Questions tagged [cosmological-constant]

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1answer
2k views

Why did Einstein introduce expansion in his equation and later on it was patched?

I read that in developing GR, Einstein's original equation indicated that the universe is expanding and later he quickly dismissed it by adding the cosmological constant. I kept wondering, why did he ...
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1answer
58 views

What does the cosmological constant do? [duplicate]

I think just about anyone who has studied Einstein or relativity has heard of the cosmological constant. He added it so that his equation would return an universe that is static. Of course, the ...
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2answers
104 views

What is the difference between the quantum fluctuation, the zero point energy and the cosmological constant?

I have difficulty to understand the real difference between those three concepts of the energy of the vacuum it's self.( Quantum fluctuation, the zero point energy and the cosmological constant.) I ...
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1answer
75 views

What is the largest gravitationally bound structure in the universe?

I understand the galaxy superclusters are not bound due to dark energy. I wonder what matter scale will remain gravitationally bound - galaxy clusters, galaxies, stars - if anything at all, as dark ...
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22 views

Can cosmological parameters be quoted more precisely at other epochs?

Inspired by Value of density parameters in CMB time it seems to me that when cosmological parameters are quoted (e.g. from the CMB or type Ia supernovae), they are almost exclusively quoted in terms ...
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1answer
98 views

Entropy of de-Sitter spacetime and the $10^{120}$ vacuum discrepency

While doing some lazy calculations, I came across a curiosity that I'm unable to interpret. It is well known that the cosmological constant $\Lambda \sim 10^{-52}~\mathrm{m^{-2}}$ is usually ...
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1answer
53 views

Vacuum energy and cosmic graviton background

What is the best way to show that vacuum energy (the cosmological constant) cannot be the same as a cosmic graviton background (or cosmic gravitational radiation background)?
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1answer
146 views

What conceivable connection is there between the cosmological constant and radius of the Universe?

You probably noticed that the radius of the (observable) Universe in Planck lengths $R$ (about $10^{60}$) and the cosmological constant $\Lambda$ (about $10^{-120}$) in natural units obey ...
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2answers
173 views

Is the acceleration of the expansion of the universe caused by expansion of spacetime itself?

When considering the accelerating expansion of the universe, it is often stated that dark energy is required to cause acceleration of expansion in order to overcome the pull of gravity. However, it ...
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0answers
17 views

realistic string cosmology and cosmological constant

Apparently one can recover the Friedman Equations from String Cosmology where the critical dimensions is lowered (from 26) to four. If this is the case, is the bosonic partition function (~ ...
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1answer
155 views

Is it possible to directly test whether of not the vacuum gravitates?

According to GR, all sources of stress-energy (e.g. everything on the $T_{\mu\nu}$ side of the EFE) should gravitate (e.g. affect the curvature/$G_{\mu\nu}$ side of the EFE). We observe the expansion ...
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25 views

large extra dimensions, ADD scenarios and current bounds

What is the current status of ADD and more generally large extra dimension models at the moment? Is there any prospects of natural phenomenology coming from it now or has it died like technicolor, etc....
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1answer
95 views

Finding de-Sitter Schwarzschild Metric

Given the metric in Schwarzschild coordinates $$d s^{2}=-e^{2 \Phi(r)} d t^{2}+e^{2 \Lambda(r)} d r^{2}+r^{2} d \Omega^{2}$$ and a vacuum Einstein equation with cosmological constant given by: $$G_{...
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Does this paper falsify the vacuum energy? [duplicate]

If Dark Energy is falsified by this paper, https://arxiv.org/abs/1808.04597, does that mean the vacuum energy is also falsified?
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1answer
130 views

Does the cosmological constant solve the flatness of the Universe with 2 independent methods?

First. The universe is flat and not negativity curved because whatever dark energy is made from represented by the cosmological constant adds to the side of the density in the first Friedman equation: ...
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1answer
133 views

Is cosmological constant some kind of field that permeates all of space?

