Cosmological constant Definition and 188 Threads

So CMBR points to a flat universe, and this seems to be the generally accepted model. But in a flat universe is expansion not supposed to slow exponentially, stopping after an infinite time? How does this fit with the observation that distant type Ia supernovae show the universe's expansion to...

Layman here, please excuse my ignorance. I believe to understand the basics of SR, GR, cosmic expansion, etc but questions come to mind now and then. As I understand, dark energy, the cosmological constant, vacuum energy, whatever you may call it, remains a constant per space volume unit. Empty...

This Invited Review article just came out: http://arxiv.org/abs/1603.08658 The Atoms Of Space, Gravity and the Cosmological Constant T. Padmanabhan (Submitted on 29 Mar 2016) I describe an approach which connects classical gravity with the quantum microstructure of spacetime. The field equations...

Homework Statement (Working with geometrised units) Consider the EFE ##G^{\alpha \beta }+\Lambda g^{\alpha \beta} = 8 \pi T^{\alpha \beta} ## work out (using weak-field considerations) an upper bound for the cosmological constant knowing that the radius of Pluto's orbit is 5.9 x 10^12 m...

When we measure the cosmological constant Λ what we are really doing is measuring the longterm value of the Hubble rate, namely H∞, the distance expansion rate that the present rate H(t) is seen to be declining towards and leveling out at. It's convenient to write distance expansion rates as...

Piran et al., "Cosmic explosions, life in the Universe and the Cosmological Constant," http://arxiv.org/abs/1508.01034 I thought this was interesting. If I'm understanding correctly, the idea is that satellite galaxies such as the Magellanic Clouds have low metallicity, which causes them to...

Could anyone please recommend a paper that accurately gives the value of the cosmological constant? Or else may you reply with values of the cosmological constant that you would you use in your research? Any help would be very much appreciated.

How come that, in the context of discussing the search for gravitational waves, I never see the cosmological constant mentioned ? We know that ##\Lambda \neq 0##, so this seems strange to me; in the presence of a non-vanishing constant, the background is not Ricci flat in the vacuum case, so...

I understand that in order to preserve the inner product of two four vectors under a change of coordinates x^{\mu}\rightarrow x^{\mu^{'}}=\Lambda^{\mu^{'}}_{\,\, \nu}x^{\nu} the Minkowski metric must transform as \eta_{\mu^{'}\nu^{'}}=\Lambda^{\alpha}_{\,\...

Fellow Nerds, I'm looking for a quantitative relationship between the gravitational strength of a point on a field and the speed of expansion of space at that point. Given a cosmological constant and a metric, is it possible to pinpoint a certain point of space and ask how quickly that space is...

http://physics.princeton.edu/~steinh/lambda16.pdf In this research article the authors suggest a cyclic universe, specifically one involving collisions of higher dimensional branes (an idea taken out of string theory), could indirectly explain why the observed cosmological constant is so small...

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...

In the EFE, what does adding Λgμν mean and why is it not included in the Einstein tensor?

Hello! me and my friends were discussing a few ideas earlier this week and then we suddenly started talking about Einstein's biggest mistake. I was a bit lost because I am not all that familiar with the Cosmological constant and I was wondering how can probability be applied to that mistake?? I...

Hello everyone. I am having some problem with dark energy and the cosmological constant. The cosmological constant is a proposed form of dark energy. Alright, now the cosmological constant is is estimated by cosmologists to on the order of 10^-26 kilograms per cubic meters. But the density of...

In one book of Susskind I found the following claim and I wanted to ask for its basis. Susskind says that each kind of boson gives positive contribution to the cosmological constant (the lighter, the better). Each kind of fermion gives negative contribution to the cosmological constant. Thus...

For instance our quantum vacuum has a certain Cosmological constant and the question is can there be other vacuums with different values and if so where's the evidence for this I would like to read it. How do you derive the Cosmological Constant through something like Quantum field theory or...

I read a article now and It claims he found the cause of cosmological constant.Is that true ? The idea is actually good...

I am trying to wrap my brain around the idea of the cosmological constant, and how it gives the result of an accelerating universe. I have read different explanations for it, and in some it gives me the impression that it is an actual physical force, pushing everything away from everything...

Hi. I was just curious about the current value of the cosmological constant. My astrophysics class lecture notes say on the order of 10^-122, but the Wikipedia article says 10^-35 s^-2. Could someone explain where the 10^-35 s^-2 value comes from? Thanks!

Why cosmological constant term ##\Lambda g_{uv}## in Einstein equation is proportional to ##g_{uv}##. Why it is even proportional to ##g_{uv}## in spacetime of MInkowski?

In this thread, I would like to discuss: "which is more natural for a simple cosmological model: taking the long term Hubble time as a timescale (as Marcus has done), or taking the Hubble time as a timescale". I will start by paraphrasing Marcus' OP and replacing his '##\Lambda##-timescale' with...

Homework Statement (a)Sketch how the contributions change with time (b)For no cosmological constant, how long will this universe exist? (c)How far would a photon travel in this metric? (d)Find particular density ##\rho_E## and scale factor (e)How would this universe evolve?[/B] Homework...

What is the cosmological constant for the Godel metric?

Is space time has a energy itself ? Thanks

I reading book, part about gravity. It is Landau-Lifschiz, "Theory of field". And I trying to understand how to calculate cosmological constant. Re-read part with introduction of cosmological constant several times, still not understood. Let's imagine function of space curvature, without...

