What is Accelerated expansion: Definition and 27 Discussions

Observations show that the expansion of the universe is accelerating, such that the velocity at which a distant galaxy recedes from the observer is continuously increasing with time.The accelerated expansion was discovered during 1998, by two independent projects, the Supernova Cosmology Project and the High-Z Supernova Search Team, which both used distant type Ia supernovae to measure the acceleration. The idea was that as type Ia supernovae have almost the same intrinsic brightness (a standard candle), and since objects that are further away appear dimmer, we can use the observed brightness of these supernovae to measure the distance to them. The distance can then be compared to the supernovae's cosmological redshift, which measures how much the universe has expanded since the supernova occurred. The unexpected result was that objects in the universe are moving away from one another at an accelerated rate. Cosmologists at the time expected that recession velocity would always be decelerating, due to the gravitational attraction of the matter in the universe. Three members of these two groups have subsequently been awarded Nobel Prizes for their discovery. Confirmatory evidence has been found in baryon acoustic oscillations, and in analyses of the clustering of galaxies.
The accelerated expansion of the universe is thought to have begun since the universe entered its dark-energy-dominated era roughly 4 billion years ago.
Within the framework of general relativity, an accelerated expansion can be accounted for by a positive value of the cosmological constant Λ, equivalent to the presence of a positive vacuum energy, dubbed "dark energy". While there are alternative possible explanations, the description assuming dark energy (positive Λ) is used in the current standard model of cosmology, which also includes cold dark matter (CDM) and is known as the Lambda-CDM model.

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  1. SH2372 General Relativity - Lecture 10

    SH2372 General Relativity - Lecture 10

    0:00 Cosmological redshift 18:08 Solving the Friedmann equations 34:34 Accelerated expansion and the cosmological constant 56:10 Cosmological inflation
  2. C

    B No way to catch up with galaxies currently receding at >c?

    Consider a far-away galaxy that is considered to be currently receding from Earth at 2x the speed of light. (With this 2x c recession velocity, we are speaking of the Vnow, the imputed relative velocity of the galaxy compared to Earth now, not the velocity of the galaxy relative to Earth at the...
  3. E

    B The accelerated expansion of the universe; redshift and time/distance

    I am certain that my confusion here rests in a misunderstanding on my part and not in a mistake having been made by countless physical theorists. Nevertheless, I have had a hard time wrapping my head around it. Here is the crux: We observe that light from distant objects is more redshifted...
  4. O

    I Universe expansion discrepancy vs accelerated expansion

    Hi! Obviously my understanding is at a pretty elementary level, but nevertheless I'm puzzled by the reaction of astronomers and astrophysicists to the discrepancy in the measurements of the expansion of the early universe based on the Cosmic Microwave Background, and the measurements of its...
  5. D

    B Accelerated expansion of the universe

    If a big bang could occur at a point in space-time, couldn't we at least speculate that many big bangs could have occurred at many other points in space time, and could have resulted in many parrelel universes evolving far away or in close neighborhood of our own one? And then, could it not be...
  6. M

    B Where Was Dark Energy Before the Accelerated Expansion Began?

    Before the period of the the accelerated expansion started about 5 billion years ago.. where was the dark energy and what was it doing. Or could it only got produced 5 billion years ago and non-existent before that?
  7. Bolhuso

    I Where did the Dark Energy (or similar mechanism) come from?

    Hi all! I'm new to this forum and, as a matter of fact I only recently rediscovered my interest for physics. I am starting to catch up, yet I find that Wikipedia sometimes falls sort for some basic questions, and I was hopping that this community could gently help me understand some concepts...
  8. P

    B Are inflatons the same as fewer gravitons?

    I'm not very conversant in the subject. But it is my impression that the acceleration of the expansion of the observable universe has generated a theory that there might be a new particle (field?) call the inflaton. On the other hand, I thought I'd heard that scientists were trying to find...
  9. e2m2a

    A Inertia & Accelerated Expansion: How Does Machian Explanations Fit In?

    I understand that some old Machian interpretations of inertia require a closed universe. Now that it has been confirmed that the universe is expanding forever and is not closed, how does Machian explanations of inertia fit in with this?
  10. G

    I Accelerated expansion and Hubble plot

    Hello! I have a question regarding the effect of the accelerated expansion of the universe on the Hubble plot (redshift over luminosity (or distance). I understand that for relatively nearby galaxies, this appears to be a linear relationship but that because of the accelerated expansion of the...
  11. S

    Accelerated expansion and perceived gravity

    Since the universe is expanding at an accelerated rate and accelerating frames can perceive that motion as being the result of a gravitational field, have we ever been able to sense a gravitation field fluctuation in the Earth that occurs every 24 hrs? Would someone not be facing the direction...
  12. R

    Alternative hypotheses regarding dark energy?

