Dark energy Definition and 553 Threads

In Lee Smolin's book, The Trouble with Physics, pages 15 and 16, he states: Can someone explain how this works? Does this mean that modifications to gravity causing tension at large intergalactic scales could account for the accelerating expansion of the universe as well?

http://curious.astro.cornell.edu/question.php?number=760 Yep, it's an exception to the rule that "nothing can escape a black hole".

I was curious about whether or not the Universe was accelerating or decelerating and how we could know one way or another. I read an article I found online http://curious.astro.cornell.edu/question.php?number=63" and it said that, among other things, that the universe is accelerating partly...

Sean Carroll has an excellent account of a new paper by Rachel Bean. I don't always share Carroll's attitudes or appreciate his reporting, but here's a case where I thought his post was top notch. You may have already read his posting and if not I hope you will. Meanwhile let's take a cue from...

I am starting this thread because this is something Sylas and me were discussing off topic on another thread, but I would welcome more clarification on this. If I understand this correctly galaxies are not moving apart because there is a force acting on them which overcomes gravity, and...

Have you seen this paper, Federico Urban and Ariel Zhitnitsky, "The QCD Nature of Dark Energy", http://lanl.arxiv.org/abs/0909.2684", They claim can generate approximately the right amount of dark energy in the universe, just from the effect of the normal Hubble expansion upon the QCD vacuum...

Can someone remind me what the difference between the Cosmological Constant (\Lambda) and Dark Energy (DE)? Doesn't DE (with w = -1) show up in the Einstein's field equations in exactly the same way as \Lambda does? (In case your an expert, I was trying to understand the conclusion of...

This is a question relating to the current observation, and what exactly they mean. According to Lorentz Contraction, it's impossible to tell which way we're headed, because increased velocities should result in shorter distances. We theorize exactly the opposite, at an accelerated rate. Is...

No evidence for dark energy---------- http://arxiv.org/PS_cache/arxiv/pdf/0908/0908.3186v1.pdf We use a variant of principal component analysis to investigate the possible temporal evolution of the dark energy equation of state, w(z). We constrain w(z) in multiple redshift bins, utilizing the...

There was an article in the Proceedings of the National Academy of Sciences where the authors derived a model which explained the accelerated expansion of the Universe without needing the ad hoc assumption of Dark Energy. I haven't really done any cosmology yet so I can't really appreciate the...

Black holes and dark energy. which has more control over the other?

Could someone please explain how to interpret a negative dark energy density -\Omega_{\Lambda}? How is a density allowed to be negative?

It is my understanding that there is evidence from the red shift/distance relationship that while the rate of universal expansion was once decreasing (from the Big Bang until about 6-7 billion years ago -BYA for short), at about 6-7 BYA it began increasing. This, as I understand it, is the main...

I keep reading that the energy scale of inflation is possibly 1024eV, while the energy scale of dark energy is around 10-3eV. What exactly are these scales referring to? Is it the energy required to accelerate the universe at the corresponding rates of acceleration? What...

I'm having trouble finding an article or paper on the observational evidence for dark energy being a cosmological constant. I'm looking at this Living Review by Sean Carroll http://relativity.livingreviews.org/Articles/lrr-2001-1/ and he only describes how supernova data constrain the...

Are there any theories of gravitation and spacetime that don't require the existence of dark matter to explain the peculiar rotation of galaxies and don't require dark energy to explain the expansion of space? I would love some links. These things just seem suspiciously like luminiferous...

Hello: It has been said that something on the order of 75% of the known universe is comprised of dark energy. But, unless one is assigning a negative value to the putative mass that would be associated with that dark energy, then I don't quite see how one can come up with the 75% figure --...

In the late 1920's it was observed that galaxies in virtually all directions were moving apart from us, and/or we from them, at a rate that increases with distance. Implicit within this observation was the fact that there is a mechanism that would have caused this increasing rate of separation...

At this point, I am rather confused about the concept of DE, and even why it is called DE since it does not seem to fit into what the concept of energy is. but my question is where/how does DE fit into the standard model? thanks.

It appears that the Dark Energy concept was born out of a need to explain the two major observational phenomenons (increasing rate of expansion of the Universe and the faster-than-expectated-rotation of the galactic outer-rim). If I'm not mistaken, this also has to do with gravity seemingly...

I've read that Dark Energy was invented to explain why galaxies really far away are moving away from us faster than ones closer to us. Now I'm sure they did this, but did they take into account that if they look at 2 galaxies A and B. Galaxy A is 500 million ly away and B is 5billion ly away...

I assumed Dark energy is no exception to Einstein famous energy equation. What would dark mass look like, I mean besides it having the quality of darkness? What would distinguish dark mass from non-dark mass?

What I keep hearing is that dark energy acts like a sort of 'negative pressure', causing all the objects in the universe to accelerate away from one another, or a 'constant energy density filling space'. Something I have been unable to understand is what the nature of this "negative pressure" or...

No need for "dark energy", gravity will suffice. In 1929 it was observed that, with rare exception, galaxies in all directions are exhibiting degrees of red-shift that increase with distance. This information alone is sufficient to, (a), describe the structure of the universe, (b), state that...

rank amateur here - as i currently understand it, dark energy does not react with anything so we cannot detect it directly. DE is deduced from macro scale observations of the movements of distant galaxies, which arent behaving as they should given the amount of observed mass. (i hope all that...

If there is Dark Energy expansion of space throughout this Universe why is it not noticed, at least to some extent, within our Solar system? Can it only be noticed on a Grand Scale?

