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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Why doesn't Galilean relativity lead to a contradiction in SR?
Two identical spaceships commanded by Alice and Bob are at rest next to each other in outer space. The clocks of the spaceships are synchronised; and when they are close by Alice can see Bob's clock ...
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Lectures on wormholes
I am currently writing a review as a thesis project and I must cover black holes and wormholes, static and stationary. For black holes I found this lecture where black holes are approached from a more ...
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Where does the negative signature case come from in the Pythagorean derivation of distances in spacetime?
I am reading Why does $E=mc^2$ (and why should we care?) by Brian Cox and Jeff Forshaw. I want to understand these three sentences
(from page 76/77):
Once we follow Occam and make these two ...
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Time dilation query [closed]
In the light clocks, time ticks via the motion of light and since speed of light is constant therefore when the clock is in motion ,the photon has to cover a greater distance by the perspective of an ...
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What exists in the world according to the special relativity? [closed]
Before I learned about special relativity, I thought that only one 3-dimensional state of the world exists. Then, like in game of chess, in one "turn" previous state is destroyed - and the ...
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Differences and similarities between $\mathbb{R}^4$, $\mathbb{R}^{1,3}$, $T_p\mathbb{R}^4$, and $T_p\mathbb{R}^{1,3}$
Consdier $\mathbb{R}^4$ with Cartesian coordinate and $\mathbb{R}^{1,3}$ with spacetime coordinates. Also consider their corresponding tangent spaces $T_p \mathbb{R}^4$ and $\mathbb{R}^{1,3}$, ...
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Are branes topological defects? How else could they be physical?
As far as I understand, the branes of brane cosmology are lower-dimensional "sub-manifolds" of some space. It was hard to imagine for me how such structure could exist and be physical. But ...
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Diameter of a sphere in the regime of general relativity
Lets start naive: empty space, define the origin somewhere, start putting mirrors in a distance of $r$ in many directions so that they roughly sample the surface of a ball of radius $r$.
Someone ...
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Internal and external Einstein equation from warped spacetime metric
If I have a $D$ dimensional manifold, with Einstein equation
$$R_{MN} - \frac{1}{2}g_{MN}R = T_{MN}$$
and, as a solution, a warped metric, with d external dimension (denoted using greek indices $\...
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Geometrically Impossible Spacetime
A result in math says that $S^n$ carries a Lorentzian metric iff $n$ is odd.
Using it we can observe that a 2-sphere spacetime is impossible, a 3-sphere spacetime is geometrically possible, but again ...
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Energy and momenta of a field on a curved manifold
In a curved spacetime with metric $g$, let us have a complex scalar field $\Phi$. The stress energy momentum tensor of the field is defined as,
$$T_{ab} := \frac{-2}{\sqrt{-g}} \frac{\delta S_\Phi}{\...
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What symbol is used for 'proper distance'? [closed]
Proper time and proper space are generally defined as what an observer would measure in their own rest frame. If $\tau$ is a commonly used symbol for the proper time, what is the corresponding symbol ...
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Can we see the rest-energy of a mass as its kinetic energy in the $ct$-direction?
A mass $m$ at rest has an energy $E=mc^2$. Can we say this is its kinetic energy in the $ct$-direction?
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Could the universe be a topological defect in a higher space?
I am a mathematician with an undergrad understanding of physics. I recently learned of topological defects in quantum fields. It is an intriguing idea that there could be regions in our universe that, ...
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Does special relativity imply that there's such a thing as absolute time, or base time?
If time measured by one observer moving at a greater velocity than another observer is observed to be passing more slowly, does this imply that there's such a thing as "absolute time" or &...