One simplest candidate for dark energy is a cosmological constant. Is cosmological constant some kind of field that permeates all of space, or is it just some kind of energy stored in space?
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2answers
212 views

The cosmological constant and the precession of Mercury

In the beginning of the last century, the Nobel physics subcommittee – made up of experimentalists detached from the dramatic developments of theoretical physics on the continent – was surprized both ...
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101 views

Is the cosmological constant problem real?

The cosmological constant problem assumes that the cosmological constant (determined experimentally) can be identified with the vacuum energy density. Theroretical arguments from quantum gravity ...
4
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1answer
217 views

Shouldn't the infinite sea of electrons contribute to gravity?

According to my understanding of the dirac equation, there's an infinite sea of electrons occupying all negative energy states which prevents an electron from dropping to lower and lower energy states ...
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51 views

Why is de Sitter spacetime a better model of our universe than brane world models?

Why is it assumed that we live in a de Sitter space-time? Besides the de Sitter Lambda Cold Dark Matter model, there are Anti de Sitter brane world models, which also generates Friedmann equations ...
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0answers
43 views

Holographic AdS/CFT intepretation of Cosmological Constant

I'm trying to understand how the value of AdS cosmological constant (or, equivalently, of AdS radius) affects the boundary CFT in AdS/CFT correspondence. I'd be glad of discovering something about the ...
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36 views

Can you cancel the Large Vacuum Energy with a weird Scalar Field?

Something like the Chameleon field which gives a density dependent potential which in turn contributes to the vacuum energy. Is there a room to wiggle to modify it so all possible vacuum energies will ...
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1answer
51 views

If universe was instead cosmological blueshifted, would we still notice dark energy?

Imagine instead of us seeing more distant galaxy turning redder, they now becomes more blue at a similar rate. This time round would we be able to notice those mythical dark energy? I suppose missing ...
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21 views

Fine-tuning of the cosmological constant (reference request)

It has been claimed in various places on the internet and in books by non-physicists (i.e. by unqualified people) that if the cosmological constant $\Lambda$ had a value different by so much as $10^{-...
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Negative temperature of the de-Sitter horizon?

I'm considering the $4D$ de-Sitter spacetime, in static coordinates (I'm using $c = 1$ and $k_{\text{B}} = 1$): \begin{equation}\tag{1} ds^2 = (1 - \frac{\Lambda}{3} \, r^2) \, dt^2 - \frac{1}{1 - \...
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4answers
210 views

What would happen to de Sitter universe if the cosmological constant disappears?

De sitter universe is dominated by a cosmological constant (devoid of matter and radiation), corresponding to dark energy in the far future or the inflaton field in the early universe, leading to an ...
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1answer
80 views

What is the Komar mass of the de-Sitter spacetime?

The Komar mass of some spacetime is defined as an integral (volume or surface, depending on its formulation): https://en.wikipedia.org/wiki/Komar_mass The de-Sitter metric in static coordinates is ($\...
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1answer
61 views

Radial null geodesics in Schwarzschild de Sitter space

I am currently studying the geodesics of different type of spacetimes and I'm not sure if I'm doing it in the correct way for Schwarzschild de Sitter space (SdS). The metric in SdS is given by: $$ ds^...
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1answer
171 views

Does $\Lambda$CDM include inflation?

$\Lambda$CDM obviously includes dark energy (the $\Lambda$) as well as cold dark matter (CDM). Does it also include cosmic inflation? I've not seen a clear answer to this. Wikipedia's article on ...
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1answer
47 views

Is there cosmic background radiation in de Sitter space?

This is a simple question of understanding. Would a de Sitter universe show cosmic background radiation? (After all, it is often explained said that our universe is similar to a de Sitter universe.) ...
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3answers
675 views

Is zero-point energy real?

In the context of canonical quantization, the ground state/zero-point energy of a harmonic oscillator is $$ E_0 = \frac{1}{2}\hbar \omega. $$ The vacuum is alleged to be permeated with this zero-point ...
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4answers
549 views

What does the 'cosmological constant' represent?

Newtons theory of gravity involves a gravitational constant $G$, however one does not refer to it directly, we speak instead of gravity or the force of gravity. Now Einsteins introduced a ...
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1answer
59 views

What do the terms attractive and repulsive gravity mean in Einstein's GR?

