Subscribe:
RSS feed
"Everything should be as simple as it is, but not simpler", Albert Einstein
Browsing All Posts filed under »DARK ENERGY«
Can dark energy be gravitational waves?
Peter L. Biermann, Benjamin C. Harms The idea that dark energy is gravitational waves may explain its strength and its time-evolution. A possible concept is that dark energy is the ensemble of coherent bursts (solitons) of gravitational waves originally produced when the first generation of super-massive black holes was formed. These solitons get their initial […]
First result from the AMS experiment
April 3, 2013
The Alpha Magnetic Spectrometer (AMS) Collaboration announces the publication of its first physics result in Physical Review Letters. The AMS Experiment is the most powerful and sensitive particle physics spectrometer ever deployed in space. As seen in Figure 1, AMS is located on the exterior of the International Space Station (ISS) and since its installation […]
Dark energy from entanglement entropy
March 9, 2013
Salvatore Capozziello, Orlando Luongo We show that quantum decoherence, in the context of observational cosmology, can be connected to the cosmic dark energy. The decoherence signature could be characterized by the existence of quantum entanglement between cosmological eras. As a consequence, the Von Neumann entropy related to the entanglement process, can be compared to the […]
Ground-Based Instruments Could Detect Cosmic Wall Structures
January 14, 2013
Invisible sheetlike structures, which might pervade space and contribute to dark matter or dark energy, could be revealed as they pass by Earth-based detectors. One of the potential explanations for the Universe’s mysterious dark matter and dark energy is a cosmic latticework of energetic “domain walls.” In Physical Review Letters, a team proposes the first […]
Theoretical Models of Dark Energy
December 20, 2012
Jaewon Yoo, Yuki Watanabe Mounting observational data confirm that about 73% of the energy density consists of dark energy which is responsible for the current accelerated expansion of the Universe. We present observational evidences and dark energy projects. We then review various theoretical ideas that have been proposed to explain the origin of dark energy; […]
How Einstein Discovered Dark Energy
December 1, 2012
Alex Harvey In 1917 Einstein published his Cosmological Considerations Concerning the General Theory of Relativity. In it was the first use of the cosmological constant. Shortly thereafter Schröodinger presented a note providing a solution to these same equations with the cosmological constant term transposed to the right hand side thus making it part of the […]
Dark Energy and Dark Matter as Inertial Effects
October 16, 2012
Serkan Zorba A rigidly rotating model of the universe is postulated. It is shown that dark energy and dark matter are cosmic inertial effects resulting from such a cosmic rotation, corresponding to centrifugal and a combination of centrifugal and the Coriolis forces, respectively. The physics and the cosmological and galactic parameters obtained from the model […]
Gravitational Field Equations and Theory of Dark Energy and Dark Matter
September 7, 2012
Mathematicians offer unified theory of dark matter, dark energy, altering Einstein field equations A pair of mathematicians—one from Indiana University and the other from Sichuan University in China—have proposed a unified theory of dark matter and dark energy that alters Einstein’s equations describing the fundamentals of gravity. Shouhong Wang, a professor in the IU College […]
Euclid telescope to probe dark universe
June 20, 2012
Europe has given the final go-ahead to a space mission to investigate the “dark universe”. The Euclid telescope will look deep into the cosmos for clues to the nature of dark matter and dark energy. These phenomena dominate the Universe, and yet scientists concede they know virtually nothing about them. European Space Agency (Esa) member states made […]
Is Dark Matter a Glimpse of a Deeper Level of Reality?
