Questions tagged [cosmological-constant]
The cosmological constant is the energy density of space, or vacuum energy, that arises in Albert Einstein's field equations of general relativity. It is closely associated to the concept of dark energy, but, according to quantum field theory, it should also account for all the zero-point energies of quantum fields in space.
417
questions
1
vote
1
answer
62
views
Cosmological Constant Problem calculations involving energy densities
I am following Timo Weigand lecutre notes on QFT, on page 28, he breifly touches on the Cosmological Constant Problem.
But I am a little confused.
He begins with a Lagrangian and include a nonzero $V_{...
- 413
0
votes
0
answers
18
views
What is the formalism for calculating the vacuum energy density from the observed data of the expansion of the universe?
Wikipedia states here the calculated effective vacuum energy density value of free space from the observed and collected cosmological constant data of the 2015 Planck telescope satellite mission. But ...
- 3,728
5
votes
2
answers
179
views
Properties of anti-deSitter space
I have some questions about anti-deSitter space, (note: I am not a physicist)
When describing deSitter space it is almost always mentioned that it has a positive cosmological constant and is therefore ...
- 191
2
votes
1
answer
78
views
DeSitter cosmological horizon stability?
If the universe keeps expanding at an accelerated rate (given by the cosmological constant) then the universe would approach a DeSitter spacetime where there would be a cosmological horizon that would ...
- 1,810
0
votes
1
answer
40
views
Is AdS repulsive?
Is Anti de Sitter spacetime repulsive because of its negative scalar curvature? Will a fluid flowing radially inward experience an opposition that has a radially outward component? And how can one ...
- 535
2
votes
0
answers
40
views
Textbooks on the Schwarzschild-de-Sitter Metric
Does anybody know a textbook on the geometry of the Schwarzschild-de-Sitter metric and its maximal extension? It's not in Hawking & Ellis.
1
vote
1
answer
69
views
Whether vacuum energy gravitate?
What is the relationship between vacuum energy and gravity, particularly in terms of gravitational effects and its contribution to the overall cosmological constant? Does vacuum energy possess ...
2
votes
2
answers
262
views
How to "naively" calculate the vacuum energy density in a $4 + d$ spacetime?
The "naive" calculation of the vacuum energy density in flat 4D spacetime is resumed by the following divergent integral (I'm considering only free massless fields):
$$\tag{1}
\rho_{\text{...
- 7,023
0
votes
0
answers
32
views
Is an $R \sim O(T^2)$ acceleration of expansion of the Universe possible based on data?
We currently assume based on observations that the expansion of the Universe is accelerating. Now this can mean a lot of things, but for some reason it is always described as an exponential ...
-3
votes
1
answer
80
views
Can matter and light exist without the free space absolute vacuum?
According to the standard model of particle physics, is matter and light possible to exist without the existence of the omnipresent vacuum?
By "vacuum" here I mean the ideal perfect vacuum ...
- 3,728
2
votes
2
answers
92
views
How the EM energy-momentum tensor of vacuum state could be proportional to the metric?
We read "everywhere" that, because of Lorentz invariance, the energy-momentum tensor of any field in the vacuum state should reduce to a constant multiplying the metric tensor (I'm using the ...
- 7,023
0
votes
0
answers
23
views
How to calculate escape velocity of timelike particles in Schwarzschild Anti de Sitter spacetime?
From the geodesic equations, we can form something like
$$\dfrac{1}{2}\left(\dfrac{d r}{d\tau} \right)^2 +V_{\text{effective}} = \tilde{E}$$
Since $\tilde{E}>0$ will correspond to unbound orbits, ...
- 535
1
vote
0
answers
35
views
Analytic expression for a universe without a big bang [duplicate]
I was reading introduction to modern cosmology by Andrew Liddle. On page 56 he shows a graph of the $\Omega_{\Lambda}$, $\Omega_{0}$ plane and there's a region where no big bang is needed, later on ...
0
votes
0
answers
37
views
What exactly do astrophysicists mean when they say that the universe is expanding at an accelerated rate? [duplicate]
What exactly do astrophysicists mean when they say that the universe is expanding at an accelerated rate? Assuming that the universe is a sphere, do they mean that the radius of the universe increases ...
- 35
0
votes
0
answers
39
views
How do different vacuum energies cancel out?
I've heard that the predicted vacuum energy by quantum mechanics is way far away from what we can actually calculate according to general relativity. The current patch is to include a cosmological ...
- 503
1
vote
1
answer
49
views
Reference: 1+1D paper-model representation of the Lambda-CDM cosmological model
I'm looking for a 1+1D (1 time + 1 space dimension) paper model of the current $\Lambda$CDM cosmological model; if possible, one which somehow respects the scales of geodesic spacelike distances at ...
0
votes
0
answers
67
views
How can we use CMB to measure the value of the cosmological constant?
