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Posts Tagged ‘dark energy’

In a paper to be published in the International Journal of Modern Physics, available online now here, Dr. David Wiltshire proposes a modification of Einstein’s General Theory of Relativity which helps explain the enigma of dark energy. As Dr. Wiltshire puts it, “dark energy is revealed as a mis-identification of gravitational energy gradients and the resulting variance in clock rates.” As part of his modification he establishes what he calls the Cosmological Equivalence Principle which addresses the so-called Mach Principle, which is one of the things that got Einstein working on general relativity originally. Mach’s Principle is nicely summarized here, in essence it relates your local frame of reference to that of the stars.

In a paper to be published in the Astrophysical Journal, available online here, a team of astronomers have re-examined observations of spectra from quasars, coming to the conclusion that the mass ratio of the proton to electron, has not changed over the course of history of the universe going back almost 11 billion years. Remember that the further out in space we look, the further back in time we are looking. The significance of these findings is that there exist theories which address the nature of the so-called dark energy of the universe (the cause of the apparent accelerating expansion of the universe) which call for this fundamental constant to have changed over time. Apparently, this fundamental constant is really constant.

If you want an excellent review of the evidence for dark energy and the accelerating expansion of the universe, Dr. Joshua Frieman of the University of Chicago has released a transcript of a series of lectures he gave on the subject in Rio de Janeiro, Brazil in 2007. He does get mathematical, but if you read through the math, you should come away with a better understanding of the issues that the existence of dark energy presents. Enjoy this 36 page transcript-like lecture series online now here.

Talk about cosmology and there is no escaping the mysteries of dark energy. In an excellent review article, available online at http://xxx.lanl.gov/PS_cache/arxiv/pdf/0901/0901.2724v1.pdf Dr. Ruth Daly takes the readers from the discovery of dark energy in the late 1990s, to the most recent studies of 2008.

The nature of dark energy remains an issue for the new year. The data available to astronomers are still not sufficient to distinguish between the simplest cosmological constant models and the more complex models. Read more about the latest about dark energy in this paper to be published in the International Journal of Modern Physics online now at http://xxx.lanl.gov/PS_cache/arxiv/pdf/0812/0812.4778v1.pdf

In a pre-print accepted for publication and available today online at http://xxx.lanl.gov/PS_cache/arxiv/pdf/0812/0812.4493v1.pdf two methods are analyzed which may provide scientists with an approach for determining the nature of dark energy. One method requires scientists to analyze the density of gas in large clusters of galaxies that emit radiation in the X-ray portion of the spectrum. Another involves analysis of the central density parameter of galaxies, that is, a measure of the mass density of the central region of galaxies which when compared to the measured rotation curve of the galaxy in the central region provides clues to the existence of cold dark matter halos in the vicinity. Previous studies such as this one in Astronomy and Astrophysics available at http://www.aanda.org/index.php?option=article&access=standard&Itemid=129&url=/articles/aa/abs/2006/24/aa4196-05/aa4196-05.html did not support the existence of cold dark matter halos. And, in a yet to be reviewed paper, one Dutch astronomer ponders the possibility of the contribution of “slow-moving” neutrinos to dark matter. See his paper online at http://xxx.lanl.gov/PS_cache/arxiv/pdf/0812/0812.4552v1.pdf

If you think cosmologists are settled about the best model of the universe, you are mistaken. Just today, there appeared a paper online at http://xxx.lanl.gov/PS_cache/arxiv/pdf/081/0812.3912v1.pdf which seeks to provide an alternative to the standard dark energy model while still explaining the supernovae Type Ia results which lead us to believe in the accelerating expansion of the universe. In another paper available online at http://xxx.lanl.gov/PS_cache/arxiv/pdf/0809/0809.3761v2.pdf and accepted for publication in Physical Review Letters, Canadian astronomers provide yet another alternative view of cosmology, without the need for the standard view of dark energy. And yet another paper on dark energy modeling was released today, and is available online at http://xxx.lanl.gov/PS_cache/arxiv/pdf/081/0812.3901v1.pdf within which the interactions of dark energy and cold dark matter are examined.

In a press release yesterday (16 Dec 2008), available online at http://www.nasa.gov/home/hqnews/2008/dec/HQ_08329_DARK_ENERGY.txt NASA announced the latest results from a study completed with the data from the Chandra X-ray observatory. These results lead to a more prosaic understanding of the so-called dark energy. The dark energy is responsible for the apparent acceleration of the expansion of the universe, first detected in the 1990s with supernovae type Ia measurements. This phenomenon we call dark energy, may in fact merely be a manifestation of Albert Einstein’s infamous cosmological constant. The cosmological constant was actually devised by Einstein in order to explain how the universe could be in a static state. You see, Einstein’s original equations called for an expanding universe, but at that time, it was not known that the universe was expanding, so Einstein developed the cosmological constant to keep the universe his equations called for, to be static. He later referred to this as his biggest blunder. However, it may be necessary afterall, in order to explain the accelerating expansion of the universe. Read more details about the study done with the Chandra X-ray telescope data online at http://lanl.arxiv.org/PS_cache/arxiv/pdf/0812/0812.2720v1.pdf And look for more about this in the January 2009 podcast of ASTROCAST.TV

The accelerating expansion of the universe and the existence of dark energy was necessary to explain the first results of a survey of Type Ia supernovae. In a continuing report about high redshift (most distant) supernovae, scientists of the ESSENCE team provide the latest information from their data after four years of operation. If you were curious about the acronym, ESSENCE stands for “Equation of State: SupErNovae trace Cosmic Expansion.” To learn more about this effort to better understand dark energy and the accelerating expansion of the universe, see the team’s latest paper at http://xxx.lanl.gov/PS_cache/arxiv/pdf/0811/0811.4424v1.pdf