Questions tagged [de-sitter-spacetime]

The tag has no usage guidance.

Filter by
Sorted by
Tagged with
3 votes
1 answer
118 views

de Sitter space vs de Sitter universe

I have heard of the term de Sitter space. From this post user G. Smith writes, De Sitter spacetime is curved; specifically, it has the same positive scalar curvature at every point. Likewise, when I ...
user avatar
1 vote
0 answers
58 views

Positive and negative curvature de Sitter spacetimes

I'm reading Mukhanov's "Physical foundations of cosmology" and in the section on the de Sitter universe, he examines a perfect fluid with pressure $p$ equal to negative of the energy density ...
user avatar
3 votes
0 answers
44 views

Double Wick Rotation of de Sitter Metric with Closed Slicing

The de Sitter spacetime (with closed spherically symmetric slicing) has the metric $$\text{d}s^2 = -\text{d}t^2 + \alpha^2\cosh(t/\alpha)^2\text{d}\Omega_{d-1}^2$$ where $\text{d}\Omega_{d-1}^2$ is ...
user avatar
  • 621
2 votes
0 answers
52 views

Negative surface tension of de Sitter event horizon?

Questions – What does a negative surface tension of a de Sitter cosmological event horizon actually mean? Scotch in water, or something else? What does a zero ‘external’ vacuum pressure to the de ...
user avatar
  • 1,085
1 vote
0 answers
51 views

Confusion with timelike geodesics in de Sitter space

Without deriving the whole geodesic, I'm thinking I should be able to qualitatively see how the geodesics will curve just by looking at the connection coefficients. Given the static coordinates $$ds^...
user avatar
  • 1,383
1 vote
0 answers
51 views

F-theory questions on MSSM vs. SM compatibility and on de Sitter vacua

Having read https://arxiv.org/abs/2112.03947, https://arxiv.org/abs/1903.00009 and https://arxiv.org/abs/1903.00009, I noted the use of MSSM (Minimal Supersymmetric Standard Model) as if equivalent to ...
user avatar
1 vote
1 answer
112 views

Can we glue the Schwarzschild and the de Sitter metrics at their event horizon?

Is there a way to glue the de Sitter metric inside the event horizon of the Schwarzschild metric, without an explicit reference to a particular coordinates system? Using the standard radial ...
user avatar
  • 6,676
2 votes
1 answer
82 views

Is the number of possible values of a quantum observable finite, countably infinite or uncountably infinite?

Do we know, or have a theory about, whether the number of possible values any fundamental quantum property can assume upon observation is finite, countably infinite or uncountably infinite?
user avatar
4 votes
0 answers
63 views

Can a massless electric charge particle exist in a de Sitter universe?

Because of the cosmological constant, our universe may reach a de Sitter universe in the far future. If we suppose this, the most basic group of particle physics will be the Sitter, rather than ...
user avatar
  • 41
0 votes
0 answers
45 views

Holographic Degrees of Freedom

What does it mean when one says "holographic degrees of freedom" in dS space? As Susskind does in his recent papers, the latest here (page 18).
user avatar
2 votes
3 answers
571 views

Why do string theorists seem to ignore cosmology?

Related and sort of a follow-up question to: If string theory is inconsistent with observations, why hasn't it been rejected yet? From the answer to that question, string theorists are aware the ...
user avatar
  • 16.2k
0 votes
1 answer
85 views

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 ...
user avatar
  • 1,383
0 votes
0 answers
46 views

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 ...
user avatar
2 votes
0 answers
52 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 ...
user avatar
1 vote
0 answers
46 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,...
user avatar
  • 1,383
0 votes
1 answer
45 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-...
user avatar
  • 886
0 votes
2 answers
347 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+\...
user avatar
  • 883
2 votes
1 answer
173 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 ...
user avatar
2 votes
0 answers
59 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 ...
user avatar
3 votes
2 answers
621 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^...
user avatar
1 vote
0 answers
46 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}...
user avatar
  • 11
2 votes
1 answer
521 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 ...
user avatar
  • 4,070
3 votes
0 answers
124 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 $\...
user avatar
3 votes
0 answers
105 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 $...
user avatar
6 votes
2 answers
215 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 ...
user avatar
2 votes
1 answer
191 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 ...
user avatar
1 vote
0 answers
23 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 ...
user avatar
  • 2,691
5 votes
0 answers
374 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}{\...
user avatar
1 vote
1 answer
262 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 ...
user avatar
2 votes
1 answer
293 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 ...
user avatar
0 votes
1 answer
141 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{\...
user avatar
3 votes
0 answers
176 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 ...
user avatar
  • 5,281
7 votes
1 answer
261 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 "...
user avatar
1 vote
1 answer
149 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-...
user avatar
0 votes
1 answer
200 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 ...
user avatar
  • 11
1 vote
0 answers
61 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 ...
user avatar
  • 113
2 votes
1 answer
283 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 ($\...
user avatar
  • 6,676
6 votes
1 answer
375 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 - \...
user avatar
  • 6,676
5 votes
2 answers
343 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 ...
user avatar
  • 6,676
1 vote
0 answers
54 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)?
user avatar
  • 131
2 votes
1 answer
230 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 ...
user avatar
0 votes
1 answer
40 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)?
user avatar
  • 10.6k
1 vote
0 answers
72 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.
user avatar
  • 10.6k
2 votes
1 answer
684 views

Minkowski space vs De Sitter Space

Can you explain to a layman the differences between the former two?
user avatar
  • 131
0 votes
1 answer
121 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 ...
user avatar
  • 10.6k
0 votes
0 answers
122 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 ...
user avatar
2 votes
0 answers
39 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 ...
user avatar
2 votes
4 answers
382 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 ...
user avatar
  • 445
0 votes
0 answers
53 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 ...
user avatar
  • 197
0 votes
0 answers
76 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^...
user avatar
  • 77