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# Questions tagged [cosmological-constant]

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46 views

### Can universe still expand without energy and matter?

I heard dark energy is the intrinsic property of space and it cannot be particle because particle's density dilute when volume increase, I do not know how nothingness can have property and Einstein ...
519 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 ...
109 views

### Why is $\Lambda=0$ for a flat matter dominated universe?

I was looking over some of my cosmology notes and was considering the Einstein de-sitter model of a matter dominated universe. I know that in this case that k=0 and also furthermore that $\rho(t)$ is ...
70 views

### Why does dark energy make universe accelerate not slow down?

If mass=energy, then why doesn't dark energy not make the expansion slow down rather than accelerate seeing as gravity pulls masses together?
67 views

### Fiber manifold Ricci flat, physical meaning

In a warped-product spacetime, what a physical meaning we have for Ricci-flat Fiber? I'll explain.. it is well known that a Ricci-flat spacetime means that the cosmological constant need not vanish, ...
78 views

### Non-relativistic limit of the cosmological constant

Usually, when we apply the non-relativistic limit ($c \rightarrow \infty$) to relativistic equations, the cosmological constant $\Lambda \sim \mathrm{L}^{-2}$ is simply offhandedly neglected by ...
39 views

### Trying to make some sense of the cosmological constant

The question is simple: Does the naive reasoning below have some physical sense, or is it pure gibberish junk? (I use $c = 1$ and metric signature $\eta = (1, -1, -1, -1)$) I suppose that the ...
46 views

### What kind of average could give a Lorentz invariant energy-momentum tensor?

The electromagnetic (EM) radiation energy-momentum tensor is of the following shape, in the case of incoherent superposition of EM plane waves (I'm using $c = 1$ to simplify things, and metric ...
79 views

### Natural classification of fundamental constants of Nature

I was wondering about the fundamental constants of Nature since several years, and still pondering on them. Of course, I have read a lot of papers on them, but never found any satisfying ...
95 views

### Can we set cosmological constant equal to one?

People often say that the cosmological constant is too small. $\Lambda=10^{-120}$ in Planck units. Can we set $\Lambda=\hbar=c=1$ ? If so what would this give for $G$, the gravitational constant in ...
39 views

### How would we relate the cosmological constant to a dark energy distribution?

*Please excuse my lack of understanding of dark energy, the GR courses that I have taken so far haven't covered it How would we relate the cosmological constant to a dark energy density? Say we move ...
210 views

218 views

### Can a closed universe become open?

My feeling is that no a closed universe can't become open. Under normal evolution according to the Friedman equation the curvature would be more exagerated as time goes on (i.e. a a closed universe ...
148 views

### How did cosmologists calculate the small density of dark energy in our universe?

I've seen the number a few times (138 x10 to the power of -123) but i haven´t found how scientists calculated it. Max Tegmark mentions it in his research paper about multiverse types as representing ...
1k views

### Why is our physical Universe a de Sitter space?

Wikipedia says, When $n=4$ (3 space dimensions plus time), it is (the de Sitter space) a cosmological model for the physical universe; see de Sitter universe. It appears to me that the statement ...
71 views

### The universe is speeding up?

I just watched a show on spacetime. In the show they said that the universe's expansion is speeding up instead of slowing down. They said it had to do with dark energy. I was wondering if you could ...
142 views

### Is space in general relativity defined even when devoid of any energy?

General relativity is said to be background independent. Can we nevertheless think of a completely empty space (devoid of any energy) as if it is furnished with an elastic three-dimensional fabric, a ...
569 views

### Can String Theory really fail to contain a de Sitter vacua?

I was reading a post earlier from Peter Woit's Not Even Wrong blog and came across the following reference to the paper "What if string theory has no de Sitter vacua?" by Ulf H. Danielsson, Thomas Van ...
112 views

### What if Dark Matter is Majorana Fermion?

Few reasons to believe Dark Matter is Majorana fermion: https://arxiv.org/abs/1711.03877: second contra argument by Jordan and Pauli. "A non vanishing zero-point energy of elementary fields should ...
396 views

### How to calculate the vacuum expectation value of energy momentum tensor of a scalar field?

I have to prove that the vacuum expectation value of energy-momentum tensor of a scalar field (in flat spacetime) can be written as, $$\langle 0|T_{\mu\nu}|0\rangle=-\langle \rho\rangle\eta_{\mu\nu}.$$...
106 views

### Is the vacuum energy density proportional to the scale of the universe? [closed]

That is, does the vacuum energy density change with the scale $a$ of the universe according to $$\rho_Λ \sim a$$ ?
47 views

### Why are distances in cosmology larger with $\Lambda$?

I'm starting to study cosmology on these beautiful notes: http://www.damtp.cam.ac.uk/user/db275/Cosmology/Lectures.pdf . At page 16, when talking about distances in cosmology, the author says that ...
53 views

### Cosmological constant phase transition?

I recently watched at a talk by Cumrum Vafa in which he stated that the cosmological constant allows us to define a time-scale $T_\Lambda=1/\sqrt{E_\Lambda}$. The time scale of this time is about 10¹¹ ...
39 views

### Can a De Sitter universe have a detectable rotation?

In De Sitter relativity, the cosmological constant becomes a geometric term with the dimensions of radius, and the universe becomes a pseudo-sphere. Is it meaningful to speak of intrinsic rotation of ...
468 views

### Stress-Energy Tensor and the Vacuum

The Einstein field equations, $$R_{\mu \nu} + \left ( \Lambda - \frac{1}{2}R\right )g_{\mu \nu} = \frac{8\pi G}{c^4} T_{\mu \nu}$$ relates the curvature of spacetime and density and flux of energy ...
150 views

### Inflation and dark energy have constant energy density - energy is created out of nothing without any source or mechanism?

I can understand that a photon in an expanding universe can be redshifted and lose its energy by its wavelength being stretched from space expansion. But in the case of inflation and dark energy, it ...
208 views

### Cosmological constant problem and dark matter theory by Henke

Christian Henke has recently proposed one approach for the solution of the cosmological constant problem and of the dark matter dynamics: Quantum vacuum energy in general relativity Abstract: The ...
76 views

### How is expansion of universe seen locally? [duplicate]

Traditionally when deriving Friedmann–Lemaitre–Robertson–Walker metric, homogeneity and isotropy assumption is made. This assumption, however, holds only for large scales. To take into account some ...