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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What mechanism would choose the smallest cosmological constant from string vacua? [duplicate]

According to Wikipedia "the problem of finding [a string vacuum] with a sufficiently small cosmological constant is NP complete". This got me wondering if our Universe might be the one ...
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How you calculate the age of the observable Universe if the acceleration expansion is not constant?

What makes us believe that the Cosmological constant was the same in the past? And if there is no way to prove this then could the age of our Universe be different from the current calculated value ...
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Why is the cosmological constant is taken to be a free parameter if its experimental value is $\sim 10^{-52}$?

I have been studying a paper on neutron stars in Einstein-$\Lambda$ gravity. In this paper, the cosmological constant is considered a free parameter. Now, isn't the cosmological constant already known ...
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The unit of the cosmological constant

In natural units, it’s known that the unit of the cosmological constant is $\text{eV}^2$. I don‘t get why the paper arXiv: 2201.09016, p. 1, it is said the value of $ \Lambda \sim \text{meV}^4$, this ...
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Is this right that the fate of space expansion depends on matter density inside the universe?

Is it right think that a right amount of matter density inside the universe could eventually stop the expansion of the universe or the expansion of space is something intrinsic only to space so the ...
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How does the strength of dark energy compare to the strength of the other forces?

I have read this question: http://hyperphysics.phy-astr.gsu.edu/hbase/Forces/funfor.html So , in a nutshell, it is the fitting of data with a specific standard model that organizes the particle ...
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Cosmological constant divergence [closed]

The cosmological constant is measured to be of the order of $10^{120} $ smaller than the value which has been calculated from quantum mechanics. As far as I know, usually this divergence is attributed ...
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Cosmology from within a black hole

Suppose an astronaut is travelling "into" a black hole and has already passed the Schwarzschild boundary (as described in this video). What will the universe look like to this astronaut, ...
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Could dark matter be just a gravitational effect of dark energy?

I'm wondering if we just looking at the two sides of the same coin and if there is actually a correlation of DM with DE? Is it possible that DM just to be a gravitational effect (or an effect that ...
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In an expanding universe, can two people communicating to each other about their cosmological horizons get around their horizon limit?

I want to pose a preamble question that I will answer first to build up to the main scenario. Then I will pose the main question. The main question concerns the special case of an expanding universe ...
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Schwarzschild-deSitter horizon singularity

The Schwarzschild-deSitter spacetime in Euclidean signature is given by: $$ ds_{E}^{2}=\left(1-\frac{2M}{r}-\frac{H^{2}r^{2}}{3}\right)d\tau^{2}+\frac{dr^{2}}{\left(1-\frac{2M}{r}-\frac{H^{2}r^{2}}{3}\...
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Based on structure formation and the lifetime of the universe why is there an upper bound on the cosmological constant?

I understand that significantly greater values than the cosmological constant would result in difficulty for the formation of large gravitationally bound structures within the lifetime of the universe....
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About a hypothetical universe

Imagine a universe dominated by matter, but it is balanced with a cosmological constant $\Lambda=4\pi G\rho$ so the universe is static ($H=0$). However, what would happen if some of that matter turns ...
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Is it OK to do this manipulation at the partition function level? (auxiliary fields in quadratic gravity)

Background I am working with the following action in the Euclidean signature ($C^2$ is the Weyl quadratic term): \begin{equation} S_B = -\frac{1}{2\kappa^2}\int d^4x\sqrt{g}\left(2\Lambda_C+\zeta R-\...
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Why is the current cosmological constant insufficient to solve the flatness problem?

The flatness problem can be very succinctly summarized by the fact that the density parameter $\Omega(t)$ has an unstable equilibrium point at $\Omega = 1$ (which corresponds to a Euclidean universe). ...
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Can dark energy expand the distance between the earth and the sun?

I remember that the expansion is 0. Is it exactly 0 or just really close?
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Is it a fact that vacuum energy exists?