June 11, 2012
(……) String theorists and other would-be unifiers of physics face a basic problem. The theories they seek to unify, quantum field theory and Einstein’s general theory of relativity, are well-grounded and well-tested, yet mutually incompatible. Reconciling them will demand that some deeply held intuition must give way. One such intuition is that the world exists […]
Physicists hunt for dark forces
April 4, 2012
Cheap colliders probe debris for hint of ‘heavy’ photon. Eric Hand n tunnels beneath the Thomas Jefferson National Accelerator Facility in Newport News, Virginia, an accelerator whips a beam of electrons around a racetrack. Their energies are modest, but the beam is tightly packed with them — for it takes a very bright beam to […]
The Cosmological Constant Problem, Dark Energy, and the Landscape of String Theory
March 5, 2012
Raphael Bousso In this colloquium-level account, I describe the cosmological constant problem: why is the energy of empty space at least 60 orders of magnitude smaller than several known contributions to it from the Standard Model of particle physics? I explain why the “dark energy” responsible for the accelerated expansion of the universe is almost […]
Is Dark Energy Falsifiable?
December 14, 2011
Carl H. Gibson (University of California at San Diego), Rudolph E. Schild (Harvard University) Is the accelerating expansion of the Universe true, inferred through observations of distant supernovae, and is the implied existence of an enormous amount of anti-gravitational dark energy material driving the accelerating expansion of the universe also true? To be physically useful […]
An interpretation of the acceleration of the universe’s expansion
November 5, 2011
Dong-Biao Kang We have observed the acceleration of the expansion of the universe. To explain this phenomenon, we usually introduce the dark energy (DE) which has a negative pressure or we need to modify the Einstein’s equation to produce a term which is equivalent to the dark energy. Are there other possibilities? Combining our previous […]
Universe’s expansion may be understood without dark energy
October 24, 2011
Least-time paths of light by Arto Annila ABSTRACT The variational principle in its original form á la Maupertuis is used to delineate paths of light through varying energy densities and to associate shifts in frequency and changes in momentum. The gravitational bending and Doppler shift are in this way found as mere manifestations of least-time […]
Lectures on Cosmology and Particle Physics
October 20, 2011
by Sean Carroll Lecture One: Introduction to Cosmology http://youtu.be/vUNtO2r_-eo Lecture Two: Dark Matter http://youtu.be/Gq-lGX2PRrc Lecture Three: Dark Energy http://youtu.be/cYVj2RhXxeU Lecture Four: Thermodynamics and the Early Universe http://youtu.be/178mMnGvWs0 Lecture Five: Inflation and Beyond http://youtu.be/M1PeXaMqKto
Attraction-repulsion coupled and energy conserved universe
October 16, 2011
Ti-Pei Li The discovery of an accelerating cosmic expansion rate implies that, in addition to the attractive gravity of matter, there exist in our universe some other form of energy (dark energy or cosmological constant) producing a repulsive force. The natural interpretation of dark energy is the vacuum energy. However, the density of vacuum energy […]
Interacting Dark Energy — constraints and degeneracies
October 15, 2011
Timothy Clemson, Kazuya Koyama, Gong-Bo Zhao, Roy Maartens, Jussi Väliviita In standard cosmologies, dark energy interacts only gravitationally with dark matter. There could be a non-gravitational interaction in the dark sector, leading to changes in the effective DE equation of state, in the redshift dependence of the DM density and in structure formation. We use […]
Why Einstein was wrong about being wrong
October 14, 2011
There really is a mysterious antigravity force. Einstein’s only mistake was in rejecting it. By Michael D. Lemonick If you want to get your mind around the research that won three astronomers the Nobel Prize in physics last week, it helps to think of the universe as a lump of dough — raisin-bread dough, to […]
What do we really know about Dark Energy?
