Questions tagged [de-sitter-spacetime]

The tag has no usage guidance.

Filter by
Sorted by
Tagged with
2
votes
0answers
36 views

De Sitter horizon area increase

Black holes increase area when any object falls past the horizon. Note: We define "when" as when the hair from the object falling in becomes undetectable for distant observers. It would also ...
1
vote
0answers
41 views

Is there a smooth, spherically symmetric, static, asymptotically de Sitter spacetime of constant scalar curvature?

...other than de Sitter space itself? Two clarifications: I am not talking about solutions of Einstein's equations, just spacetimes. So, general Lorentzian manifolds. I am not counting, for example,...
0
votes
1answer
42 views

The contravariant derivative of a substitution for the de Sitter metric

Consider the de Sitter metric: $$ds^2 = (1-\frac{r^2}{a^2})dt^2 -(1-\frac{r^2}{a^2})^{-1}dr^2-r^2d\Omega^2$$ I know that we rewrite the metric as $(u,r,\theta \phi)$ using the substitution $$u = t-...
0
votes
2answers
130 views

Timelike geodesics of 2-dimensional de Sitter spacetime

The de Sitter spacetime in two dimensions ($\text{dS}_2$) can be spanned by two coordinates : $\tau$ and $\phi$ (can be viewed as a cylinder). The metric is then defined as follows : $$ds^2=-d\tau^2+\...
2
votes
1answer
66 views

Construction of Carter-Penrose diagram for DeSitter spacetime

The DeSitter spacetime line element in global coordinates is given by $$ds^2 = -dt^2 + \frac{1}{H^2}\cosh^2(Ht)\left(d\chi^2 + \sin^2(\chi)(d\theta^2 + \sin^2(\theta)d\phi^2 \right).$$ The ranges of ...
2
votes
0answers
53 views

Bose-Einstein statistics in de Sitter spacetime

The metric in de Sitter spacetime with $(+,-,-,-)$ as metric signature is, in cartesian coordinates: \begin{equation} ds^2=dt^2-a^2(t)(dx^2+dy^2+dz^2). \end{equation} Where $a(t)=e^{Ht}$. How do I ...
0
votes
0answers
30 views

Question regarding different mode functions in FRW spacetime

I am currently reading Mukhanov's and Winitzki's book with title: "Introduction to Quantum Fields and Classical Backgrounds". At chapter 6, they argue that in a FRW (Freedman - Robertson - ...
0
votes
0answers
24 views

What happens to the information content of the universe in the deSitter phase?

What happens to the information content of the universe when the accelerated expansion enters the empty deSitter phase in the distant future?
3
votes
2answers
280 views

de Sitter Spacetime: Static patch vs Global coordinates

Two well-known coordinate charts on the dS spacetime are the global coordinates and the static patch coordinates. In the global coordinates, the D-dimensional dS metric takes the following form $$ ds^...
1
vote
0answers
45 views

How to check if some metric has a particular type of geodesics?

For instance, we want to know if cylindrically symmetric de Sitter-type spacetime has an axial geodesic. This is the metric I am interested in $$ds^2= \cos^{\frac{4}{3}}\left(\frac{\sqrt{3 \Lambda}}{2}...
2
votes
1answer
185 views

Interpretation of horizon in de Sitter

Given the de Sitter metric for spacetime $$ds^2 = \left( 1 - \frac{\Lambda}{3}r^2\right) dt^2 - \frac{1}{\left( 1 - \frac{\Lambda}{3}r^2 \right)}dr^2 - r^2d\Omega^2 $$ we understand this is a solution ...
3
votes
0answers
119 views

How does $1/r$ gravity change in de Sitter space?

Classical $1/r$ gravity arises from general relativity when curvature is neglected and speeds are small compared to the speed of light. In de Sitter space with a positive cosmological constant $\...
3
votes
0answers
80 views

Understanding Verlinde: How to get from emergent gravity to MOND

Verlinde ( https://arxiv.org/abs/1611.02269 ) tries to deduce MOND from emergent gravity. Can you help? Emergent or entropic gravity goes back to Jacobson. He starts with the entropy-area connection $...
6
votes
2answers
145 views

de-Sitter space as near-horizon limit of Black Holes

We know that we can obtain $AdS_{2}$ x $S_{2}$ spacetime as the near-horizon geometry of an extremal/ near extremal RN (or Kerr) Black Hole in asymptotically flat spacetime. It is also known that we ...
0
votes
1answer
111 views

Is de Sitter space homogeneous?