    Currently, the favoured explanations for the accelerating expansion of the universe are the cosmological constant, and various scalar fields, most notably quintessence. All of these are mechanisms dependent on mathematical field properties. My question is: do any alternative hypotheses exist...
  13. F

    Is accelerated expansion creating energy

    If the universe is accelerating in its expansion, and galaxies are increasing their speed away from each other, does that mean that the kinetic energy of the galaxies are increasing with the increase in the expansion rate? If so it would seem that the energy of the universe is increasing. Is...
  14. R

    Question regarding dark energy and accelerated expansion

    Question regarding dark energy and accelerated expansion. If gravitational force were somehow diminished at large distances----ie lower gravitational constant at huge distances--might this explain the increase or accelerated expansion seen. If this were true, would it be necessary to evoke a...
  15. MTd2

    Accelerated Expansion from Negative Λ

    I think this is one of those papers that will have millions of citations http://arxiv.org/abs/1205.3807 Accelerated Expansion from Negative Λ James B. Hartle, S. W. Hawking, Thomas Hertog (Submitted on 16 May 2012) Wave functions specifying a quantum state of the universe must satisfy...
  16. A

    Inflation and accelerated expansion of the universe

    Is it possible to relate the inflation of the universe in its early states with the current accelerated expansion of space-time?
  17. S

    Virtual particles and accelerated expansion

    In my textbook, "Universe" by Friedman et al it says the following: "During inflation, however , the universe expands so fast that particles were rapidly separated from their corresponding antiparticles. Deprived of the oppurtunity to recombine and annhilate, these virtual particles became real...
  18. W

    Accelerated Expansion of Space question

    I am in a heated debate about the laws of physics with someone who's sole answer to all of my statements has been "because god made it that way". Rather than get into that debate, I was wondering if folks could look over my hypothesis about why the universe is accelerating and point out the...
  19. TrickyDicky

    Accelerated expansion and lightcurves

    Is the time dilation associated to cosmological redshift that can be seen as a photometric slowing of the SNe Ia lightcurves directly related to the accelerated expansion seen on these same type of supernova from 1998? If not, what's the difference? Thanks
  20. L

    Does Hubble's law implies accelerated expansion?

    I`ve read that the universes expansion is accelerating. To explain this we have introduced concept of Dark matter and energy. However, Hubble's law: v = H*d means that a speed that separates two points is proportional to their distance. But since they are moving apart the distance becomes...
  21. P

    Accelerated expansion without Dark Energy?

    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...
  22. H

    Does the accelerated Expansion add credibility to Steady State Cosmology?

    Recently the expansion of the Universe has been found to accelerate. When studying Hoyle, Gold and Bondi's Steady State Cosmology, it clearly predicts an acceleration like this. I realize that this theory has been 'put to bed', and abolished, and all the other colorful language people like to...
  23. R

    Help wanted with accelerated expansion and gr

    When I first read about accelerated expansion in 1999 I immediatelly thought of gravitational repulsion between matter and antimatter. I know it is an old idea, and very much out of the mainstream, but when you read reviews about the arguments against it, it really makes you think. It is a case...
  24. Chronos

    Accelerated expansion revisited

    I was reading about this on Arxiv over the weekend and was about to start a thread here when I notice alexsok got the scoop on me in the 'Beyond the Standard Model' forum. So give him credit for 'catch of the day' for the link to http://physicsweb.org/articles/news/10/11/16/1 Here is the...
  25. daniel_i_l

    Exploring the Accelerated Expansion of the Universe

    I read that we've recently found that the universe is expanding at an accelerated rate by observing the fact that objects that are further away from us are redshifted more and thus going faster were: v = H*d were H is the rate that the universe is expanding. But if the universe is expanding...
  26. Chronos

    Accelerated expansion: is the jury still out?

    I thought this was interesting: High Redshift Supernovae: Cosmological Implications http://arxiv.org/abs/astro-ph/0502247 ... it appears that the problem of whether there is an acceleration in the Universe, and if so what its strength is, is not definitely solved and that much work is...
  27. K

    Accelerated expansion and its rate

    I am graduate student working now at the project in cosmology. I would appreciate any links or references to the papers or publications casting a light on the problem of accelerated expansion of the universe. Did they found the rate of accelerated expansion?