What does the jargon repulsive gravity mean in Einstein's GR or even attractive gravity in the same framework? The notions of attractive and/or repulsive only makes sense, or at least we are ...
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1answer
63 views

Strange anomaly in the calculation of the cosmological constant

I was trying to calculate the cosmological constant with two different methods proposed on the internet, that are apparently equivalent but they give different results and different dimensional ...
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1answer
531 views

Entropy of the cosmological constant and the laws of thermodynamics?

Convention The convention being used is: $ A_{C} = $ The classical variable Premise Consider the following toy-model universe: A universe with a positive cosmological constant. Basic ...
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21 views

Cosmological Constant: negative pressure [duplicate]

I am a little confused about the statement that the Cosmological Constant in General Relativity corresponds to negative pressure. I thought that the Cosmological Constant is responsible for the ...
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1answer
105 views

Why did dark energy play a subdominant role in the radiation and matter dominated era?

After inflation, the Universe passed through radiation dominated (RD) and matter dominated (MD) era during both of which the evolution of the scale factor (or the Hubble parameter) was decreasing with ...
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1answer
236 views

Fine Tuning of the Universe

I'm an A level student looking into the fine tuning of various constants. Physicists explain the extensive effects that would happen if these constants were to be changed/different and hence, how this ...
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1answer
85 views

“Cosmological constant problem” and dark energy

Simply stated: is the "cosmological constant problem" (the discrepancy of about 120 orders of magnitude between measured values of vacuum energy and the ones predicted by Quantum Field Theory) in any ...
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0answers
36 views

Quintessential models for dark energy

Following Sean Carroll here There are good reasons to consider dynamical dark energy as an alternative to an honest cosmological constant. First, a dynamical energy density can be evolving slowly ...
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1answer
174 views

Energy/mass of Quantum Vacuum

So far as we have measured the volume of the universe, has anyone calculated the virtual energy/mass of the Quantum Vacuum? If so, what? Or if not, a local volume such as 1 sq. meter? This relates to ...
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1answer
95 views

Is there a cosmological constant $\Lambda$ in 2D?

It is well known that the Einstein tensor is trivially 0 in any two dimensions spacetime: \begin{equation}\tag{1} G_{\mu \nu}^{(2)} \equiv 0. \end{equation} Thus, it is not possible to formulate the ...
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1answer
156 views

Minkowski space vs De Sitter Space

Can you explain to a layman the differences between the former two?
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3answers
700 views

Is the “cosmological constant tension” the prime reason that we believe the expansion of the universe is accelerating?

Background: For a few years now there is significant difference in the calculation of the cosmological constant between standard candles methods and CMB methods. CMB measurement comes from a very ...
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0answers
62 views

Fine tuning of the cosmological and gravitational constants [closed]

Consider the gravitational constant $G$. According to philosopher Robin Collins, cosmologists have been able to determine a region $W_r\subseteq\mathbb{R}$ for which the universe would have permitted ...
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23 views

Intergalactic medium and cosmic expansion

Presumably, the intergalactic medium (IGM) should get less dense as the universe expands. Also presumably, There should be a Hubble redshift to absorption lines due to the IGM. Could this provide ...
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0answers
64 views

How come the universe is considered flat if zero point energy is infinite?

If quantum field theory calculates that the vacuum energy is infinite and Einstein's theory of gravity implies this energy should produce a curvature of space-time then why shouldn't the universe be ...
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1answer
82 views

Maxwell equations in curved spacetime with cosmological constant

I am aware of Maxwell Equations in Curved Spacetime. But how do these equations change if the cosmological constant is not assumed to vanish?
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6answers
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Why isn't an infinite, flat, nonexpanding universe filled with a uniform matter distribution a solution to Einstein's equation?

In Newtonian gravity, an infinite volume filled with a uniform distribution of mass would be in perfect equilibrium. At every point, the gravitational forces contributed by masses in one direction ...
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1answer
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What's the difference between “dark energy” and “vacuum energy”?

Let's see if I understood well. "Dark energy" is a term that encapsulates everything that may be accelerating the expansion of Universe, and "vacuum energy" is a kind of energy that permeates the ...

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