Since Minkowski and anti de Sitter are homogeneous Lorentzian manifolds, it is natural to ask if de Sitter is too, but nobody ever discusses this. In Riemannian geometry a globally symmetric complete ...
1
vote
0answers
19 views

Jacobi Identity in de Sitter Superalgebra

In the book "Supergravity" (by D. Freedman and A. Van Proeyen) they talk about why $\mathcal{N}=1$ de-sitter superalgebra is impossible to construct (Section 12.6.1). Basically de-Sitter algebra is a ...
5
votes
0answers
356 views

Casimir operators of de Sitter space

De-Sitter space can be thought of as a 4 dimensional hyperboloid embedded in 5D Minkowski space. Hence, the symmetry group of dS is $SO(1,4)$ whose generators are, $J_{AB}=i\left(X_A\frac{\partial}{\...
1
vote
1answer
158 views

de Sitter vacua in String Theory

I don't quite understand what goes wrong with the de Sitter vacua in string theory. Firstly, how are the vacua calculated (I'm given to understand there is no standard method, so what are the efforts ...
2
votes
1answer
275 views

Does de Sitter space have a preferred frame?

Consider the flat, expanding coordinates for de Sitter space: $$ds^2=-dt^2+e^{2Ht}d\vec{x}^2\quad .$$ This is clearly not invariant under the ordinary Lorentz transformations. Does this mean that if I ...
0
votes
1answer
114 views

Massive particles in de Sitter space

Can massive particles in de Sitter space move faster than light? For the radial coordinate (in static coordinates) I have got the hyperbolic expression $$r(\tau)\propto \sinh\left(\sqrt{\frac{\...
3
votes
0answers
121 views

Supersymmetry in de Sitter space

Is it possible to construct SUSY theories in de Sitter space? I know statement: dS superalgebras cannot be constructed unless one constructs actions with matter coupled with the wrong signs for ...
6
votes
1answer
198 views

Newton's law of gravitation in de Sitter space

Given two masses $M$ and $m$ (with $M\gg m$) in a de Sitter background with cosmological constant $\Lambda>0$ and positive spatial curvature ($k=+1$). What is the corresponding (semiclassical "...
1
vote
1answer
92 views

String Landscape, De Sitter vacua and Broken Supersymmetry

If we assume that the swampland conjectures, etc. regarding de sitter vacuas existence in the string / F-theory landscape turn out to be incorrect (and therefore we can assume the problem is well-...
0
votes
1answer
144 views

How to pick what coordinates transformations to apply in general relativity?

I've been challenged by coordinate transformations lately, as most of you know during solving any problem in GR we have to go through lots of transformations, my question is how we decide the best ...
0
votes
0answers
75 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 ...
1
vote
0answers
53 views

AdS/CFT phenomenology and realistic FRW model building

Are there any examples of realistic holography (likely as a de Sitter type Universe: as it approximates FRW / is an FRW solution without baryonic and dark matter). I don’t see why one wouldn’t be ...
2
votes
1answer
182 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 ($\...
5
votes
1answer
273 views

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 - \...
4
votes
2answers
231 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 ...
1
vote
0answers
45 views

dS/CFT in a positive curvature universe

Since Maldacena ground breaking theoretical discovery, have there been any succesfull efforts to try to transpose the AdS/CFT duality to our universe (not an AdS)?
2
votes
1answer
127 views

Symmetry v.s. isometry of Minkowski and AdS or dS spacetime

We know some nice spacetime have a lot of symmetries. It is said that Minkowski spacetime has $$ISO(d-1,1)/SO(d-1,1),$$ de Sitter spacetime has $$SO(d,1)/SO(d-1,1)$$ and anti-de Sitter spacetime ...
0
votes
1answer
32 views

In de Sitter space, does the cosmic horizon change its shape for fast-moving observer?

If an observer moves at a speed close to the speed of light, will the horizon deviate from spherical shape? If no, will it be the same horizon as for stationary observer (at the same position)?
1
vote
0answers
49 views

Given in de Sitter space time is frozen on the horizon, can we say that in anti-de Sitter space time goes infinitely fast at the space boundary?

