* Astronomy

Members Login
Username 
 
Password 
    Remember Me  
Home -> Astronomy News -> Cosmology News -> Dark Energy
Post Info
TOPIC: Dark Energy
Blobrana


L

Posts: 131433
Date:
RE: Dark Energy Test
Permalink  
 

Below a certain frequency threshold, the quantum fluctuations of empty space may contribute to dark energy much the way some materials become superconductors below a critical temperature.

Dark energy is so befuddling that it's causing some physicists to do their science backwards.

"Usually you propose your theory and then work out an experiment to test it" - Christian Beck of Queen Mary, University of London.

A few years ago, however, he and his colleague Michael Mackey of McGill University in Montreal, Canada, proposed a table-top experiment to detect the elusive form of energy, without quite knowing why it might work. Now the pair have come up with the theory behind the experiment.

"It is certainly an upside-down way of doing things" - Christian Beck .
Read more

__________________
Blobrana


L

Posts: 131433
Date:
The stryngbohtyk model
Permalink  
 

Title: The Stryngbohtyk Model of the Universe: a Solution to the Problem of the Cosmological Constant
Authors: Jordi Miralda-Escude

Astronomical observations have shown that the expansion of the universe is at present accelerating, in a way consistent with the presence of a positive cosmological constant. This is a major puzzle, because we do not understand: why the cosmological constant is so small; why, being so small, it is not exactly zero; and why it has precisely the value it must have to make the expansion start accelerating just at the epoch when we are observing the universe. We present a new model of cosmology, which we call the stryngbohtyk model, that solves all these problems and predicts exactly the value that the cosmological constant must have. The predicted value agrees with the observed one within the measurement error. We show that in the stryngbohtyk model, the fact the cosmological constant starts being important at the present epoch is not a coincidence at all, but a necessity implied by our origin in a planet orbiting a star that formed when the age of the universe was of the same order as the lifetime of the star.

Read more (PDF)

__________________
Blobrana


L

Posts: 131433
Date:
RE: Dark Energy
Permalink  
 

The Max-Planck-Institute for extraterrestrial physics is developing and supporting the eRosita (extended Roentgen Survey with an Imaging Telescope Array) Roentgen telescope project with a 21 million euro grant.
One can't see or feel dark energy - nevertheless it is strong enough that is driving apart the universe.
The Roentgen telescope will be ready to search for this mysterious force in 2011.

Source

__________________
Blobrana


L

Posts: 131433
Date:
Dark energy an illusion
Permalink  
 

The quickening pace of our universe's expansion may not be driven by a mysterious force called dark energy after all, but paradoxically, by the collapse of matter in small regions of space.
Astronomers were astonished to discover in 1998 that the expansion of the universe is happening at an ever-increasing rate. The mysterious repulsive force responsible for this was dubbed dark energy, though scientists still do not know what it is.
Now, physicist Syksy Rasanen of CERN in Geneva, Switzerland, says we might not need dark energy after all. As counter-intuitive as it sounds, the increasing rate of expansion might be due to the collapse of small regions of the universe under gravity.

Read more

__________________
Blobrana


L

Posts: 131433
Date:
RE: Dark Energy
Permalink  
 

Title: Dark energy is the cosmological quantum vacuum energy of light particles. The axion and the lightest neutrino
Authors: H. J. de Vega, N. G. Sanchez
(revised v3)

We uncover the general mechanism producing the dark energy(DE).This is only based on well known quantum physics and cosmology. We show that the observed DE originates from the cosmological quantum vacuum of light particles which provides a continuous energy distribution able to reproduce the data. Bosons give positive contributions to the DE while fermions yield negative contributions. As usual in field theory, ultraviolet divergences are subtracted from the physical quantities. The subtractions respect the symmetries of the theory and we normalize the physical quantities to be zero for the Minkowski vacuum. The resulting finite contributions to the energy density and the pressure from the quantum vacuum grow as log a(t) where a(t) is the scale factor, while the particle contributions dilute as 1/a^3(t), as it must be for massive particles. The DE equation of state P=w(z)H turns to be w(z)<-1 with w(z) asymptotically reaching the value -1 from below. A scalar particle can produce the observed DE through its quantum cosmological vacuum provided:(i)its mass is of the order of 10^{-3}eV=1 meV,(ii) it is very weakly coupled and (iii) it is stable on the time scale of the age of the universe. The axion vacuum thus appears as a natural candidate. The neutrino vacuum (especially the lightest mass eigenstate) can give negative contributions to the DE. We find that w(z=0) is slightly below -1 by an amount ranging from -1.5 10^{-3}to -8 10^{-3} while the axion mass results between 4 and 5 meV. We find that the universe will expand in the future faster than the de Sitter universe, as an exponential in the square of the cosmic time. DE arises from the quantum vacua of light particles in FRW cosmological space time in an analogous way to the Casimir effect in Minkowski spacetime with non trivial boundaries.