Another mystery facing cosmologists is the accelerating expansion of the universe. In 1929, astronomer Edwin Hubble showed that the universe was expanding, but for this expansion to be justified, ...
1
vote
0
answers
37
views
In the $\Lambda$CDM model, is the cosmological constant always interpreted as the vacuum energy contribution?
As in the title, in the $\Lambda$CDM model, is the cosmological constant always interpreted as the vacuum energy contribution? Or is the origin left open?
If I say that "it is usually ...
- 299
0
votes
1
answer
45
views
Why the Hubble parameter that is proportional to dark energy is squared in the Friedmann's equation?
I'm studying Alexander Friedmann's equation about the Hubble parameter and, thus, the time dependence of the cosmic scale factor varies as the matter density, ρ, and as the dark energy, Λ as shown in ...
- 71
3
votes
1
answer
464
views
Confusion regarding the cosmological constant
The value of the cosmological constant is:- $+2.036\times 10^{-35} ~\mathrm{Hz}^2$. What does it mean about the characteristics of our spacetime? What does the value of the cosmological constant tell ...
- 836
4
votes
1
answer
152
views
The energy conditions and cosmological constant?
So I thought it didn't matter which side of the equation the cosmological constant was one (did it emerge from geometry or the stress energy tensor). However, then I remembered the weak , strong, null,...
- 1,221
5
votes
1
answer
621
views
What does it mean for a black hole to be "filled" with vacuum energy?
I've read the recent news about non-Kerr black holes coupling to the universe's expansion rate, and it looks like an excellent fit to the data. From the paper, I understand that these black holes grow ...
- 278
1
vote
1
answer
121
views
How to move from AdS to dS space?
I studied different black holes in different spacetime and I also checked their differences, for example, the difference that exists in dS and AdS spaces. The question that has been created for me is ...
- 65
0
votes
0
answers
38
views
How can a cosmological constant exist in flat Minkowski Space?
The ground state energy of a standard scalar field in Minkowski space diverges so we need normal ordering to get it to zero. This divergence is normally interpreted as coming from the cosmological ...
2
votes
1
answer
74
views
Should the linearized field equations of GR with cosmological constant be gauge-invariant?
Say I have a solution to Einstein's field equations (EFE) with cosmological constant (CC)
$$
G_{a b}[g] + \Lambda g_{a b}=T_{ab}[g,\Phi]
$$
and want to find a perturbative solution $g_{a b} + \delta ...
- 21
1
vote
1
answer
80
views
By what experiment is the vacuum energy density actually measured?
I have heard that the actual vacuum energy density which is up to 120 orders smaller than the predicted QED value can be measured in experiments or cosmological observations?
What are these ...
- 3,728
2
votes
0
answers
43
views
Why no cosmological constant in momentum constraint?
In the ADM formalism of general relativity, one decomposes the Einstein equations in (3+1) dimensions. More explicitely, if the Einstein equations are given by
$$R_{\mu\nu}-\frac{1}{2}Rg_{\mu\nu}+\...
- 824
3
votes
3
answers
341
views
Cosmological constant from the stress energy tensor or geometry?
Sabine does make some interesting points. Can a cosmological constant come from the stress energy tensor? If so, I don't see how one is suppose to distinguish this as an all permeating field in the ...
- 1,221
2
votes
1
answer
54
views
How can we measure cosmological constant if we can't measure ground state energy?
From what I understand, we can only measure energy differences (see for example Peskin & Schroeder page 21, last paragraph), and therefore the ground state of a system cannot really be measured.
...
- 690
2
votes
1
answer
89
views
Existence of any vacuum pressure
We know that there exists an underlying background energy in space throughout the entire Universe, called vacuum energy and this is a special case of zero-point energy that relates to the quantum ...
- 684
1
vote
0
answers
53
views
What IS the energy density of vacuum space (or spacetime)? [duplicate]
The question, even if similar to other questions here, pretends to clarify a subtle question: the identity of vacuum energy (or energy-density being more precise).
Should we be confident in the ...
- 6,327
1
vote
0
answers
70
views
Corrected Poisson's equation and the preferred time direction of the cosmological constant? [closed]
So if I correct (equation 2.6) the Poisson's equation with the cosmological constant. Then, I get
$$ \Delta \Phi = (4 \pi G_N) \rho - \Lambda \tag{1}$$
But when I think of this from the Einstein-...
- 1,221
1
vote
0
answers
51
views
Expansion of the Universe inside mattar [duplicate]
When talking about the expansion of the universe we usually refer to the Friedman equations so we assume homogeneous and isotropic solution to Einstein field equation which is true on cosmological ...
- 1,638
1
vote
0
answers
28
views
The General form of the Friedmann equation written in another way
Using the general form of the Friedmann equation:
$$H^2 =H_0^2(Ω_{m0}(1+z)^3+Ω_{r0}(1+z)^4+Ω_{k0}(1+z)^2+Ω_Λ)$$
and taking $a_0=1$, How can I derive that the Friedmann can be writing in the following ...
