All Questions
71
questions
11
votes
3
answers
2k
views
What is the exact meaning of homogeneity in cosmology?
I understand that, in general, homogeneity is the physical attribute of being uniform in composition (" of the same form at every point"), but I'm slightly confused when it is used in cosmology as ...
- 3,063
0
votes
1
answer
127
views
Isotropy of 3-space and spacetime metric
The most general spacetime metric is given by $$ds^2=g_{\mu\nu}dx^\mu dx^\nu=c^2dt^2+g_{0i}dtdx^i+g_{ij}dx^i dx^j.$$
Why is the second term said to violate isotropy of 3-space?
It is true that ...
- 26.8k
5
votes
2
answers
3k
views
Why isn't our universe symmetric?
Why were random variations introduced in the spherically symmetric universe after Big Bang which made it non-symmetrical. Since the outcome of a coin toss depend on factors such as torque applied, air ...
- 297
6
votes
2
answers
334
views
How can we differentiate between matter and antimatter? [duplicate]
For instance if there was a galaxy, assume it to be made up of antimatter (isolated from other "normal" galaxies), how would we, or rather, would we be able to distinguish if it was made up of matter ...
- 7,319
4
votes
2
answers
5k
views
Does "Infinite Universe" Imply Infinite Mass?
In accordance with the FLRW Metric with a curverature of $k=0$ (as observationally supported by several of NASA's experiments including WMAP, Planck satellite, DASI, etc.) the universe is spatially ...
- 1,140
1
vote
2
answers
179
views
Could the universe have evolved WITHOUT the non-determinism of quantum mechanics? [closed]
(I'm going to make a few conjectures here - please answer the question in light of them as if they were true, even though of course they may be overly simplistic or wrong)
Assuming that:
the ...
- 11
12
votes
2
answers
843
views
Do the standard cosmology models spontaneously break Lorentz symmetry?
In standard cosmology models (Friedmann equations which your favorite choice of DM and DE), there exists a frame in which the total momenta of any sufficiently large sphere, centered at any point in ...
- 1,869
3
votes
1
answer
311
views
Time Energy symmetry in General Relativity (not asking about energy conservation)
In General Relativity is there a TE symmetry similar to CPT symmetry in the Standard Model ? It's pretty easy to understand that by flipping charge and parity you merely get a time reversed equivalent ...
- 1,869
2
votes
1
answer
3k
views
Is the total angular momentum of the universe zero? [duplicate]
I know that having a net angular momentum will contradict isotropy of the universe by preferring a specific direction. But is there any experimental data on the total angular momentum of the universe ...
- 6,004
1
vote
0
answers
336
views
Spontaneous symmetry breaking by axions?
I am just reading at the beginnin of this nice article, that axions could be responsible for spontaneously breaking of a symmetry in the early universe.
Does anybody know which symmetry is alluded to ...
- 9,581
2
votes
2
answers
360
views
What are the limitations of the FLRW metric?
I was wondering, given how in any other area of life making an explosion spherically symmetric is more or less impossible is there any reason to expect that the universe is? I appreciate that the FLRW ...
- 311