Dark energy Definition and 559 Threads

In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. The first observational evidence for its existence came from measurements of supernovae, which showed that the universe does not expand at a constant rate; rather, the expansion of the universe is accelerating. Understanding the evolution of the universe requires knowledge of its starting conditions and its composition. Prior to these observations, it was thought that all forms of matter and energy in the universe would only cause the expansion to slow down over time. Measurements of the cosmic microwave background suggest the universe began in a hot Big Bang, from which general relativity explains its evolution and the subsequent large-scale motion. Without introducing a new form of energy, there was no way to explain how an accelerating universe could be measured. Since the 1990s, dark energy has been the most accepted premise to account for the accelerated expansion. As of 2021, there are active areas of cosmology research aimed at understanding the fundamental nature of dark energy.Assuming that the lambda-CDM model of cosmology is correct, the best current measurements indicate that dark energy contributes 68% of the total energy in the present-day observable universe. The mass–energy of dark matter and ordinary (baryonic) matter contributes 26% and 5%, respectively, and other components such as neutrinos and photons contribute a very small amount. The density of dark energy is very low (~ 7 × 10−30 g/cm3), much less than the density of ordinary matter or dark matter within galaxies. However, it dominates the mass–energy of the universe because it is uniform across space.Two proposed forms of dark energy are the cosmological constant, representing a constant energy density filling space homogeneously, and scalar fields such as quintessence or moduli, dynamic quantities having energy densities that can vary in time and space. Contributions from scalar fields that are constant in space are usually also included in the cosmological constant. The cosmological constant can be formulated to be equivalent to the zero-point radiation of space i.e. the vacuum energy. Scalar fields that change in space can be difficult to distinguish from a cosmological constant because the change may be extremely slow.
Due to the toy model nature of concordance cosmology, some experts believe that a more accurate general relativistic treatment of the structures that exist on all scales in the real universe may do away with the need to invoke dark energy. Inhomogeneous cosmologies, which attempt to account for the back-reaction of structure formation on the metric, generally do not acknowledge any dark energy contribution to the energy density of the Universe.

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  1. C

    Dark energy acceleration of space effect on red shift

    I have not seen this discussed so this a question in the form of a statement for clarity. If light left a star 10 billion years ago and space has expanded for 10 billion years before the light is observed the light frequency would be stretched out or red shifted therefore some of the red...
  2. P

    Dark matter and dark energy as a relativistic mass?

    According to the theory of relativity, the universe should expand from the center (place of Big Bang) with a maximum possible radial speed close to the speed of light c. So, the galaxies and intergalactic matter moves with a radial speed close to the speed of light too. For instance, this allows...
  3. L

    Exploring My Misunderstanding of Dark Energy

    I'm no cosmologist and my understanding of dark energy is probably below that of a layperson's. But I'm misunderstanding not only what dark energy is (which apparently nobody understands), but even the concept of it. The main thing I don't get is that they say it makes up ~70% of the...
  4. wolram

    Dark Energy Horizon: Light's Eternal Boundary?

    Where is the boundary that light will never reach us, and will light seem to stand still at this boundary if so will there be a cosmic ring of light from some observer?
  5. N

    Naive Understanding of Dark Matter and Dark Energy

    Hello all, I am still an undergraduate, but I would like to ask a really naive question. From a cosmological point of view, does the necessity for the introduction of Dark Matter and Dark Energy in order to satisfy our current models of prediction mean that our models are fundamentally...
  6. J

    Cassimir's Dark Energy Plate Experiment

    I was watching Nova: Fabric of the Cosmos, and there was a part where they were discussing Hendrick Cassimir's dark energy plate experiment. If the plates move, then that is work being performed, right? Isn't it conceivable that this energy is capable of being harnessed regardless of how much...
  7. P

    Universe is speeding up? Are we traveling with it? Dark Energy.