I was reading a book about cosmolgy.And there wrotes vacuum energy must be higher than cosmological constant 10100 times to satisfy (It may just the opposite ) observations. Is that true ?

So the Universe expanded very rapidly in its very first moments (inflation). The Universe then slowed down and is speeding up again, and Dark energy is supposed to be responsible for this accelerated expansion. The cosmological constant might as well be dark energy, but why is it still being...

Simplistically, the GR equation is G = k T + l g G represents the curvature of the fabric of space-time T is the stress energy tensor, representing the fluxes and densities of matter and energy g is the metric tensor So... In another thread, someone said that the cosmological constant...

So Einstein Equation: ##G_{uv}= 8 \pi G T_{uv} ##, Justifying the cosmological constant can be included is done by noting that ## \bigtriangledown^{a}g_{ab} =0 ## and so including it on the LHS, conservation of energy-momentum tensor still holds. I'm not sure why ## \bigtriangledown^{a}g_{ab}...

...through inertial mass, namely to explain away the sameness of inertial and gravitational mass? If you assume that only inertial mass is a "real" effect, then gravity would simply become a fictious force arising from inertial mass holding matter back from expanding alongside spacetime during...

Homework Statement For the equation H^2 = \frac{8 \pi G \rho_m}{3} + \frac{H}{r_c} how do I find the value of H for scale factor a \rightarrow \infty , and show that H acts as though dominated by \Lambda (cosmological constant) ? Homework Equations \rho_m \propto \frac{1}{a^3} H > 0...

The title says a lot about my doubt. I don't know a lot about inflation maths but the idea is that in Inflation, I am seeing that the Cosmological Constant (ie Vacuum Energy) is not Constant in two ways: 1 With time; the Vacuum Energy was larger in the beginning and that triggered Inflation...

Homework Statement Give q(t) the deceleration parameter, as a function of: \Omega_{\Lambda}, the cosmological constant density, and \bar{a}(t) = \frac{a(t)}{a(t_{0})}= 1+ H_{0} (t-t_{0}) - \frac{1}{2} q_{0} H_{0}^{2} (t-t_{0})^{2} where a's the scale factors have already defined τ =...

Hi Everyone! I need a bit of help with the following question please. How does the energy density of the cosmological constant Uλ=ρλc^2 have the required SI units if λ=4∏Gρ/c^2 I know that the energy density of the cosmological constant (Uλ)is essentially dark energy and the SI units...

Suppose the energy density of the cosmological constant is equal to the present critical density ε\Lambda = εc,0 = 5200 MeV m-3. What is the total energy of the cosmological constant within a sphere 1 AU in radius? My answer: ε\Lambda = ET / V ET = ε\Lambda * V = (8.33 * 10-10...

Are dark energy and the cosmological constant the same thing?

The PF home page has some news items in the righthand margin and one is about this: http://arxiv.org/abs/1404.1801 The popular news account is this BBC piece: http://www.bbc.com/news/science-environment-26329320 "They find that some three billion years after the Big Bang, the cosmos was...

Hi, I have some confusion about the cosmological constant (CC). From what I have read it is to do with the energy density throughout the entire universe which is thought to drive the expansion of the universe. If the CC were any smaller then matter would not have been able to form and since the...

I have a question about GR in a cosmological setting. If dark energy is assumed to be a true GR cosmological constant, does this require some kind of energy input. I am curious to know if this is just a 'curvature' of space somehow, or does it represent a continual addition of energy on some...

The bare cosmological constant in field theory is needed to cancel the infinite vacuum zero-point energy. Then you get a renormalized cosmological constant. There are three quantites at play, Ω=E+Ω0, where E is the infinite vacuum zero-point energy, and Ω is the renormalized cosmological...

I'm confused about the relationship between two seemingly different concepts of flatness of the universe. 1. Spatial flatness. This is the lack of any curvature on a large scale. Simple enough... 2. Energy density flatness. If the energy density is higher than a critical value, then the...

The cosmological constant (Ʌ ) is equated to dark energy and has units of energy/volume. Why have I read that Ʌ equals the Hubble constant squared (H2) which has units of 1/sec2? There must be an obvious explanation.

The vacuum-vacuum expectation value in the absence of a source is in general not equal to 1, but exp[-iEt], where E is the energy of the vacuum. For some reason in QFT, we say E=0 (i.e., we normalize Z[0]=1, the generating functional), but we don't need to do this and one can in fact calculate E...

Since Omega-lambda is very close to Omega-matter, what could it mean if we assume they are exactly equal to each other. Also, let's assume they were always equal since coincident problem is unnatural.

I have always wondered about how cosmological constant is characterized. You often read the “cosmological constant measured to be ….”.So since it is still a hypothesis, shouldn't the statement read “cosmological constant calculated to be ….” . Or Is it that such semantics does not matter.

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...

Padmanabhan is guilty of another interesting paper - Solution to the cosmological constant problem, http://arxiv.org/abs/1302.3226. Any thoughts?

reading these new jacobsen papers, yesterday. a few questions came up Does Jacobsen tries to solve Cosmological constant problem with these papers ? http://arxiv.org/pdf/1212.6821.pdf

I can fairly well grasp the trace relationship between the Einstein tensor and the Ricci tensor, and see that Ricci tensor is a multiple of the metric. If the cosmological constant is included I don't get why the Einstein tensor shouldn't become a multiple of the metric (leaving out physical...