All Questions
71
questions
1
vote
2
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123
views
Is the FRW metric, based on spatial homogeneity and isotropy, rotationally and translationally invariant? If so, how?
The spatial part of the Minkowski metric, written in the Cartesian coordinates, $$d\vec{ x}^2=dx^2+dy^2+dz^2,$$ is invariant under spatial translations: $\vec{x}\to \vec{x}+\vec{a}$, where $\vec{a}$ ...
- 11.8k
4
votes
1
answer
186
views
Is gravitational particle production due to symmetry breaking?
A well-known fact about QFTs in curved spacetimes is that there is a phenomenon of particle production in expanding universes, these being described by the line element $$ds^2=-dt^2+b^2(t)d\vec x^2.$$
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- 495
2
votes
1
answer
78
views
Why must the components $g_{0i}$ of an isotropic, homogeneous spacetime metric vanish?
In Daniel Baumann's book on Cosmology, it says that the metric of an isotropic, homogeneous spacetime must have the form $$\mathrm{d}s^2=-\mathrm{d}t^2+a^2(t)\gamma_\mathrm{ij}(x)\mathrm{d}x^\mathrm{i}...
- 1,187
-1
votes
1
answer
40
views
The centre of what we can now see in the universe
If the JWST has just discovered the furthest away galaxies in one place we can now triangulate to where the centre of what we can see
This is observable and appears not symmetric with everything ...
0
votes
1
answer
146
views
Do symmetries indicate that laws of physics are invariant?
Concerning symmetry in fundamental physics, it is usually said that symmetry indicates that laws of physics are invariant independently of something
For example, time translational symmetry indicates ...
- 2,466
2
votes
1
answer
100
views
Topological phase transitions for the whole universe...?
Physicist Grigory Volovik has put forward some ideas about the universe undergoing a topological phase transition (especially in the early stages of the universe). He published a book called "The ...
- 2,466
1
vote
2
answers
138
views
Isotropic Vs. Homogeneous Universe
I know that the cosmological principle states that the universe is both isotropic and homogeneous, but I was wondering if these both had to exist at the same time? Is there a way that the universe ...
- 11
0
votes
0
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66
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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 ...
- 2,466
0
votes
2
answers
121
views
Quantum fluctuations and symmetries?
While reading this piece about symmetry breaking, in section 3 I came across the term "anomalous symmetry breaking", which happens when a symmetry is broken by quantum fluctuations:
Let us ...
- 2,466
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 ...
- 2,466
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, ...
- 2,466
1
vote
0
answers
43
views
Could inhomogeneties and/or topological defects break the fundamental symmetries of the universe?
I have heard that some types of inhomogeneties and topological defects (like cosmic strings) in cosmology have been proposed to be able to break fundamental symmetries of nature such as the Poincaré, ...
- 2,466
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 ...
- 2,466
0
votes
0
answers
86
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 ...
- 2,466
0
votes
1
answer
95
views
Could the fundamental symmetries of a fundamental theory of everything be explicitly broken, somehow?
If our universe was fundamentally described by a theory of everything (let's say e.g. string theory) it would have a set of fundamental symmetries (which would correspond to the fundamental symmetries ...
- 2,466