Questions tagged [spacetime]
Within relativity (both special and general), changes of reference frames can change both the notions of space and of time, with one depending on the other as well. As a consequence, it is necessary to treat both concepts in a unified manner. Hence the term spacetime.
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Definition of reference system in the context of General Relativity [closed]
I'm in trouble with the definition of reference system in the context of General Relativity intended as coordinate chart (i.e. no frame field).
Various sources define it as a one-to-one smooth mapping ...
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How do gravitational waves propagate through spacetime without a medium? [duplicate]
How do gravitational waves propagate through spacetime without a medium?
I'm trying to understand gravitational waves at an introductory level, and I'm confused about how they propagate.
My confusion:
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Another modification of Twins Paradox [closed]
Twins go to open space, get on rockets, and start moving in opposite directions at constant speed. After some time they stop and connect via video call. What will they see?
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What observational constraints rule out $r_s = 2R$ as a cosmological postulate? [closed]
A geometric model I've been studying derives cosmological parameters from the postulate that the Schwarzschild radius equals twice the cosmic radius at all scales ($r_s = 2R$). It claims to resolve ...
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Triangulation of spacelike convex Polytopes into spacelike simplices
Setup
Consider $\mathbb R^n$. We consider the slope of vectors $v \in \mathbb R^n$ with respect to the first coordinate:
$$\operatorname m(v) := \frac{\vert v_1 \vert}{\Vert \pi_{\operatorname{span}(...
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Relation between the axioms of relativistic spacetime and the postulates of relativity
I am watching the course on general relativity by the WE Heraeus international winter school on gravity and light given by prof. Frederic Schuller, concretely on Lecture 13 on relativistic spacetimes ...
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Derivation of Lobachevsky metric
I am reading the book "Gravitation Foundations and Frontiers" by T. Padmanabhan.
In section 1.4.1, he derives the Lobachevsky metric using the 3D velocity space.
His derivation proceeds in ...
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Speaking of spacetime, can there be space without the time needed to traverse that space by light? [closed]
The question in context of the size of the observable universe.
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What is infinity in the real world? [duplicate]
What is infinity? It's a human invention. There is nothing in the physical world that we can point to and say: "This is infinite". And if there were, it is not certain we could prove it by ...
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Why can't you just go around the black hole to get to Quadrant III of the Kruskal-Szekeres diagram?
A Kruskal-Szekeres diagram (below) only shows one spatial dimension. If you extended it to cover two spatial dimensions, it seems like it should have a future and past cone meeting at their common ...
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Is there a typo in Wald General Relativity Theorem 8.1.6?
My contention is, didn't we just find out that $\lambda \subset I^+(C)$ contradicts that $p \in \dot{I}^+(C)$, which $p$ should fulfill by definition? Should this not be $\lambda \subset \dot{I}^+(C)$ ...
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What happens if it is proved that spacetime is continuous? [closed]
Right now we dont have the tools to test on the energies of quantum gravity, at least not directly.We can however look for light emitted a long time ago and disclose some theories.
We expect that ...
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Is there currently a theory of higher dimensions, i.e., 5 or more spacetime dimensions?
I think the question as it stands is self-explanatory. The reason I'm asking is that I have heard credible evidence of things that don't normally exist in 4-dimensional spacetime, e.g., UFOs (UAPs) ...
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On the definition of rest frame in special & general relativity
In the context of special & general relativity there exists the notion of "rest frame" w.r.t. an object or an observer.
The latter are represented in spacetime by a timelike worldline (...
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Correct expression for spatial volume element in GR
In General Relativity, what would the correct expression for an infinitesimal volume of 3D spatial "part" of spacetime look like:
is it
$$
\textrm{d}V = \sqrt{-g} \textrm{d}x^1 \textrm{d}x^2 ...
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