- 11
2
votes
0
answers
95
views
What's wrong with this thermodynamics argument on the cosmological constant?
I'm puzzled by the following thermodynamics argument on the cosmological constant interpreted as a perfect fluid of pressure $p = -\, \rho$. I start considering a simple fluid of local energy density ...
- 7,023
1
vote
2
answers
118
views
Why does $\Lambda>0$ violate SEC (Strong energy condition) in GR
We stated during lectures (without any further explanation) that existence of positive $\Lambda$ (cosmological constant) violates strong energy condition (SEC). I am trying to figure out where this ...
- 966
0
votes
1
answer
89
views
The extreme dS black holes in 5 dimensions
In the paper https://arxiv.org/abs/hep-th/0401192, we have a $f(r)$ in Eq(6).
$$f(r)=1-(\Lambda/3)r^2-M/r^{(D-3)}+Q^2/r^{2D-6}$$
In 5 dimension $f(r)$ is
$$f(r)=1-(\Lambda/3)r^2-M/r^2+Q^2/r^{4}$$
For ...
- 65
2
votes
1
answer
77
views
Ultrastatic spacetime and cosmological constant
A spacetime $(\mathcal{M},g)$ is called "ultrastatic", if it admits a set of coordinates such that
$$g=-\mathrm{d}t^{2}+h$$
where $h$ is a Riemannian metric, which does not depend on time. ...
- 824
2
votes
1
answer
133
views
Static Spacetime = no cosmological constant?
I stumbled over a strange result, which cannot be true: In the (3+1)-formulation of general relativity, one considers a metric of the type
$$g_{\mu\nu}\mathrm{d}x^{\mu}\mathrm{d}x^{\nu}=(-\alpha^{2}+\...
- 824
2
votes
1
answer
186
views
Cosmological constant term in Newtonian gravity [duplicate]
Recently, I came across something I found quite interesting on Wikipedia, which is the addition of the cosmological constant to Newtonian gravity. The Wikipedia page (Alternatives to General ...
- 343
4
votes
2
answers
184
views
Is Hubbles law due to Gravity?
Hubble's law states that Distance is proportional to Velocity. A ScienceDirect article states that Classical Hubble expansion is characterized by a proportional increase in the rate of expansion ...
user348071
0
votes
0
answers
36
views
Could a CPL (Chevallier-Polarski-Linder) parametrization be included in Brans-Dicke model?
I have studied up to now about forecasts to constrain cosmological parameters in the context of CPL( Chevallier-Polarski-Linder ) parametrization with $w_0,w_a$ parameters in equation of state for ...
user87745
1
vote
0
answers
37
views
Brans-Dicke theory: could a negative value for $\Omega_{BD}$ mimic a current acceleration of expansion like in LCDM model
I am working on Brans-Dicke models, in the simplest form (without cosmological constant) and the other form (with cosmological constant)
I am trying in both cases to estimate by MCMC the different ...
user87745
2
votes
0
answers
51
views
ADM equations with cosmological constant
Does anyone know a reference in which the ADM equations for general relativity (the equations for the spatial metric and conjugate momentum or extrinsic curvature using the lapse and shift in the 3+1 ...
0
votes
1
answer
127
views
Models in which the vacuum energy gravitates on small scales but not on large scales
Are there models in which the vacuum energy gravitates on small scales but the effect is diluted on large scales?
- 43
2
votes
1
answer
57
views
Deviations of conservation laws in the context of cosmological evolution?
If energy is "not conserved" in General Relativity (or at least, it is difficult to define it) in the context of an expanding accelerating spacetime (like it happens in our Universe), are ...
- 1,810
1
vote
0
answers
74
views
Cosmological constant of $\text{AdS}_5 \times S^5$
I have a quick question about the Einstein-Hilbert action $S_{\text{EH}}$ action with cosmological constant regarding $\text{AdS}_5 \times S^5$ spacetime. $S_{\text{EH}}$ is given by
$$S_{\text{EH}} = ...
- 368
1
vote
1
answer
83
views
Complex Cosmological constant
Does a complex cosmological constant ($\Lambda = a + ib,\quad b\neq 0$) exist? If it does exist, what does it represent physically?
For example, we interpret $\Lambda > 0$ as dS space and $\Lambda ...
- 45
0
votes
1
answer
98
views
Can the universe break like a balloon that pops?
I have been investigating inflation and the big difference in the theoretically predicted value of the cosmological constant and the actually measured value of it. There would be 120 orders of ...
- 55
6
votes
3
answers
390
views
Approximation for Newton's formula for gravity as modified by the expansion of the universe?
Newton's formula for the gravitational force between two objects is
$$F = -\frac {Gm_1m_2}{r^2}.$$
Assuming the force is due to the exchange of gravitons and that gravitons are affected by the ...
- 2,343