark energy, the mysterious force that is speeding up the universe.

Physicists denote the virulence of dark energy by a number called w, the equation of state. From the stifling of cluster growth, Dr. Alexey Vikhlinin’s multinational team derived a value of w of about minus 1.14, plus or minus 0.21. That is within shooting range of the magic value for the cosmological constant of minus 1.

The constraints on dark energy tighten considerably when the cluster measurements are combined with the supernova measurements and others, including observations of the cosmic microwaves left over from the Big Bang, in which the seeds of cosmic structures like galaxy clusters can be seen, yielding a w of minus 0.991, plus or minus .045.

That looks like an improvement of a factor of 2 on the uncertainty charts that dark energy specialists show to one another in meetings and papers, but critics caution that combining disparate types of measurements can result in an artificially small error that masks underlying uncertainties. Astronomers, for example, still do not have a good theory to explain how their standard candles, supernovas, explode, and theories of cluster growth depend on assumptions about the nature of the dark matter in the universe and the nature of the original fluctuations that give birth to them.

Even the improved error bars still leave a lot of wiggle room for other theories of dark energy, and some astronomers worry that the measurements even from the upcoming dark energy satellite will never get accurate enough to prove or disprove the cosmological constant.

Paul Steinhardt of Princeton University pointed out that the uncertainties in the cluster results are larger if you consider the possibility that w could vary with cosmic time, “which is what you should do if you are trying to test the idea that the dark energy is not a cosmological constant,” he said in an e-mail message.

But the fact that the answer from clusters came out so close to the cosmological constant is a vote of confidence for Einstein’s general relativity, said William Forman of Harvard, a member of Dr. Vikhlinin’s team. “This is a test that general relativity could have failed,” he said.

Indeed, several theorists said the future now looked dim for alternative theories of gravity, in particular a variant from string theory, which incorporates extra dimensions and which predicts enhanced growth of structures like galaxy clusters. David Spergel, a theorist at Princeton University, said that although quantitative tests had not yet been done with the new data, “I suspect that it rules out those models.”

Dr. Vikhlinin lamented that there were not yet very many such theories to knock down yet, but there were sure to be more on the table soon. “The field has just started, I think,” he said.

Paul Krugman Wins Nobel Economics Prize

Robalini's Note: In many ways, this has more long-term impact than anything which will happen in November. With Stiglitz having already won in 2001, all that is needed is Robert Reich winning to make a liberal economist hat trick. Just as important, we're starting to see a rejection of the Milton Friedman cult and the University of Chicago school of thought.

http://www.bloomberg.com/apps/news?pid=20601087&sid=axpy67IVqPj8

Princeton's Paul Krugman Wins Nobel Economics Prize
By Benedikt Kammel

Oct. 13 (Bloomberg) -- Princeton University professor and New York Times columnist Paul Krugman won the Nobel Prize in economics for his work on trade theory.

Krugman, 55, received the prize ``for his analysis of trade patterns and location of economic activity,'' said the Royal Swedish Academy of Sciences, which selects the winners. His work explained how economies of scale influence trade and urbanization.

``It's a total surprise,'' Krugman said in a telephone interview.

Krugman gained his reputation in economics by contributing to strategic trade theory, contending that countries could steal a march on other nations by subsidizing strategic industries. He has found broader fame with his newspaper columns that regularly criticize President George W. Bush's policies.

In an interview with Bloomberg Television on Oct. 10, Krugman said the current financial turmoil had similarities with the Great Depression. ``The parallels are stronger than I thought they would be,'' he said. ``We developed a financial system that is out of control. The only things people want to buy are T-bills and water.''

The Nobel laureate said today he saw little danger of a move toward protectionism in the U.S., no matter which party wins in next month's elections.

Protectionism

``There may be a standstill, or slowdown at least, on new trade agreements, but I find reversal on trade agreements implausible,'' he said in remarks via telephone to a group of reporters in Stockholm. ``Full-scale protectionism I don't see.''

He has argued the benefits of subsidies are generally marginal. He has also been praised for his work on the development of industrial clusters and his equations on the impact of economic shocks on the current account, exchange rates and capital flows.

In 1991, he was awarded the John Bates Clark Medal by the American Economic Association, which is awarded to the best economist under the age of 40.

Krugman was born in Long Island and studied economics at Yale University. He obtained a Ph.D. from the Massachusetts Institute of Technology in 1977 before joining Princeton University. From 1982 to 1983 he served on the White House Council of Economic Advisers, during the presidency of Ronald Reagan. He has published a series of books and his ability to turn complicated economic theory into understandable prose led to him write an opinion column for the New York Times for the past eight years.

Previous Winners

Alfred Nobel, the Swede who invented dynamite, in his will in 1896 established awards for achievements in physics, chemistry, medicine, peace and literature. The economics prize was set up by Sweden's central bank in 1968. Former winners include Milton Friedman, Amartya Sen and Friedrich August von Hayek.

The award's official name is ``The Bank of Sweden Prize in Economic Sciences in Memory of Alfred Nobel.'' The prize consists of 10 million Swedish kronor ($1.41 million), a gold medal and a diploma.

To contact the reporters on this story: Rich Miller in Washington o rmiller28@bloomberg.net; Simon Kennedy in Washington at skennedy4@bloomberg.net