Q Discovery of dark energy nabs Nobel Prize for three astronomers Phil Plait Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies! http://www.slate.com/blogs/bad_astr...y_nabs_nobel_prize_for_three_astronomers.html I am very pleased to write that the Nobel Prize for physics this year has been awarded to three astronomers for their discovery of dark energy -- a still-mysterious phenomenon that is causing the expansion of the Universe to accelerate. Saul Perlmutter, Brian Schmidt, and Adam Riess are sharing the award. Back in 1998, Saul and Brian headed up two rival teams trying to observe very distant exploding stars, hoping they would yield better numbers for how fast the Universe expanded. Adam was on Brian's team, and led the work on finding a way to try to understand the behavior of the supernovae. To everyone's surprise, the data indicated the Universe was not just expanding, but expanding faster every day -- it was accelerating. Something must be pushing on the very fabric of space itself, causing it to expand ever-faster. We don't now what it is, exactly, but we call it dark energy, and over the past 12 years, more and more observations have piled up showing that this stuff really is out there. If you want background info on all this, see the Related Posts section below; there are plenty of links to articles I've written on this topic. The folks at Hubble also created a video describing dark energy and what it means for the Universe. http://hubblesite.org/hubble_discoveries/dark_energy/ ... Related posts: - The Universe is expanding at 73.8 +/- 2.4 km/sec/megaparsec! So there. - News: dark energy stunts your growth - The Universe is expanding at 74.2 km/sec/Mpc - Hitting the gas - The Universal expansion revisited - What astronomers do - AAS Post #6: The cosmological not-so-constant UQ
Apparently "Dark" here means accepted hypothesis however with limited understanding so far! Q http://docuwiki.net/index.php?title=Death_of_the_Universe In the farthest reaches of space, a volatile battle is taking place between two forces so great, they may eventually destroy the very universe itself. Known as Dark Matter and Dark Energy, these opposing forces have the capacity to rip apart the universe atom-by-atom. While scientists have previously theorised about a “Big Crunch” where the universe retracts back to its original size, the discovery of Dark Matter and Dark Energy has placed that hypothesis on the backburner. Some astronomers now believe that if Dark Matter offsets Dark Energy then as the universe slowly expands, stars will gradually fade, running out of fuel and leading to a dark, cold and lifeless universe. Others hypothesise a much more violent end where Dark Energy continues to expand the universe at a greater and greater speed. Stronger than gravity, Dark Energy would pull apart everything down to the fundamental particles – the universe’s very fibres. While the universe’s end may be 50 billion years away, great leaps in science will continue to alter how we believe the universe was formed – and how it will end. UQ
Q In physical cosmology and astronomy, dark energy is an unknown form of energy which is hypothesized to permeate all of space, tending to accelerate the expansion of the universe.[1] Dark energy is the most accepted hypothesis to explain the observations since the 1990s indicating that the universe is expanding at an accelerating rate. Assuming that the standard model of cosmology is correct, the best current measurements indicate that dark energy contributes 68.3% of the total energy in the present-day observable universe. The mass–energy of dark matter and ordinary (baryonic) matter contribute 26.8% and 4.9%, respectively, and other components such as neutrinos and photons contribute a very small amount. ... ... Nature of dark energy Many things about the nature of dark energy remain matters of speculation.[12] The evidence for dark energy is indirect but comes from three independent sources: * Distance measurements and their relation to redshift, which suggest the universe has expanded more in the last half of its life.[13] * The theoretical need for a type of additional energy that is not matter or dark matter to form the observationally flat universe (absence of any detectable global curvature). * It can be inferred from measures of large scale wave-patterns of mass density in the universe. Dark energy is thought 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 quite rarefied — roughly 10−27 kg/m3 — it is unlikely to be detectable in laboratory experiments. Dark energy can have such a profound effect on the universe, making up 68% of universal density, only because it uniformly fills otherwise empty space. The two leading models are a cosmological constant and quintessence. Both models include the common characteristic that dark energy must have negative pressure. UQ Q http://www.bbc.com/earth/story/20150602-how-will-the-universe-end Dark energy pulls the universe apart They tried to perform a cosmic census, adding up how much stuff there is in our universe. It turned out that we're strangely close to the critical threshold, leaving our fate uncertain. That all changed at the end of the 20th century. In 1998, two competing teams of astrophysicists made an astonishing announcement: the expansion of the universe is speeding up. Normal matter and energy can't make the universe behave this way. This was the first evidence of a fundamentally new kind of energy, dubbed "dark energy", which didn't behave like anything else in the cosmos. Dark energy pulls the universe apart. We still don't understand what it is, but roughly 70% of the energy in the universe is dark energy, and that number is growing every day. The existence of dark energy means that the amount of stuff in the universe doesn't get to determine its ultimate fate. Instead, dark energy controls the cosmos, accelerating the expansion of the universe for all time. This makes the Big Crunch much less likely. UQ