Particularly, in de Sitter space everything on the cosmic event horizon is redshifted, while in anti-de Sitter space everything on the horizon is blueshifted.
2
votes
1answer
437 views

Minkowski space vs De Sitter Space

Can you explain to a layman the differences between the former two?
0
votes
1answer
97 views

Does an observer inside a black hole experience the de Sitter metric?

My question has emerged, because of the following similarities between the metric an observer experiences in the Schwartzschild space being under the Schwartzschild radius and an observer in the de ...
0
votes
0answers
94 views

How accurate is the De Sitter solution of the Einstein field equations of general relativity?

The De sitter solution models the universe as spatially flat, neglecting ordinary matter, such that it is dominated by the cosmological constant. The cosmological constant notion arguably suggests the ...
2
votes
0answers
34 views

How is deSitter group tranformations different from poincare group transformations

In QFT, we have studies Poincare group of massive and massless particles. Is the deSitter group also useful to study such things? What exactly is the main role of this group in QFT? I just know the ...
2
votes
4answers
279 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 ...
0
votes
0answers
33 views

2D deSitter conserved charges

For $1+1$-dimensional dS spacetime, the metric takes the form (in comoving coordinates) $$\mathrm{d}s^2=\left(\mathrm{d}x^0\right)^2-e^{2Hx^0}\left(\mathrm{d}x^1\right)^2.$$ I want to find the ...
0
votes
0answers
69 views

deSitter spacetime metric and curvature

I have to compute the metric of an hyperboloid given by $-(X^0)^2+(X^1)^2+(X^2)^2+(X^3)^2=H^{-2}$ in 5D Minkowski spacetime using the following coordinates: $$X^0=H^{-1}\sinh(Ht)\sqrt{1-H^2r^2}$$ $$X^...
0
votes
1answer
69 views

$dS^d$ and $AdS^d$ are conformally equivalent

I have seen in the book by Zee (Einstein Gravity in a Nutshell) the following metric for $dS^4$: $ds^2 = \frac{1}{\cos^2 \tau} \big( - d\tau^2 + d\psi^2 + \sin^2 \psi \, d\Omega_2^2 \big) $, (Eq. IX....
2
votes
1answer
84 views

Why $dS^d \cong SO(d,1)/SO(d-1,1)$?

I have found a similar question, but there they give a seemingly rigorous proof, and what I am looking for is just an intuition. I understand that $S^2 \cong SO(3)/SO(2)$: for every point in $S^2$ ...
3
votes
1answer
784 views

Metric for 2D de Sitter?

What is the correct metric to use for two dimensional de Sitter? If one starts with the following metric, which looks similar to de Sitter in 4 dimensions: $$ds^2 = -dt^2 + e^{2H t} dx^2,$$ one can ...
1
vote
1answer
111 views

Lorentz transformations in non-Euclidean geometries

I have an assessment/investigation coming up in my math class and I plan to investigate Lorentz transformations in geometries other than Euclidean such as spherical or hyperbolic. For spherical/polar, ...
3
votes
0answers
101 views

Strings 2018 takeaways [closed]

What are the main takeaways from the Strings 2018 conference? What are the main announcements, discoveries or directions emerging from this event? To my knowledge, one is the result by Vafa and ...
2
votes
0answers
142 views

If the Schwarzschild radius of the universe is bigger than the universe, how come the universe didn't collapse into a black hole? [duplicate]

According to this answer, the Schwarzschild radius of the universe is about 3 times the radius of the universe. According to the Newtonian theory of gravity, inside any sphere of a given density, the ...
3
votes
2answers
2k 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 ...
1
vote
2answers
3k views

Maximally symmetric spaces

In GR, what is the most precise definition of a maximally symmetric spacetime? Also, we study about the temporal boundary of dS space, and a spatial boundary of AdS space, but aren't these spaces ...
0
votes
0answers
90 views

De sitter spacetime and co-ordinates

I was recently looking at de - Sitter spacetime and I relaized that there are many different parameterizations possible, each of which has it's own advantages. Can someone help me out and list the ...
4
votes
2answers
830 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 ...