As a consequence of the Lorentz transformations, time and space transform into each other when changing reference frame. This calls for a unified description: Minkowski spacetime.
4
votes
2answers
240 views
Does the current acceleration of universe imply that our universe is open?
Does the current acceleration of universe imply that our universe is open?
If the universe is closed, from the Friedmann's equation, the acceleration of universe wouldn't be possible, would it be? (Of ...
2
votes
2answers
114 views
Does gravitational redshift imply gravitation time dilation?
The EEP is used to justify that if an observer on the ground shoots a beam of light towards a tower, then when the light reaches the tower, it will be red shifted. This is because of what happens in ...
-1
votes
2answers
412 views
Space-time hospitality
Are there any reasons to assume that organic processes cannot arise in relatively flat spacetime environments?.. An argument for the existence of a critial value or window ..
6
votes
1answer
275 views
Do spacelike junctions in the Thin-Shell Formalism imply energy nonconservation and counterintuitive wormholes?
The Thin Shell Formalism (MTW 1973 p.551ff) is used to properly paste together different vacuum solutions to the Einstein equations. At the junction of the two solutions is a hypersurface of matter – ...
1
vote
1answer
318 views
Does spacetime really exist in quantum gravity?
If there are no localized observables in quantum gravity, does spacetime really exist, or might spacetime really be an illusion?
-1
votes
1answer
117 views
the search for calabicles
Pop-sci ST books say, "At every point of space, there is a Calabi-Yau space..." or similar. But uncertainty p. and noncommgeom say, no points in space, only planckons (not my coinage). Is 'point of ...
-2
votes
1answer
109 views
Finite amount of matter and space
(Please bear with me.)
If the universe included multi-universes, and black holes transferred matter between them, AND yet there was a large, but FINITE amount of matter and space, How would that ...
-3
votes
1answer
167 views
If the universe is infinite, shouldn't I already have been contacted by a time and space travelling doppelgänger?
If the universe is infinite, by virtue of chance it means that every possible configuration of matter must exist somewhere (according to this documentary).
Therefore, if we accept that the universe ...
-6
votes
1answer
195 views
Speed of light is not fixed?
In my research, I found that the speed of light is not fixed. IS it true?
Namely, We know that light refracts when the medium it travels through changes. Actually, light travels in the same medium ...
5
votes
0answers
156 views
Penrose Conformal diagram for flat 2-dim Lorentz space-time
I have the following metric
$$ds^2 ~=~ Tdv^2 + 2dTdv,$$
defined for
$$(v,T)~\in~ S^1\times \mathbb{R},$$
e.g. $v$ is periodic.
This is the according Penrose diagram:
Question 1) Is the ...
5
votes
0answers
145 views
Energy balance of closed timelike curves in Gödel's universe
I recently read Palle Yourgrau's book "A World Without Time" about Gödel's contribution to the nature of time in general relativity.
Gödel published his discovery of closed timelike curves in 1949. ...
3
votes
0answers
76 views
How would an observer perceive movement on a train that's travelling near the speed of light?
Person A is on Earth and a train (or whatever you want to imagine) travels past him at near the speed of light. How would person A perceive movement on the ship? If time is slowed on the ship from the ...
2
votes
0answers
48 views
Naked singularity and extendable geodesics
I'm currently trying to understand the notion of a naked singularity. After consulting books by Wald and Choquet-Bruhat, it seems that for a naked singularity one must have that the causal curves can ...
2
votes
0answers
75 views
Car parking special-relavity puzzle
Hi I read the following puzzle from an old text book long time ago. However it doesn't provide the answer. So what is the solution?
Let's suppose a car is going to park to a garage and the garage is ...
2
votes
0answers
275 views
de Sitter and anti de Sitter metric
Is the following correct for the distance $d$ from the origin $(0,0)$ to point $(t,x)$ in the 2-dimensional
de-Sitter and anti de-Sitter spaces? Here, $t$ is time and the distance may be called the ...
1
vote
0answers
46 views
When is spacetime homogenous and isotropic?
When is spacetime homogenous and isotropic?
For example, some metric $g_{\mu \nu}$ is homogeneous and isotropic. We now construct effective metric
$$n_{\mu \nu} ~\rightarrow~ g_{\mu \nu} + ...
1
vote
0answers
45 views
Naked singularity and null coordinates
I'm trying to understand the notion of a naked singularity on a more mathematical level (intuitively, it's a singularity "one can see and poke with a stick", but I'm having troubles on how to actually ...
1
vote
0answers
37 views
When spacetime expands to the point where galaxy clusters are not observable, will there by any interaction?
It's my understanding that in a few billion years, clusters of galaxies won't be able to directly observe one another due to the expansion of spacetime overcoming gravity between those clusters. ...
1
vote
0answers
90 views
Higher dimensions
1) How we determine whether the higher dimensions are Unstable or Unpredictable? Or on the basis of what assumption we make this prediction?
(Source of Image: Max Tegmark. See also this Wikipedia ...
1
vote
0answers
173 views
The structure of space-time
I came across this paper recently called The Small Scale Structure of Spacetime and the following idea occured to me:
To uninformed humans the universe appears Euclidean but we know from GR that on a ...
0
votes
0answers
33 views
metric extension outside the light cone
Could anyone explain what "extending the solution" beyond the past light cone means? Say, for example, if I have a metric (no coordinate singularities), how can I extend it to the outside of the past ...
0
votes
0answers
157 views
Spacetime around a Black Hole
If we consider the sun, then space-time is curve around it. My question is that what is the kind of curvature of space and time around the black hole. Is that space and time more curved around the ...
0
votes
0answers
82 views
Alternate derivation of kinetic mass increase in special relativity, from Maudlin
I've recently come across a derivation, which I've not seen before, of mass increase in special relativity. It seems to make sense, but I get tripped-up on an intermediate step, and I can't seem to ...
0
votes
0answers
115 views
Is it mathematically possible or topologically allowable for cutouts, or cavities, to exist in a 3-manifold?
A few weeks back, I posted a related question, Could metric expansion create holes, or cavities in the fabric of spacetime?, asking if metric stretching could create cutouts in the spacetime manifold. ...
0
votes
0answers
54 views
Space-time & solar mass
Does the space-time curvature described by Einstein have any affect on the accuracy of our determination in the age of a star or globular cluster? How does this affect our interpretion of how old we ...