Q https://en.wikipedia.org/wiki/Dark_matter Dark matter is a hypothetical kind of matter that cannot be seen with telescopes but accounts for most of the matter in the universe. The existence and properties of dark matter are inferred from its gravitational effects on visible matter, on radiation, and on the large-scale structure of the universe. Dark matter has not been detected directly, making it one of the greatest mysteries in modern astrophysics. Dark matter neither emits nor absorbs light or any other electromagnetic radiation at any significant level. According to the Planck mission team, and based on the standard model of cosmology, the total mass–energy of the known universe contains 4.9% ordinary (baryonic) matter, 26.8% dark matter and 68.3% dark energy.[2][3] Thus, dark matter is estimated to constitute 84.5%[note 1] of the total matter in the universe, while dark energy plus dark matter constitute 95.1% of the total mass–energy content of the universe. Astrophysicists hypothesized the existence of dark matter to account for discrepancies between the mass of large astronomical objects determined from their gravitational effects, and their mass as calculated from the observable matter (stars, gas, and dust) that they can be seen to contain. Their gravitational effects suggest that their masses are much greater than the observable matter survey suggests. ... ... According to observations of structures larger than star systems, as well as Big Bang cosmology interpreted under the Friedmann equations and the Friedmann–Lemaître–Robertson–Walker metric, dark matter accounts for 26.8% of the mass-energy content of the observable universe. In comparison, ordinary (baryonic) matter accounts for only 4.9% of the mass-energy content of the observable universe, with the remainder being attributable to dark energy.[18] From these figures, matter accounts for 31.7% of the mass-energy content of the universe, and 84.5% of the matter is dark matter. Dark matter plays a central role in state-of-the-art modeling of cosmic structure formation and galaxy formation and evolution and has measurable effects on the anisotropies observed in the cosmic microwave background (CMB). All these lines of evidence suggest that galaxies, clusters of galaxies, and the universe as a whole contain far more matter than that which is easily visible with electromagnetic radiation.[16] Though the theory of dark matter remains the most widely accepted theory to explain the anomalies in observed galactic rotation, some alternative theoretical approaches have been developed which broadly fall into the categories of modified gravitational laws and quantum gravitational laws. ... ... Dark matter is crucial to the Big Bang model of cosmology as a component which corresponds directly to measurements of the parameters associated with Friedmann cosmology solutions to general relativity. In particular, measurements of the cosmic microwave background anisotropies correspond to a cosmology where much of the matter interacts with photons more weakly than the known forces that couple light interactions to baryonic matter. Likewise, a significant amount of non-baryonic, cold matter is necessary to explain the large-scale structure of the universe. Observations suggest that structure formation in the universe proceeds hierarchically, with the smallest structures collapsing first and followed by galaxies and then clusters of galaxies. As the structures collapse in the evolving universe, they begin to "light up" as the baryonic matter heats up through gravitational contraction and approaches hydrostatic pressure balance. Originally, baryonic matter had too high a temperature, and pressure left over from the Big Bang to allow collapse and form smaller structures, such as stars, via the Jeans instability. Dark matter acts as a compactor allowing the creation of structure where there would not have been any.This model not only corresponds with statistical surveying of the visible structure in the universe but also corresponds precisely to the dark matter predictions of the cosmic microwave background. This bottom up model of structure formation requires something like cold dark matter to succeed. Large computer simulations of billions of dark matter particles have been used[77] to confirm that the cold dark matter model of structure formation is consistent with the structures observed in the universe through galaxy surveys, such as the Sloan Digital Sky Survey and 2dF Galaxy Redshift Survey, as well as observations of the Lyman-alpha forest. These studies have been crucial in constructing the Lambda-CDM model which measures the cosmological parameters, including the fraction of the universe made up of baryons and dark matter. The recent discovery of the structure of Laniakea, a 500 million light year structure is currently the limit to structural formation in the universe. However, Laniakea is not gravitationally bound and is projected to be torn apart by dark energy.[78] There are, however, several points of tension between observation and simulations of structure formation driven by dark matter. There is evidence that there exist 10 to 100 times fewer small galaxies than permitted by what the dark matter theory of galaxy formation predicts.[79][80] This is known as the dwarf galaxy problem. In addition, the simulations predict dark matter distributions with a very dense cusp near the centers of galaxies, but the observed halos are smoother than predicted. UQ