Questions tagged [de-sitter-spacetime]
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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?
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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
$$ ds^...
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How to check if some metric has a particular type of geodesics?
For instance, we want to know if cylindrically symmetric de Sitter-type spacetime has an axial geodesic.
This is the metric I am interested in
$$ds^2= \cos^{\frac{4}{3}}\left(\frac{\sqrt{3 \Lambda}}{2}...
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1answer
65 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 ...
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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 $\...
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70 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
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2answers
100 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 ...
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1answer
60 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 ...
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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 ...
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335 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}{\...
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109 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 ...
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How does supersymmetric de Sitter algebra in $d=3$ spacetime dimensions look like?
The de Sitter algebra ( $SO(d,1)$ in $d$ spacetime dimension) cannot be supersymmetrised as an $\mathcal{N}=1$ superalgebra due to the fact that it does not satisfy Jacobi's Identity. But in general ...
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1answer
254 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 ...
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1answer
70 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{\...
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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 ...
5
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1answer
178 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 "...
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1answer
68 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-...
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Would a repulsive black hole interior expand along with the horizon or into a Wheeler's bag of gold?
Consider an embeded de Sitter space inside the Schwarzschild interior with negative energy density (repulsive). It is clear that it would not collapse but bounce. Does it bounce into a bag of gold (...
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19 views
Differential mass formula for de Sitter metric
I'm trying to write down a differential mass formula for the de Sitter metric, analogously to how Bardeen, Carter and Hawking did it in "The Four Laws of Black Hole Mechanics" but I'm running into ...
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1answer
93 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 ...
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58 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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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 ...
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1answer
128 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
207 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 - \...
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2answers
189 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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34 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)?
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36 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 ...
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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)?
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40 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.
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1answer
255 views
Minkowski space vs De Sitter Space
Can you explain to a layman the differences between the former two?
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95 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 ...
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77 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 ...
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0answers
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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 ...
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4answers
239 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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31 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.$$ I want to find the ...
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56 views
deSitter spacetime metric and curvature
I have to compute the metric of an hyperboloid given by $-(X^0)^2+(X^1)^2+(X^2)^2+(X^3)^2=H^{-2}$ in 5D Minkowski spacetime using the following coordinates:
$$X^0=H^{-1}\sinh(Ht)\sqrt{1-H^2r^2}$$
$$X^...
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1answer
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$dS^d$ 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....
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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
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1answer
528 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 ...
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1answer
101 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, ...
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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 ...
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0answers
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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 ...
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2answers
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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 ...
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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 ...
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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 ...
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2answers
708 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 ...
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1answer
55 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 ...
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2answers
258 views
Is the dynamics of spacetime observer-dependent?
Consider de Sitter spacetime in static coordinates:
$$ ds^2 = \Big(1- (H_\Lambda r)^2 \Big) dt^2 - \frac{dr^2}{1- (H_\Lambda r)^2} -r^2 d\Omega^2, \qquad r\lt H_\Lambda^{-1} \,. $$
This metric ...
5
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1answer
274 views
Holography on non-AdS spacetime
I have a question regarding AdS/CFT and what it teaches about our world. AdS/CFT if often treated as our best tool to explore quantum gravity, and people have worked very hard in trying to understand ...
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1answer
313 views
Issues with de Sitter Space and Conformal Field Theory
As a de Sitter universe is more convenient for cosmology, what are the current issues with a dS/CFT type correspondence? Earlier work by Strominger, seemed promising but I haven't heard of additional ...