October 9, 2011
Ruth Durrer In this paper I discuss what we truly know about dark energy. I shall argue that up to date our single indication for the existence of dark energy comes from distance measurements and their relation to redshift. Supernovae, CMB anisotropies and observations of baryon acoustic oscillations, they all simply tell us that the […]
Dark Energy FAQ
October 5, 2011
In honor of the Nobel Prize, here are some questions that are frequently asked about dark energy, or should be. What is dark energy? It’s what makes the universe accelerate, if indeed there is a “thing” that does that. (See below.) So I guess I should be asking… what does it mean to say the universe […]
Europe to lead daring Sun mission
October 5, 2011
Europe is to lead the most ambitious space mission ever undertaken to study the behaviour of the Sun. Known as Solar Orbiter, the probe will have to operate a mere 42 million km from our star – closer than any spacecraft to date. The mission proposal was formally adopted by European Space Agency (Esa) member […]
Physics Nobel will attract controversy
October 4, 2011
Assigning credit for a scientific discovery is never easy, especially when two rival, interacting teams of scientists are involved. That is exactly the problem that the Nobel committee must have grappled with before awarding this year’s physics prize to Saul Perlmutter, Adam Riess and Brian Schmidt. Perlmutter led the Supernova Cosmology Project, while Schmidt and Riess were […]
Nobel Prize in Physics 2011
October 4, 2011
(update) The Nobel Prize in Physics 2011 has been awarded to Saul Perlmutter, Brian P Schmidt and Adam G Riess for discovering the accelerating expansion of the universe ………………………………………………………. Three scientists shared the 2011 Nobel Prize for physics for the stunning discovery that the expansion of the universe is speeding up, meaning it may one […]
Dark matter
September 27, 2011
A review of the development of the concept of dark matter. The dark matter story passed through several stages from a minor observational puzzle to a major challenge for theory of elementary particles. Modern data suggest that dark matter is the dominant matter component in the Universe, and that it consists of some unknown non-baryonic […]
Long-wavelength gravitational waves and cosmic acceleration
September 22, 2011
Strong long-scale gravitational waves can explain cosmic acceleration within the context of general relativity without resorting to the assumption of exotic forms of matter such as quintessence. The existence of these gravitational waves in sufficient strength to cause observed acceleration can be compatible with the cosmic microwave background under reasonable physical circumstances. An instance of […]
Virial estimator for dark energy
September 7, 2011
A.D. Chernin et al A new estimator of the local density of dark energy is suggested which comes from the virial theorem for non-relativistic gravitating systems embedded in the uniform dark energy background. 1 Introduction The virial theorem of Newtonian mechanics plays a central part in the studies of gravitationally bound quasi-stationary astronomical many-body systems […]
Interview with Lucio Mayer on world’s first realistic simulation of the formation of Milky Way
August 30, 2011
First glimpse into birth of the Milky Way – For almost 20 years astrophysicists have been trying to recreate the formation of spiral galaxies such as our Milky Way realistically. Now astrophysicists from the University of Zurich present the world’s first realistic simulation of the formation of our home galaxy together with astronomers from the […]
Dark Energy, Dark Matter, Dark Force: Not Afraid Of The Dark
August 19, 2011
Sascha Vongehr The public repulsion against dark matter and dark energy is really annoying. Rob Knop at scientopia compares it to 17th century catholic church mentality; Ethan picks it up and bangs the dark matter explains everything drum although dark matter does not fit very well to galaxy rotation curves – Modified Newtonian Dynamics (MOND) fits much better: (From: Begeman, Broeils, […]
No privilege for earthly observers
July 22, 2011
Confirmation of the Copernican Principle at Gpc Radial Scale and above from the Kinetic Sunyaev-Zel’dovich Effect Power Spectrum Pengjie Zhang and Albert Stebbins Phys. Rev. Lett. 107, 041301 (Published July 21, 2011) According to most cosmologists, there is nothing special about us as observers of the universe. Still, some theories shirk this so-called Copernican principle, […]
The Hubble constant and dark energy
July 18, 2011
The Hubble Constant measured from the anisotropy in the cosmic microwave background (CMB) is shown to be independent of small changes from the standard model of the redshift dependence of dark energy. Modifications of the Friedmann equation to include phantom power (w < –1), textures (w = –2/3) and curvature are considered, and constraints on […]
Dark-energy fingerprints found in ancient radiation
July 15, 2011
Only cat burglars can match the stealth of dark energy, credited with speeding up the universe’s expansion over time, but now its fingerprints have been glimpsed in the universe’s oldest radiation. The strongest evidence for dark energy comes from supernovae, which suggest the universe is expanding faster now than in the past. But the force should also change […]
May 4, 2013
0