    Hi, new and pondering with much ignorance. Hence the question marks. Had to register! Are we traveling, is our planet, solar system moving along with the universe expansion? This question, statement, is prefaced on the theory that the universe is speeding up rather than slowing down. I...
  8. T

    Does Dark Energy break the Conservation of Energy?

    As the expansion of space accelerates, space is created and this seems to break the conservation of energy law. I've googled this but have not found a really good explanation of this. Imagine for a moment we're so far into the future that there are vast vast voids between what remains of...
  9. S

    Could Dark Energy Originate from Gravity Waves?

    A new paper appeared on the arxiv today suggesting this possibility: http://uk.arxiv.org/abs/1305.0498 I would not have paid too much attention apart from the fact that when this was suggested a while back it was said it might explain some of the WMAp anomalies...
  10. M

    Is Dark Energy Truly Real? What Do Scientists Know and Who Rejects It?

    Where did scientists reach so far about this matter? Any who had rejected it?
  11. C

    Dark Energy an effect of inhomogeneity?

    This new paper Local Large-Scale Structure and the Assumption of Homogeneity claims that a combined analysis of several surveys indicates that there is a substantial local under-density in the universe on the order of 800 MPC in size. Previous work done by other authors suggests that an...
  12. wolram

    Searching for Dark Energy, Dark Matter & Gravitational Radiation

    How is the search for dark matter, dark energy and gravitational radiation going, as far as i can make out there has been no direct detection and they remain conjectures
  13. A

    Is dark energy or dark matter created to keep the Cosmological constant

    A positive value for the cosmological constant was found by the studies of Adam G. Riess et al and Pearlmutter et al In terms of Planck units, and as a natural dimensionless value, the cosmological constant, λ, is on the order of 10−122 or 10−29 g/cm3 The cosmological constant has negative...
  14. N

    No Inflation in Brane Cosmology: Is Dark Energy the Driver?

    In brane cosmology how can there be no such thing as inflation. I was watching a lecture with Neil Turok and he said he made a bet with Hawking that says that the new Planck satellite will give us information that could prove against inflation. So, my question being, instead of inflation in the...
  15. K

    Unifying Dark Energy & Dark Matter: Investigating the Chaplygin Gas

    Hello every one! How many of you have learned about the unification of dark energy and dark matter? I'm doing my research regarding the Chaplygin gas and I've come across this research paper. arxiv.org/pdf/grqc/0202064.pdf At the end, they solve the equation 36 (3/2*ab′′ + (1 − w)ab′ −...
  16. A

    Dark energy, matter in a Multiverse Schemata

    Dark Energy is the term used for the energy / quanta that is required to fill our space. If we considered that our space contained multiple universes, we would need between 75 and 85 universes of the same size as our own to fill our space. I think this would be satisfied if our space is a 3-D...
  17. M

    Dark Energy: Questions on Uniform Energy Density

    About a week ago at campus, we had a colloquium on dark energy. I have been studying it some, and a couple of things are bothering me. Perhaps someone can help :) My worry comes from the idea of uniform energy density. As I understand it, this can be explained either as truly uniform -...
  18. C

    Are dark energy and dark matter the same?

    Someone said that they are by mass-energy equivalence. Also, is it possible to say that dark matter is a indeed a form of matter, and dark energy is a form of energy?
  19. M

    Dark Energy: Big Bang, Big Crunch & Expansion

    Is the reverse of big bang that is big crunch likely to happen??or will dark energy dominate the gravity and the space will coninuoisly expand?
  20. L

    How well has the force of Dark Energy been calculated?

    What i would like to know is, how far apart would 2 masses of 1kg each have to be, for the effects of their gravitational attraction to be overcome by the force of the Dark Energy (i.e. to begin moving away from, rather than toward one another?) The basic question I am trying to pick away at...
  21. T

    A Very Good Resource on Dark Energy

    Dark Energy - a Pedagogic Review http://arxiv.org/abs/astro-ph/0409166
  22. W

    Tap Dark Energy for Energy Needs: Ideas and Questions

    Any thought about tapping Dark Energy to meet our energy requirements?
  23. B

    Dark Energy: Does It Affect All Space?

