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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.

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Does the cosmological constant entail a mass for the graviton?

If I consider the Einstein equations into the form $$ R_{\mu\nu}=\kappa \left(T_{\mu\nu}-\frac{1}{2}g_{\mu\nu}T\right)+\Lambda g_{\mu\nu} $$ and then linearize them, we should get by moving to ...
Jon's user avatar
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Age of a dark energy dominated universe

In a flat universe that is dominated by dark energy (or cosmological constant), the Friedmann equation can be written as: $H^2 = (\frac{\dot a}{a})^2 = \frac{8\pi G\varepsilon_{\Lambda}}{3c^2}$ Where $...
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How do we account for the 'one way' drag of moving space?

As I understand it, the rotating space outside a Kerr black hole drags radially falling particles into circular motion. Similarly the river model posits that the inward flow of space ensures particles ...
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How to find critical density?

In Cosmology critical density is defined as the minimum density for a flat universe to keep expanding, by Friedmann Equation: ${\left({\frac {\dot {a}}{a}}\right)^{2}={\frac {8\pi G}{3}}\rho -{\frac {...
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How to understand critical density?

In Cosmology, critical density is given by setting $\Lambda = 0$ and $k = 0$, in other words, a universe without dark energy and zero curvature. According to my understanding and Wikipedia, this ...
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If space has a positive curvature, is the expansion of the universe caused by time, not "dark energy"? [closed]

Ok, I will assume that space has a positive curvature, where space is the "surface" of this sphere, and time is the radius from the center, so the universe is a 4D hypersphere. Under these ...
Rick Gennings's user avatar
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Do we really know the universal gravitational constant?

We've all heard $$F_g=\frac{gm_1m_2}{r^2}.$$ However, since I took physics, we've discovered "dark energy," which if I have any concept of the current thinking is caused by space being ...
Cristobol Polychronopolis's user avatar
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Different types of Dark energy and conservation of energy

According to this Sean Carroll article, and other threads in here, depending on your definition of energy, dark energy does not violate conservation of energy. My question is if this is true ...
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Why do people say that the $\Lambda$-CDM model has six independent parameters?

The Wikipedia article on the $\Lambda$-CDM model says that the model has six "independent parameters". It also says that the model has several "fixed" parameters and several "...
tparker's user avatar
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On vacuum energy in a de Sitter universe?

I have a couple of questions about de Sitter cosmological horizons. Initially I made a single post containing the two questions, but after some suggestions, I asked them in two separate posts. This ...
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The SI-unit of the cosmological constant (vacuum energy) is $\frac{1}{m^2}$. What does that have to do with Energy?

I just don't get how Energy is measured in $\frac{1}{m^2}$. Wasn't it measured in Joules? (source is https://en.wikipedia.org/wiki/Cosmological_constant#Equation)
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Model of Quintessential Inflation

I have a question about how the potential for an inflaton field is selected. It is clear that there are limitations associated with number of e-folds, scalar-to-tensor relation and scalar spectral ...
vorshchev's user avatar
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Cosmological implications of String theory compactification?

Is the process of compactification of hidden dimensions in string theory equivalent to an increasing dilaton field? Would one expect the compactification process to continue indefinitely? Could the ...
John Eastmond's user avatar
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Sign and physical meaning of the cosmological constant

I've heard that a cosmological constant can be used to model dark energy (e.g. $\Lambda$-CDM model), and that the constant $\Lambda$ should be positive. But my (quite small) understanding of dark ...
Chris's user avatar
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Solve Friedmann equation for non-zero curvature and non-zero cosmological constant

I tried to find an elegant way to solve (without approximating for low densities) $$\dot{R}^2=\frac{8 \pi G}{3 c^2} \rho R^2-k c^2+\frac{c^2 \Lambda}{3} R^2$$ for $k=\pm 1$ and $\Lambda \neq 0$ (one ...
Vincent ISOZ's user avatar
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Why are dark matter and dark energy favoured over changes to our physical models? [closed]

I am instinctively skeptical of the existence of "dark matter" and "dark energy". Together, they strike me as being analogous to luminiferous aether -- something that was invented ...
spraff's user avatar
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Negative $\Lambda$ FLRW spacetimes as infinite black holes?

