Tag archives: dark energy
By Matin Durrani
Unless you’re prepared to modify our understanding of gravity – and most physicists are not – the blunt fact is that we know almost nothing about 95% of the universe. According to our best estimates, ordinary, visible matter accounts for just 5% of everything, with 27% being dark matter and the rest dark energy.
The July issue of Physics World, which is out now in print and digital formats, examines some of the mysteries surrounding “the dark universe”. As I allude to in the video above, the difficulty with dark matter is that, if it’s not ordinary matter that’s too dim to see, how can we possibly find it? As for dark energy, we know even less about it other than it’s what is causing the expansion of the universe to accelerate and hence making certain supernovae dimmer (because they are further away) than we’d expect if the cosmos were growing uniformly in size.
By Calla Cofield at the APS April Meeting in Savannah, Georgia
Scientists looking at data from the Baryon Oscillation Spectroscopic Survey (BOSS), the largest programme in the third Sloan Digital Sky Survey, have measured the expansion rate of the universe 10.8 billion years ago — a time prior to the onset of accelerated expansion caused by dark energy. The measurement is also the most precise measurement of a universal expansion rate ever made, with only 2% uncertainty. The results were announced at a press conference at the APS’s April meeting on Monday, at the same time that the results were posted on the arXiv preprint server.
The rate of universal expansion has changed over the course of the universe’s lifetime. It is believed to have gradually slowed down after the Big Bang, but mysteriously began accelerating again about 7 billion years ago. BOSS and other observatories have previously measured expansion rates going back 6 billion years.
By Michael Banks in Boston
Dust is annoying, particularly when you want to obtain a precise measurement of the expansion of the universe.
Today, Robert Kirshner from Harvard University gave a plenary lecture at the 2013 AAAS meeting in Boston giving participants a tour of the latest in dark-energy research.
Kirshner is a member of the High-Z team that some 15 years ago used observations of supernovae to discover that the expansion of the universe is accelerating.
Indeed, his former students – Brian Schmidt and Adam Riess – shared the 2011 Nobel Prize for Physics together with Saul Perlmutter for this discovery.
Riess, a graduate student at the time, played an important part in figuring out how to account for dust when measuring supernovae distances. This dust surrounding a supernovae is annoying as it absorbs light, which introduces uncertainties in deducing how far away supernovae are.
Reiss managed to account for this well enough to measure the brightness of supernovae to a reasonable precision that could then be used to deduce the accelerating expansion of the universe; but now Kirshner’s team is planning to go a few steps further by doing better measurements.
Artist’s impression of a map of the Quantum Universe (Graphic courtesy of “ILC — form one visual communication”)
By Tushna Commissariat
Here’s a bit of Friday physics fun… I came across this rather interesting image that shows an artist’s impression of a map entitled “The Quantum Universe”. It includes six landmasses all floating in the Big Bang Ocean; including Dark Matter Landmass, Sypersymmetry Reef, Higgs Island and the Land of Ultimate Unification as well as others.
So go ahead and tell us which island you would like to settle down on. Be sure to look carefully at gems like Newton’s Lawn and Mount Einstein before you make your mind up!
To see a larger hi-res image follow this link.