    Does dark energy only affect space between galaxies? Or does it appear anywhere there is space? For example Between the Earth and the sun? Also on even smaller spaces like between a nucleus and an electron?
  24. 7

    Dark Energy in the Zero Energy Universe

    Hello~ I’m sorry. I can’t English well. 1. Assuming that total energy of universe is zero. It looks more natural when an initial energy value of universe is 0. Therefore, negative energy is needed to offset positive energy of matters. E_T = 0 = ( + E) + ( - E) = 0 2. Mass-energy...
  25. A

    Dark energy <=> negative energy?

    Sorry if this sounds a bit mixed up. When I was growing up, in the late 1990's, popular science books about cosmology use to describe the average mass-energy density of the universe, especially comparing it to the critical density. Those books used to say that visible matter gives too-low...
  26. E

    Can a Particle with Repulsive Properties Explain Dark Matter and Dark Energy?

    If it existed a particle that had such properties that it both pushed away other particles of the same kind and it pushed away ordinary matter ,could this then explain dark matter and dark energy ? If the big voids of the universe was filled with such a particle, the net force of the particles...
  27. C

    Dark Energy & Expansion of the Universe; Really ?

    Based on what I've gleamed from a couple NOVA type TV programs, it would appear based on our observations that all galaxies are moving away from us and each other at an accelerating rate. From what I can tell we infer the relative speed of galaxies based on observed light frequency shift which...
  28. E

    What makes Dark Energy cause Acceleration of the Expanding Universe?

    According to Misconceptions about the Big Bang in Scientific American by Charles H. Lineweaver and Tamara M. Davis, space-time is expanding and carrying galaxies with it, rather than galaxies being moved ever faster and further into space-time. See...
  29. wolram

    Can Mic Oscillations Replace Dark Energy in Cosmic Expansion Models?

    mic oscillations. [45] arXiv:1111.0520 [pdf, ps, other] One explanation for the acceleration of the universe's expansion Dong-Biao Kang Comments: 5 pages, 2 figures, 1 tables Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO) We have observed the...
  30. J

    Could dark energy simply be gravitational field energy?

    Could dark energy simply be gravitational field energy? If we assume that the Universe is always spatially flat then we have the equation: H(t)^2 = 8 Pi G rho(t) / 3 where H(t) and rho(t) are the Hubble constant and total matter density at time t. Now we have the equation c = H(t)...
  31. D

    I have a crude understanding of dark energy and the relativist universe.

    Hi there:), I've always been interested in the notion of an expanding universe. It seems like such a hand wavey thing to say. Over the past few years of my life I've done some thinking (with minimal scientific backing) about how and why the universe expands. I've come up with some pretty...
  32. T

    Arto Annila - Universe's expansion may be understood without dark energy

    http://www.physorg.com/news/2011-10-supernovae-universe-expansion-understood-dark.html Your input, please!
  33. R

    Programs Degree for studying Dark Matter and Dark Energy

    Accidently Posted this in the career guidance section earlier. Thought I should put it where its supposed to go. I am currently a physics major in my sophomore year of college. I have found that my interest really lies in Space, specifically Dark Matter and Dark Energy. Talking to a couple...
  34. A

    Formula for the dark energy density (dark energy formula)

    I propose a formula for the dark energy density (dark energy formula): ΩΛ = ΩbAeh/t2 In this equation: ΩΛ is the dark energy density, with the estimated value from 0.712 to 0.743, according to WMAP seven-year data release [1]; Ωb is the baryon density, 0.0456 ±0.0016, according to WMAP...
  35. G

    Is Dark Energy Necessary for the Acceleration of the Universe's Expansion?