Consider the Friedmann equation: $$H^2+\frac{k}{a(t)^2} = \frac{\Lambda}{3}+\frac{8 \pi}{3}\rho$$ and set the parameters for dust in either flat euclidean or open hyperbolic spatial slices with a ...
Michael C.'s user avatar
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Measurement of the Cosmological Constant

Is there some way to measure Lambda, the cosmological constant, independent of $H_o$, the Hubble constant and omega_lambda, the Dark Energy density? A standard equation for calculating Lambda, ...
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Why is there an infinite supply of energy in slow-roll inflation?

The physical model of inflation includes a metastable false vacuum, or a slow-roll field on a flat potential. In either case, I just realized how this is completely insane. With the exponential growth ...
Bababeluma's user avatar
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Will cosmic microwave background become invisible in the future?

If my understanding of CMB and Hubble's Law is correct, then CMB photons emitted from more than ~14.4 Glyr during Recombination Epoch would not reach us. The reason is this would correspond to Hubble'...
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What is the change in vision and measurement between curved space and flat space, especially for measuring cosmic background radiation?

In a curved space, the light bends as it travels and acts like it is going through a lens. In a (positively) curved universe, a small object appears larger. If we know the actual size of an object, ...
Saadeh Dayoub's user avatar
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Big Bang as stretching space time?

I am still new to researching the big bang so please be patient. I am having trouble envisioning the expansion. As I understand under current theory it is not to be thought of as a singularity ...
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Does energy exist on its own? [closed]

So to my understanding as a layman is that energy transfers from one material to another (I guess that's why there's potential and kinetic energy), for example photons to solar panels. Now my question ...
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Cosmological constant, dynamical friction and structure formation?

I would like to ask a question about an interesting article that I found (https://repositorio.unesp.br/server/api/core/bitstreams/b8a5a5b8-4b3b-4198-9f5d-bf69431db1ae/content) In the context of ...
vengaq's user avatar
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1 vote
2 answers
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Mass density and the cosmological constant?

So in flrw metric it's quite reasonable to take eigenvalue of the time-like component of the stress energy tensor and identify it with mass density. Now, if someone argues the cosmological constant ...
More Anonymous's user avatar
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Question about cosmological constant and radius of curvature of the universe

Dimensional analysis suggests that $\Lambda R^2 \sim O(1)$, where $\Lambda$ is the cosmological constant and $R$ is the radius of the universe. $\Lambda$ is measured to be around $10^{-52}$ m$^{-2}$, ...
Panopticon's user avatar
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1 answer
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Right hand side of Einstein field equation

Why can't the RHS of the Einstein field equations take a form like $T_{\mu \nu}$ plus some coefficient multiplied with $g_{\mu \nu} T$? It should also be covariantly conserved, I suppose? For example, ...
Yuan Liu's user avatar
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1 answer
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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_{...
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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 ...
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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 ...
Steven Vernau's user avatar
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1 answer
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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 ...
vengaq's user avatar
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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 ...
jboy's user avatar
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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.
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2 answers
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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 ...
Manosh T Manoharan's user avatar
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2 answers
304 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{...
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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 ...
Markoul11's user avatar
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2 votes
2 answers
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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 ...
Cham's user avatar
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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 ...
Muñoz Castro Yusef's user avatar
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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 ...
SPANDAN DASH's user avatar
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1 answer
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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 ...
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0 answers
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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, ...
Saadeh Dayoub's user avatar
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0 answers
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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 ...
Alucard's user avatar
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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 ...
AliceX's user avatar
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1 answer
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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 ...
user avatar
3 votes
1 answer
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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,...
More Anonymous's user avatar
5 votes
1 answer
738 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 ...
Jim Pivarski's user avatar
1 vote
1 answer
161 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 ...
Saber's user avatar
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2 votes
1 answer
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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 ...
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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 ...
Markoul11's user avatar
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2 votes
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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}+\...
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