All Questions
17
questions
3
votes
1
answer
132
views
Cosmological perturbations and energy in an expanding universe?
I was reading an interesting book from cosmomogist Viatcheslav Mukhanov Physical Foundations of Cosmology and I had a specific question about it:
It is usually said that energy conservation is ...
- 2,462
-5
votes
2
answers
229
views
If entropy increases with time, are humans' thoughts becoming more random as time increases? [closed]
If entropy increases with time, are humans' thoughts becoming more random as time increases? What effect would entropy have on the brain over generations from the absolute space-time coordinate? Are ...
- 1
0
votes
0
answers
96
views
From a true vacuum to a false vacuum in expanding space?
It is known that spacetime expansion affects many aspects in the universe. For instance, due to this, a global definition of energy conservation is difficult to define.
Could this expansion affect the ...
- 2,462
0
votes
1
answer
92
views
Can we observe two galaxies (other then ours) to be receding from each other faster then the speed of light?
There are a lot of questions and answers on this site that deal with galaxies receding from us faster then the speed of light like this one:
In summary, Hubble Law: v=H(t)D, where v is recession ...
- 29k
3
votes
1
answer
199
views
Will the ever accelerating space expansion (like at the level of inflation) eventually break causality?
I have read this question:
requires that "for an action at one point to have an influence at another point, something in the space between the points, such as a field, must mediate the action&...
- 29k
16
votes
6
answers
2k
views
Question on Roger Penrose's argument on using particles as clocks
In Roger Penrose's book Cycles of Time under section 2.3 (space-time, null cones, metrics, conformal geometry), Penrose makes the following argument which states that only particles with mass can be ...
- 498
5
votes
0
answers
82
views
Bargmann–Wigner equations in NP formalism
Bargmann-Wigner equations describe free particles of arbitrary spin $j$, namely
$$(-\gamma^{\mu}\partial_{\mu}+m)_{\alpha_r \alpha_{r’}}\Psi_{\alpha_1,..,\alpha_{r’},...,\alpha_{2j}}=0$$
where we have ...
- 341
1
vote
1
answer
73
views
What is Quantum Cosmology [closed]
I understand that quantum behavior is only apparent on the microscopic level, what then is the subject of Quantum Cosmology?
0
votes
0
answers
49
views
What are the more important effects or consequences of gamma-ray bursts for the cosmos?
I would like to know what are, in general, the consequences/effects of the known gamma-ray bursts. I refer gamma-ray bursts from the Wikipedia Gamma-ray burst that shows how are classified and the ...
2
votes
0
answers
72
views
Would the nightsky be bright (filled with starlight) without accelerating space expansion?
As I currently understand, if a photon was emitted from a far away point in the Universe, beyond the event/particle horizon, so that the space inbetween the emitter and us is expanding faster then ...
- 29k
1
vote
3
answers
202
views
What is the result that that differs by many orders of magnitude between QM and GR? [duplicate]
It is well known that QM and GR are deemed incompatible due to a discrepancy in some calculations which I have read can differ by large magnitudes. What are these calculations to which people are ...
- 145
2
votes
0
answers
98
views
What's the difference, if any, between Soft Hair & Quantum Hair
In the early 90s, John Preskill, Sidney Coleman, Frank Wilzcek and Lawrence Krauss presented a series of papers [1][2][3] on Quantum Hair on Black Holes due to Cosmic strings in a number of ways ...
- 425
1
vote
1
answer
182
views
Can the universe have different ages?
There is a similar question on here, but I figured this focuses on a more specific aspect. My apologies if it is seen as a duplicate. I am not a cosmologist. I do have a background in physics, ...
- 1,062
1
vote
1
answer
42
views
Lifting an analogy of a pond to question signals at natural or artificial boundaries in space-time [closed]
I conjured up an idea to lift an analogy into the language of QFT and GR. I thought up the universe as a pond with a liquid. If we imagine a liquid poured into some pond (sort of bang and inflation ...
user37343
1
vote
0
answers
23
views
Are atomic energies increasing as the Universe expands? [duplicate]
Starting from the FRW metric (for simplicity flat space, radial direction only):
$$ds^2=-c^2dt^2+a(t)^2dr^2$$
If we take $dt=0$ then the proper distance $ds(t)$ between two spatially separated ...
- 5,925