I have always read that vacuum energy and zero point energy are established facts of physics supported by various observations of their effects both indirectly and even directly. But I have also read ...
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Validity of Friedmann's equation

Recently, a friend gives me the Friedmann's equations under the following form: \begin{gathered} \left(\frac{\dot{a}}{a}\right)^{2}=\frac{8 \pi G}{3 c^{4}} \rho+\frac{\Lambda}{3}-\frac{k}{3 a^{2}}\...
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Did Einstein really invent the cosmological constant to make the universe static in his 1917 paper?

The popular account of Einstein inventing the cosmological constant goes like this: Einstein finds that the Einstein Field Equations predict an expanding universe Unable to accept this, Einstein adds ...
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Relationship between expanding space and dark energy [duplicate]

The excerpt below has been taken from a pop-science article. Dark energy is thought to be different, though. Rather than being a type of particle, it appears to behave as though it were a type of ...
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Does dark energy redshift over time?

In the expanding universe, light is subject to redshift. Does redshift also affect dark energy - and why?
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Does the Schrödinger equation take vacuum energy into account?

As I understand it (and excuse me if I get it wrong or partially wrong), the Schrödinger equation is an energy equation that states that the energy of a quantum system stays constant in time. So how ...
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Can I calculate the stress-energy tensor for the following problem?

In two spacetime dimensions the Einstein tensor is identically zero. Therefore if we consider the EFE with a non-zero cosmological constant and a stress-energy tensor as: $$\Lambda g_{\mu\nu} =\alpha ...
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Which universe has more entropy?

Lets say I have $2$ universes with fluid stress energy tensors: $$T_1^{\mu \nu} = (\rho + p/c^2) u^\mu u^\nu + p g^{ \mu \nu} + \Lambda_1 g^{ \mu \nu}$$ $$T_2^{\mu \nu} = (\rho + p/c^2) u^\mu u^\nu + ...
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Why do some scientists believe that the zero point radiation of the vacuum is incredibly powerful?

I've been doing some research and i read about zero point energy. I've heard that a couple cubic cm of it can boil the earth's oceans. how does this work if the energy is only 2.7 kelvin? and what are ...
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Absence of matter stretches the fabric of space?

If matter attracts matter, because it curves the space, could it be that the absence of matter stretches the space, and that's why the universe expansion is accelerating? I mean that could be ...
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Calculating galaxy power spectrum

I have been trying to calculate the theoretical value of the Galaxy Angular Power Spectrum($C_l$), and I have referred to a number of papers, but the problem that I have been facing is that there is ...
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Why is AdS spacetime like a "saddle"?

When the shape of the universe is discussed, the three cases are flat, closed and open. Where AdS spacetime with a negative cosmological constant describes the open spacetime, as in the middle in the ...
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What is the relationship b/w mass’s effect on the curvature of space vs the expansion of space?

As is well known, General relativity explains that mass and energy bend the curvature of spacetime. Mass energy of different amounts lead to different space time curvatures. As is also well known, the ...
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Would Birkhoff's Theorem also apply for a field with negative energy density?

Birkhoff's Theorem says that any spherically symmetric solution to the field equations must be the Schwarzschild metric. I'm wondering whether that could be generalized to a field with negative energy ...
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Why would it break Lorentz invariance if $\rho_{\text{vac}} $was not equal to $-p_{\text{vac}} $?

Using $\Lambda$ in the field equations, one can derive that then $p_{\text{vac}} =-\rho_{\text{vac}} $. The energy density of the vacuum is the same (with opposite sign) as the pressure of the vacuum. ...
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Two cosmological Constants?

The cosmological constant $\Lambda$ can be written as part of the T-Tensor. It can then be considered as vacuum energy ($\rho_{vac}$) and vacuum pressure($p_{vac}$). $\rho_{vac}$ and $p_{vac}$ are the ...
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Does vacuum spacetime have an inherent curvature?

I am a complete novice in physics beyond the high school level, so please excuse anything wrong in my question. So I have recently read that according to General Relativity, the presence of mass in ...
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Did the universe need the presence of matter and radiation to start expanding?

I have read this question: Hence it is not possible that photons generated by stars is contributing to dark energy. Could photons generated from the many trillions of stars be some how contributing ...
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Would a 1022-keV vacuum contain real electron-positron pairs?

