All Questions
Tagged with terminology spacetime
32
questions
4
votes
4
answers
826
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Why do we call the Riemann curvature tensor the curvature of spacetime rather than the curvature tensor of its tangent bundle?
I was studying the mathematical description of gauge theories (in terms of bundle, connection, curvature,...) and something bothers me in the terminology when I compare it with general relativity.
In ...
- 123
1
vote
0
answers
101
views
What is a hypersurface?
What is the concept of hypersurface in general relativity? I know it could be characterized into three categories but how do we define hypersurface (in general) in physics? I didn't get what thing it ...
- 59
1
vote
1
answer
82
views
What is a "timelike half-curve"?
I know what a timelike curve is. But what is a time-like half-curve, as in the definition of a Malament-Hogarth spacetime (below), which appears in this paper?
Definition: A spacetime $(M,g)$ is ...
- 121
-3
votes
2
answers
111
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There is time-wave?
I was thinking that for the wave equation of a wave $u(x,t)$ and $c>0$:
$${\partial^2 u\over \partial t^2}=c^2{\partial^2 u\over\partial x^2}$$
besides the solution $$u(x+ct)+u(x-ct),$$ one can ...
- 111
1
vote
1
answer
4k
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What does it mean to say the universe is not locally real? [duplicate]
Pardon me if this is a naive question.
What is difference between saying space-time is not locally real, and saying it is not real?
The proposal that the universe is not locally real seems to imply ...
- 231
3
votes
2
answers
368
views
Confusion about near-identical terms: gravity, gravitation, gravitational force - are they all the same?
As my other questions also point out, I study this for fun. I am in no university yet.
as the title (hopefully summarizes), my question is this:
is these words(or terms,) the same?
gravity
...
- 398
2
votes
2
answers
622
views
Confused on the types of solutions to Einstein field equations in General Relativity
Context
While reading about the types of solutions to The Einstein Field Equations in General Relativity, I came across the following article.
Where they explain that Karl Schwarzschild provided the ...
- 398
2
votes
3
answers
82
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Is there a standard name for Robb's spacetime invariant equation?
I'm not sure exactly how to categorize Robb's treatment of the spacetime interval. But it seems like a gem of simplicity and insight.
The following illustrations are based on MTW Box 1.3. As drawn, ...
- 2,015
0
votes
1
answer
941
views
Minkowski vs. Lorentz metric
Can anyone help me to understand the difference between Minkowski and Lorentzian metric?
They appear to me to be the very same: $$\langle x,y\rangle=-x_1\cdot y_1+x_2\cdot y_2+\ldots+x_n\cdot y_n.$$
...
- 255
0
votes
0
answers
37
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Name of "coordinate representation" of spacetime symmetries
I would like to know the name of the following "natural" representation for symmetry groups that can be realized as spacetime symmetries. The easiest example is for instance the translations ...
- 2,296
5
votes
1
answer
1k
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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 ...
- 8,650
1
vote
3
answers
173
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What is the correct name for the 4-space of special relativity
I refer to the 4-space commonly used to describe event-points $(x_0,...,x_3)$. A massive particle traces out a time-like path in such a space, since it cannot travel with a speed greater than or ...
user325561
0
votes
2
answers
107
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Clarification on the words timeslice and spaceslice
I just want some clarification what the words timeslice and spaceslice mean. In so many books and papers in higher-level physics the say something like "at a constant timeslice". Does this ...
- 563
1
vote
2
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73
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Is there any mathematical meaning to words like: Event or Cause or Effect etc [duplicate]
If you read any text on Physics then you would reorganize after enough time that Yes language of physics (Nature) is mathematics. I'm letting this discussion to opinion-based nor some philosophy of ...
- 11.9k
29
votes
5
answers
5k
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What does the concept of an "infinite universe" actually mean?
When physicists talk about the universe being infinite, or wondering whether it is or not, what do these two options actually mean? I am not interested whether the universe is infinite or not, I am ...
- 406