Hi, My name is Brandon, I am new here. My physics knowledge mostly comes from surfing the net, so I have a lot of gaps in my understanding. But i do love the stuff, and i try to stay open to it. Anyway, i know about dark energy and the expansion of the universe. and i guess the...

This guy uses lattice to calculate how gravity would behave in a non commutative aproximation. His insight is interesting given that gravitons interact among themselves pretty much like gluons. http://arxiv.org/abs/0901.4005 I am extremely surprised of how well that describes the whole thing

Hello everybody, I am new to this forum and cosmology in general. My knowledge about cosmology and astro-physics is rudimentary :shy: so guys cut me some slack. From the limited information I know , I feel that phenomenon of gravity leaking might be related to the phenomenon of the...

Okay, so being fourteen, I know that I'm way out of my league on this forum. I do my best to understand anything to do with physics and to at least get a vague idea of theories and ideas, both old and new. Please forgive me for my ignorance. Aside from one topic a while back, I havn't done...

Hey! I made a similar question in another post and it was really useful, but I'd like to learn more about this relation, and why the propieties of SNe Ia make them so special, so we can call them standard candels and how did they lead us to the discovery of Dark Energy. Thank you!:smile:

The brain and "dark energy"? Hello, hopefully I have this question in the right category... I was just reading an article about the brain and "dark energy". It was talking about how there's apparently a connection to the human brain and this so-called "dark energy" that makes up about 70% of...

Hi, I have another doubt :biggrin: In addition to the Supernovae Ia, which more brought us to think the expansion was accelerating? And is there any difference between dark energy and quintessence? Because I've heard that dark energy is like vacuum energy (cosmological constant) and...

The Chandra X-Ray Observatory has revealed that galaxies aren't accumulating lots more matter over time: http://www.csmonitor.com/2008/1218/p01s07-usgn.html http://blogs.nature.com/news/thegreatbeyond/2008/12/new_clues_for_dark_energy_1.html...

Hi I have to do a project, and I've chosen dark energy as the principal item. But first I talk of the evolution of the Univers and others. I just wanted to comment you the structure of the project and see if you thank it's good or you'd do it of another way. 1. Introduction 2. Main methods...

Well, the title says the most, but the question is: If Virtual particles exist... Could it be dark energy?, if it really can, would it be the same idea of a Cosmological Constant??Thanks!

arXiv:0811.3606 (cross-list from astro-ph) [ps, pdf, other] Title: Large-scale cosmic flows and moving dark energy Authors: Jose Beltran Jimenez, Antonio L. Maroto Comments: 5 pages, 2 figures. Corrected references Subjects: Astrophysics (astro-ph); General Relativity and Quantum...

why is the temperature distribution of hot gases inside galaxies evidence for dark matter and why is Type 1a Supernovae evidence for dark energy

Hello, I'm pretty uneducated on the topic of dark matter and dark energy, but I know a little. I was just wondering why dark matter and dark energy are the more "expected to be true" theories then many others currently. I'm not suggesting that the following theories are right or wrong, I'm...

This applies to the small extra dimensions. The rolled-up compact kind that we wouldn't see if they were there. Paul Steinhardt has just posted a paper proving no-go theorems that exhibit an impressive degree of incompatibility between compact extra dimensions on the one hand versus the...

The purpose of this thread is not so much to discuss immature details but to see what the general opinon is about the suggestions that "dark energy" might be understood as a kind of information energy. As far as I know, I have not myself seen any fully satisfactory papers on this, but there...

How much have the universe expanded the past 1 -2 - 3 - 4- 5 – 6 - 7-8 – 9 – 10 - 11- 12 to 13,7 billion year ?

Is dark energy constant to emtpy space?? i've just been reading about dark energy on a site, and it seems it's quite a riddle at present. it stated that the dark energy of space is constant and that the universe is speeding up as the more space produced increases the amount of dark energy...

According to an article on the CERN website 'dark energy' is detected by its 'gravitational effect': Most of the Universe is made up of invisible substances known as 'dark matter' (26%) and 'dark energy' (70%). These do not emit electromagnetic radiation, and we detect them only through their...

'XMM-Newton’s massive discovery' 25 August 2008 'ESA’s orbiting X-ray observatory XMM-Newton has discovered the most massive cluster of galaxies seen in the distant Universe until now. The galaxy cluster is so big that there can only be a handful of them at that distance, making this a rare...

http://space.newscientist.com/channel/astronomy/cosmology/dn14546-biggest-3d-galaxy-map-to-probe-dark-energys-history.html In this cosmic cacophony, one particular note was louder than the rest, and it survives to this day as a characteristic wavelength in the clustering of galaxies...

Direct Evidence of “Dark Energy” (?) Hawaii Scientists Find Direct Evidence of “Dark Energy” in Supervoids and Superclusters superclusters & supervoids A team of astronomers at the University of Hawaii Institute for Astronomy (IfA) led by Dr. István Szapudi has found direct evidence for...

Is it possible to relate the hypothesized dark energy of the universe with the CMB wavelength?

arXiv:0807.1635 [ps, pdf, other] Title: Dark energy: myths and reality Authors: V.N. Lukash (Astro Space Centre of P.N. Lebedev Physical Institute, Moscow, Russia), V.A. Rubakov (Institute for Nuclear Research, Moscow, Russia) Comments: 17 pages, 2 figures Journal-ref...

Paper referred to http://www.calphysics.org/zpe.html In one paragraph they talk about (wave fragments), How could such an enormous energy not be wildly evident? There is one major difference between zero-point electromagnetic radiation and ordinary electromagnetic radiation. Turning again to...