    If the mass of the universe is constantly being converted to energy through nuclear fusion, and nothing can travel outside of space-time, then isn't the ratio of energy to mass increasing? If so, then wouldn't the only possible option be for an acceleration of the universe's expansion?
  36. H

    Nature of Dark Energy and a cracker in the sand

    I have a question of sorts. I was taught that the universe formed from the Big Bang, which was a unique event. Much later I learned about the hypothesis of a multiverse, and the prospect that the Big Bang and our universe might not be as unique. This has off course has yet to be proven. Later...
  37. V

    Effects of dark energy on our solar system

    Is there any effect of expansion of world on our solar system? i.e. Is there any change in distance between Earth and sun due to expansion of world?
  38. H

    Electro-Gravity ideas, Dark Energy

    Hello all, I know that there has been much work on the unification of gravity and electromagnetism, but I was wondering if they could be united the same way that electricity and magnetism were united- a changing gravitational field creates an electromagnetic field, and a changing...
  39. S

    Dark Energy, Dark Matter, and Empty Space

    Dark Energy, Dark Matter, and "Empty Space" I'm new to this forum, and I've looked around but did not find this discussed. Apologies if I missed it. Has anyone in the research of Astrophysics considered the "missing mass" of the Universe to be contained in the structure of space-time itself...
  40. G

    Unveiling the Mystery of Dark Energy

    What is dark energy? What is it composed of?
  41. T

    Dark energy - Expansion of the universe

    Hi everyone! Could you explain me how is the dark energy related to the expansion of the universe?? Thanks!
  42. C

    The Force of Space: Dark Energy and Its Impact

    Quick question - Is it that the bigger the space in between two bodies makes bigger room for more dark energy to allocate more force, making the two bodies distant of each other faster than the bodies such as me and my friend standing a meter away from each other?
  43. T

    Exploring the Possibilities of Dark Energy and Its Effect on Gravity

    I have a question and/or a thought on dark energy. I have just 2 years of college Physics so I apologize if my question seems stupid. However, I was thinking about dark energy and the weakness of gravity relative to the other forces and the idea of living in a finite universe. Then I read an...
  44. P

    Exploring Dark Energy: Resources & Topics

    hi i want some help about the dark energy beacuse i need to write aresearch about it so can you lead me to good references that i can back to and what are the measure topics that i can talk about thanks
  45. L

    Matter creation, dark energy, and the possibility of a Big Crunch

    Hi physicsforum members, I am currently in a discussion with a fellow traveler on the chances of a Big Crunch. To my knowledge, it's a long shot. But to him it is the accepted mainstream view on the "ends" of the universe. Before I get to my question, I have to provide some back story (I...
  46. S

    Is LQC compatible with dark energy?

    Does LQC have anything to say about dark energy? Ive heard a few poeple says LQC is inconsistent with dark energy but that seems wrong to me. I think they are confusing it with Tollman ossiclating universes. As I understand the bounce in LQC only tell us that our universes had a prior...
  47. N

    What is Dark Energy? New Discoveries and Implications

    "Nothing new under the sun"? Dark Energy Is Driving Universe Apart: NASA's Galaxy Evolution Explorer Finds Dark Energy Repulsive (Purists can freak about dark energy being represented separately, and apparently flat, from spacetime in the accompanying diagram. )...
  48. I

    Is Dark Energy Propelling the Accelerating Expansion of the Universe?

    Hi all, I would like to share this interesting article : http://www.bbc.co.uk/news/science-environment-13462926" Einstein was right , does this mean we have confirmed the existence of some 74% our universe but not sure of the whole mechanism ? EDIT:I was just discussing about this discovery...
  49. phinds

    Puzzled by new confirmation of dark energy

    puzzled by "new" confirmation of dark energy Just saw an article on BBC: http://www.bbc.co.uk/news/science-environment-13462926 that says they have used a new technique to confirm the existence of dark energy. I don't know enough to understand why what they did is "new", as I am sure I...
  50. cepheid

    News Article + Paper on Dark Energy

    Does anyone know what paper this news article is referring to? http://www.cbc.ca/news/technology/story/2011/05/19/science-dark-energy-einstein-blake.html I'm thinking it must be this one, http://arxiv.org/abs/1105.2862 but what the paper is saying and the way the article is...
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