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.
337
questions
0
votes
2
answers
70
views
Do we have notion of a proper time for any two timelike separated arbitrary events?
Consider two infinitesimally close, timelike separated but otherwise arbitrary events $P$ and $Q$ with coordinates $(t,\vec{x})$ and $(t+dt,\vec{x}+d\vec{x})$. For example, imagine event $P$ is "...
- 11.7k
1
vote
2
answers
199
views
Is time inflating proportionally to space?
We know space is expanding at a rate of roughly 432 miles/light-year/year. Since Einstein showed that time was intrinsically linked into the 4 dimensional structure of spacetime one would logically ...
- 341
0
votes
1
answer
103
views
Terminology: Is it correct to refer to the spacetime interval as "absolute distance?"
...Because it's Lorentz-invariant.
Different inertial frames observe different distances, durations, and simultaneity. They even report a different time of day on their wristwatch. But everyone in any ...
- 279
3
votes
1
answer
734
views
How many null directions are there?
The metric signature of spacetime is usually given as ($3,1$), but spaces can also be ($3,n,1$). Null surfaces include photons and event horizons, which exist, so is $n$ actually $ > 1$ in the ...
- 279
0
votes
2
answers
65
views
Unidirectionality of Time in Spacetime
I have a question regarding the dimension of time. We all know that an event in spacetime is defined by a point
$$ {x}^{u} = (ct, x, y, z) .$$
The only component that breaks the symmetry is $ct$, ...
- 151
1
vote
2
answers
117
views
Curvature of space from approaching gravity sources affecting observations of expansion
Since gravity curves space, I wonder how the locally increasing density of matter and energy due to the current galactic mergers with the Milky Way affects our perception of the universe.
Basically, ...
1
vote
1
answer
56
views
Lorentz transformation of basis vectors in The geometry of Minkowski spacetime by Gregory L. Naber
Gregory L. Naber's book introduces the Lorentz transformation like this:
Now let $L :M→M$ be an orthogonal transformation of $M$ and
${e_1, e_2, e_3, e_4}$ an orthonormal basis for M. By Lemma 1.2.3, ...
- 11
18
votes
2
answers
3k
views
How does spacetime curve around an object in superposition?
I'm trying to learn quantum mechanics and this is a question that came to mind. I tried searching for it online, but I couldn't find a good answer (or at least one I could understand). From what I ...
- 191
0
votes
1
answer
173
views
Can momentum exist in a null direction?
CONTEXT (skip to "my question is"):
As I understand it, and correct me if I'm wrong, an orbit trades momentum between the X and Y directions. But spacetime can have negative and even null ...
- 279
2
votes
1
answer
124
views
Could the universe have a form of a $T^3$-torus?
Cosmological measurements suggest that we live in a flat universe. However, what might be less clear is its topology. So could the flat universe have the form of a $T^3$-torus, i.e. the torus whose ...
- 9,778
1
vote
1
answer
81
views
Do we still not know whether the universe had a beginning? [duplicate]
The Question:
According to Prof. Brian Cox in the first 30 seconds of this YouTube video from 4 years ago, we do not know whether the universe had a beginning. Is it still the case that we do not ...
- 105
-4
votes
2
answers
141
views
What model tells us there is nothing outside the universe?
Is there an existing model or theory that shows there is nothing outside of the universe that interacts with anything inside the universe? Or to put it in other words, is there a model or theory ...
- 4,783
0
votes
0
answers
29
views
Does the Existence of Planck Units Suggest Discontinuity in Time and Space? [duplicate]
I’ve posed the following inquiry on Philosophy Stack Exchange:
Can the idea of continuity make sense in the real world?
A summary of it is presented here:
Continuity in mathematics means no jumps or ...
user397166
1
vote
2
answers
134
views
Keplerian Frequency of Schwarzschild Black hole
The Keplerian frequency/ Orbital frequency is the inverse of orbital period and for Schwarzschild black hole it is given by $$\frac{1}{2\pi}\sqrt{\frac{M}{r^3}}.$$ its unit is Hertz. Now To express ...
- 21
0
votes
1
answer
59
views
Are gravitons suggested as the cause of matter curving space?
My understand is that GR says that mass curves space but it does not say why or how this occurs. Is the idea of gravitons that they are the entities that actually affect space?
- 2,238