All Questions
93
questions
0
votes
0
answers
66
views
No symmetries in the universe at the Big Bang...?
I apologize in advance if this is a stupid question but...
According to some scenarios about the beginning of the universe (namely cosmological inflation), in layman terms, everything was born out of ...
- 2,462
2
votes
2
answers
175
views
Do the Klein bottle and torus topologies break the Lorentz invariance?
According to this preprint, it seems that there are topologies (like the Klein bottle and the torus) that break some symmetries (like the Lorentz and translation invariances).
Is this right? Can they ...
- 2,462
0
votes
0
answers
44
views
Effects of anisotropy and non-homogeneity in the universe's symmetries...?
I was reading Philip W Anderson's essay "More is Different" (https://www.tkm.kit.edu/downloads/TKM1_2011_more_is_different_PWA.pdf) and at some point he links the isotropy and homogeneity of ...
- 2,462
0
votes
0
answers
62
views
Spacetimes where symmetries vary from place to place?
Are there spacetimes or metrics where symmetries (like Poincaré, Lorentz, diffeomorphism, translational... invariances) are only local and the symmetries of one local neighbourhood are not, a priori, ...
- 2,462
3
votes
2
answers
158
views
Are there non-smooth metrics for spacetime?
I found this statement in a discussion about the application of local Lorentz symmetry in spacetime metrics:
Lorentz invariance holds locally in GR, but you're right that it no longer applies ...
- 2,462
1
vote
1
answer
81
views
What if the universe was not uniform...?
In this popular science article, they say that if our universe resulted to be non-uniform (that is highly anisotropic and inhomogeneous) then the fundamental laws of physics could change from place to ...
- 2,462
0
votes
0
answers
87
views
Spacetimes, metrics and symmetries in the theory of relativity?
I was discussing this paper with a couple of physicists colleagues of mine (https://arxiv.org/abs/2011.12970)
In the paper, the authors describe "spacetimes without symmetries". When I ...
- 2,462
1
vote
1
answer
112
views
Symmetries changing depending on spacetime?
Just as the Lorentz symmetry holds globally in Minkowski spacetime, could the opposite also occur? That is, are there any spacetimes where the Lorentz symmetry would be broken (locally, not just ...
- 2,462
3
votes
1
answer
212
views
Is spacetime flat inside a rotating hollow sphere in general relativity?
Newton himself proved the Shell theorem, stating that inside a hollow sphere there is no gravitational force on a point mass. This theorem relies on the fact that Newtonian gravity falls off like $1/r^...
- 9,910
0
votes
1
answer
105
views
If the universe is infinite, would it be homogenous?
I know, that we can't really know the answer to that, but what is the current state of understanding?
We seem to assume that on very large scales, the universe is homogenous. As I understand it, this ...
- 866
1
vote
0
answers
50
views
Does a system with translational symmetry implies that space is homogeneous?
In my classical mechanics course, we sometimes described a system to have translational symmetry, and other times we said that it is homogenous in space and isotropic. While I know they are different, ...
- 31
1
vote
1
answer
136
views
Is the non-simply connected version of AdS space a maximally symmetric spacetime?
A common construction of anti-de Sitter space is the following:
Start with the flat five-dimensional manifold with metric $ds_5^2 = -du^2 - dv^2 + dx^2 + dy^2 + dz^2$.
Consider the hyperboloid ...
- 48.4k
0
votes
0
answers
42
views
Commutation relation of $P^{\mu}$ with fermion field $\psi(x)$
On Giunti and Kim's book "Fundamentals of neutrino physics and astrophysics", page 38-39, the book is trying to derive the commutation relation of $P^{\mu}$ and $\psi(x)$.
Begin with:
$$ U\...
- 1,421
0
votes
1
answer
121
views
Off-diagonal elements of the metric tensor and reversal symmetries
Given a metric that may be written as in some suitable coordinate system as $g_{\mu0}=\delta_{\mu0}$ and arbitrary other components, what properties of the spacetimes described by this kind of metric ...
- 103
1
vote
1
answer
90
views
How to map a complex plane Mobius transformation to 1+1D Minkowski real plane?
So consider the $(x,t)$ plane endowed with the minkowski metric, namely:
$$ds^2 = dx^2-dt^2.$$
It is well known that we can Wick rotate the time coordinate to get to the Euclidean metric. This can be ...
- 2,296