Read more (31kb, PDF)

__________________
Blobrana


L

Posts: 131433
Date:
Vacuum energy
Permalink  
 

The fate of the cosmos could lie in your bathtub. Or perhaps in your kitchen sink. At least that's the view of Joseph Samuel and Supurna Sinha, physicists at the Raman Research Institute in Bangalore, India. They believe one of the most puzzling aspects of the universe could be explained by something as down-to-earth as soap bubbles.
It's all to do with the cosmological constant, a measure of the energy inherent in empty space. This "vacuum energy" causes space-time to push outwards on itself, a phenomenon that astronomers believe explains why the universe is expanding at ever faster rates. Its value determines whether the universe will accelerate gently forever or eventually rip itself to pieces.
The trouble is, none of our best theories can explain the value of the cosmological constant: it is small, ridiculously small, but not zero.

Source

__________________
Blobrana


L

Posts: 131433
Date:
RE: Dark Energy
Permalink  
 

Title: Interacting Dark Energy: Decay into Fermions
Authors: A. de la Macorra

A dark energy component is responsible for the present stage of acceleration of our universe. If no fine tuning is assumed on the dark energy potential then it will end up dominating the universe at late times and the universe will not stop this stage of acceleration. On the other hand, the equation of state of dark energy seems to be smaller than -1 as suggested by the cosmological data. We take this as an indication that dark energy does indeed interact with another fluid (we consider fermion fields) and we determine the interaction through the cosmological data and extrapolate it into the future. We study the conditions under which a dark energy can dilute faster or decay into the fermion fields. We show that it is possible to live now in an accelerating epoch dominated by the dark energy and without introducing any fine tuning parameters the dark energy can either dilute faster or decaying into fermions in the future. The acceleration of the universe will then cease.

Read more (16kb, PDF)

__________________
Blobrana


L

Posts: 131433
Date:
The WiggleZ project
Permalink  
 

Title: The WiggleZ project: AAOmega and Dark Energy
Authors: Karl Glazebrook, Chris Blake, Warrick Couch, Duncan Forbes, Michael Drinkwater, Russell Jurek, Kevin Pimbblet, Barry Madore, Chris Martin, Todd Small, Karl Forster, Matthew Colless, Rob Sharp, Scott Croom, David Woods, Michael Pracy, David Gilbank, Howard Yee, Mike Gladders

We describe the `WiggleZ' spectroscopic survey of 400,000 star-forming galaxies selected from a combination of GALEX ultra-violet and SDSS + RCS2 optical imaging. The fundamental goal is a detection of the baryonic acoustic oscillations in galaxy clustering at high-redshift (0.5 < z < 1) and a precise measurement of the equation of state of dark energy from this purely geometric and robust method. The survey has already started on the 3.9m Anglo-Australian Telescope using the AAOmega spectrograph, and planned to complete during 2009.

Read more (218kb, PDF)

Read more

__________________
Blobrana


L

Posts: 131433
Date:
RE: Dark Energy
Permalink  
 

Title: Massive neutrinos and dark energy
Authors: Paolo Serra, Rachel Bean, Axel De La Macorra, Alessandro Melchiorri

We consider the impact of the Heidelberg-Moscow claim for a detection of neutrino mass on the determination of the dark energy equation of state. By combining the Heidelberg-Moscow result with the WMAP 3-years data and other cosmological datasets we constrain the equation of state to -1.67< w <-1.05 at 95% c.l., While future data are certainly needed for a confirmation of the controversial Heildelberg-Moscow claim, our result shows that future laboratory searches for neutrino masses may play a crucial role in the determination of the dark energy properties.

Read more (216kb, PDF)

__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

Title: Dark Energy, A Cosmological Constant, and Type Ia Supernovae
Authors: Lawrence M. Krauss, Katherine Jones-Smith (CERCA, Case Western Reserve University), Dragan Huterer (KICP, University of Chicago)

We focus on uncertainties in supernova measurements, in particular of individual magnitudes and redshifts, to review to what extent supernovae measurements of the expansion history of the universe are likely to allow us to constrain a possibly redshift-dependent equation of state of dark energy, w(z). focus in particular on the central question of how well one might rule out the possibility of a cosmological constant w=-1. We argue that it is unlikely that we will be able to significantly reduce the uncertainty in the determination of $w$ beyond its present bounds, without significant improvements in our ability to measure the cosmic distance scale as a function of redshift. Thus, unless the dark energy significantly deviates from w(z)=-1 at some redshift, very stringent control of the statistical and systematic errors will be necessary to have a realistic hope of empirically distinguishing exotic dark energy from a cosmological constant.

Read more (58kb, PDF)

__________________
«First  <  1 … 14 15 16 17 18 … 20  >  Last»  | Page of 20  sorted by
Quick Reply

Please log in to post quick replies.
Home -> Astronomy News -> Cosmology News -> Dark Energy


Create your own FREE Forum
Report Abuse 		Powered by ActiveBoard