The cosmological vacuum energy scale is measured to be about $10^{-3}$ eV (see David Tong Quantum Field Theory Lectures, ch. 0, p. 5) As I understand it this implies that the vacuum contains zero-...
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Would the cosmological vacuum heat a hollow box?

The energy scale of the cosmological vacuum is about $10^{-3}\mbox{eV}\approx10\mbox{K}$. Imagine cooling an insulated hollow metal box with a vacuum inside it down to near $0\mbox{K}$ and then ...
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Dilaton field causes universe expansion?

In string theory low-energy $n$-dimensional gravity is described by an action of the following form: $$S^{(n)}=\frac{1}{2\kappa^{(n)}}\int d^nx\sqrt{-G}e^{-2\Phi}\Big(\mathcal{R}+4\partial_\mu\Phi\...
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Writing the metric of 4D de Sitter space as a 5D metric

It is often said that the 4D de Sitter metric may be obtained as the induced metric on a hyperboloid embedded in 5D Minkwoski space. The hyperboloid is $$ -x_0^2+x_1^2+x^2_2+x_3^3+x^2_4=l^2~~. $$ I ...
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Why does $10^{-31}$K change the orbits of the stars, but 2.7K does not?

Many people discussing the rotation curves of the stars in galaxies explain that the rotation curves are influenced by a cosmological acceleration of about $1.2 \cdot 10^{-10}\,\rm m/s^2$, and that ...
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Is it possible that dark energy could be non-uniformly distributed?

Is it even possible that dark energy could be non-uniformly distributed? If it were the case at some points where creation is faster would some objects like for example stars move apart with a rate ...
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Would the distance to the cosmological horizon change if the value of the cosmological constant changed?

I intuitively understand that the distance from the Earth to the cosmological horizon (separating events that can reach us from events that never reach us) depends on the value of the cosmological ...
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What does adding a scale in the action means?

I was reading the paper Analytic topological hairy dyonic black holes and thermodynamics, where in page two in the second paragraph, the authors write: "One way of ensuring regular scalar field ...
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$3$-dependent self-similar solutions for the universe using derivation of Friedmann equations

So I began this with a Newtonian derivation of the Friedmann equations. Now I'm supposed to figure out the following: Considering solutions that are self-similar, i.e. the same "shape" ...
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1 vote
1 answer
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What is the behaviour of massive particles traveling between tethered galaxies in the FLWR metric?

I was reading the following papers, arXiv:astro-ph/0104349 and arXiv:astro-ph/0511709. Both papers investigate the situation where two galaxies are held together by some sort of tether, such that the ...
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2 votes
3 answers
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How can the cosmological constant be $1/R^2$ and still be constant in time?

The cosmological constant $\Lambda$ is roughly the inverse square of the size $R$ of the observable universe, or horizon radius (with proper constants to get the right units). $\Lambda$ has a solid ...
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How should we deal with interactions not from a “fundamental force”? [closed]

Question Should the cosmological constant and/or vacuum energy be listed as one of the fundamental interactions? If not, how can we have actual energy and forces that are not assignable to one of the ...
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Could 'dark' energy just be ordinary photons?

I had this idea a while ago that dark energy might just be ordinary photons 'building up' in the recesses between galaxy clusters and giving rise to the expansion of the universe. I know that the ...
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Could Dark Matter imply the existence of Dark energy? [closed]

This is admittedly a simple example, but it seems to check out. Consider the standard metric for the Schwarzschild solution in coordinates $(t, r,\theta,\phi)$: $$ g_{oo} = U, \ g_{11} = V, \ g_{22} = ...
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Why are the radius of the observable universe and radius of curvature of dark energy almost the same?

If you take the Einstein equation, $R_{\mu\nu} - \frac12 Rg_{\mu\nu} = \frac{8\pi G}{c^4}T_{\mu\nu}$ and plug in the estimated vacuum energy of $10^{-9} J/m^3$ for $T_{\mu\mu}$, you get a spatial ...
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Anti de Sitter & de Sitter Spacetime [duplicate]

Can anyone please explain what are the Anti de Sitter and de Sitter spacetime and what is special about them? I am learning general relativity and I stumbled upon them a few times, even on the subject ...
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