The study of the large-scale structure, history, and future of the universe. Cosmology is about asking and answering questions about the "big picture" - the extent, origin, and fate of everything we know.
2
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1answer
83 views
If the nucleation bubble radius is greater than the deSitter radius, does that make the de Sitter space stable?
In our de Sitter phase, the cosmological constant is tiny. $10^{-123}M_P^4$. Suppose there is another phase with a lower vacuum energy. Is de Sitter phase still stable? The tunneling bubble radius has ...
2
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2answers
345 views
What is the difference between parallel universe and multiverse?
What is the difference between parallel universe and multiverse? Is it parallel universe or universes?
2
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1answer
102 views
variations of Einstein equations with conversion between gravitational and non-gravitational energy
I'm looking for existing papers studying a variation to Einstein equation that does not rely on the annoying matter conservation identity:
$$ T_{\mu \nu; \nu} = 0 $$
And instead tries to equate the ...
-1
votes
1answer
148 views
What if microstates increase proportional to universe volume?
I am probably a delusional crank with a lot of crazy, overly speculative conjectures. If I am not delusional, than at the very least I've been ahead of the curve, the last 40 or so years. I was a ...
0
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1answer
52 views
Can anything come out from the big bang?
If any configuration of matter can fall into a black hole and hit the singularity, and ditto for the big crunch, and there is time reversal CPT invariance, does it mean anything can pop out of the ...
2
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4answers
188 views
Space Expansion vs. Relative Motion
Inspired by a recent dialogue from another question:
Given 2 objects moving at some velocity $v$ relative to one another, is it possible to determine whether they are moving or whether the space ...
1
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0answers
57 views
Thermal gravitational radiation and its detection
To my poor knowledge on the topic, the gravitational waves that are most likely to be detected by LIGO or other experiments do not have thermal spectrum. But I'm not certain.
I know that Hawking's ...
4
votes
3answers
147 views
Could dark energy be powered by force particles that obey quantum mechanics?
From what (little) I know about physics, I understand that the universe is expanding due to dark energy, and I understand that no one quite understands it yet. I also understand that the cosmic ...
1
vote
1answer
322 views
Does the large red shift value of galaxies mean they are far away?
When the red shifts of galaxies are large, why do we think that they are far away?
I know about Hubble's law, Tully-Fisher relation of spiral galaxies, Faber-Jackson relation of elliptical ...
2
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0answers
253 views
Is large-scale “time reversal” (Poincaré recurrence) possible given infinite time?
The following are some assumptions I'm basing my question on, from what (little) I understand of physics. I list them so an expert can (kindly) tell me where I'm going wrong.
There is a probability ...
3
votes
4answers
336 views
As the universe expands, why do some things stretch but not others?
I got into watching a video on Olbers' Paradox a few days ago, and from there read about the origins of the universe, its expansion, and so on... it's always fascinated me, but now something about it ...
2
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0answers
67 views
Is eternal inflation Lorentz invariant?
Start without general relativity. Consider a metastable vacuum over good ol'-fashioned Minkowski space. It decays. A bubble forms and the domain wall expands. The domain wall is timelike, and ...
0
votes
1answer
74 views
Cosmological constant of standard model of cosmology and observational data
I am curious whether the current Lambda-CDM model of cosmology matches well with observational data, especially expansion of the universe.
How well does Lambda-CDM defend its established status from ...
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2answers
139 views
Possibility of making dark energy equivalent with dark matter
I was curious whether it is possible to make dark energy equivalent to dark matter.
Can this unification be done?
If it can, why do scientists prefer to separate dark energy from dark matter?
5
votes
3answers
373 views
Will the Big Rip tear black holes apart?
There seems to be an obvious contradiction between the predictions of the physics of black holes and the Big Rip, a predicted event about 16.7 Gyr in the future where local groups, galaxies, solar ...
2
votes
2answers
177 views
Was Planck's constant $h$ the same when the Big Bang happened as it is today?
Was Planck's constant $h$ the same when the Big Bang happened as it is today?
Planck's constant :
$$h= 6.626068 × 10^{-34}\, m^2 kg / s,$$
$$E=n.h.\nu,$$
$$\epsilon=h.\nu$$
1
vote
1answer
82 views
How precisely can we date the recombination?
The early universe was hot and opaque. Once it cooled enough, protons and electrons were able to form hydrogen atoms. This made the universe transparent, and was known as recombination. We can see the ...
0
votes
1answer
805 views
Why aren't we Boltzmann brains in an infinite universe?
Either space is compact, or it is infinite. If space is infinite in extent, either it is thermal over an infinite volume, or it is in the vacuum state for most of it. If it is thermal, infinity is a ...
3
votes
2answers
118 views
Shouldn't LHC have used $p\bar{p}$ collisions, instead of $pp$ collisions, to study baryogenesis?
Baryogenesis is the physical process(es) that produced baryon antibaryon asymmetry in the early universe. That means, the laws that governed the bigbang was baryon-antibaryon symmetric.
On the other ...
3
votes
2answers
1k views
Size of universe after inflation?
Wikipedia states the period of inflation was from $10^{-36}$sec to around $10^{-33}$sec or $10^{-32}$sec after Big Bang, but it doesn't say what the size of the universe was when inflation ended. ...
10
votes
2answers
348 views
Can $10^{23}$ stars be treated with methods of statistical mechanics?
Statistical mechanics is used to describe systems with large number of particles ~$10^{23}$.
The observable universe contains between $10^{22}$ to $10^{24}$ stars. Can we treat those many stars as a ...
1
vote
1answer
465 views
Relation between comoving distance and conformal time?
In cosmology, we have two quantities and I want to understand the physical relation between these two :
$\chi = \int_{t_e}^{t_0}c\frac{dt'}{a(t')}$ : the comoving distance with $t_e$ the time at ...
1
vote
3answers
153 views
Which universe had a beginning? The universe or the observable universe?
When we say the universe had a beginning, do we mean the entire universe or the observable universe? Or did both of them have a beginning?
3
votes
1answer
128 views
How could we experience multiverse through cosmic background radiation?
I'm reading a book about string theory, and it tells me in the future it could be possible to detect existence of other bubble universes through cosmic background radiation. Is this true? What could ...
0
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0answers
19 views
In the Hartle-Hawking boundary condition, what should we set as the initial values for the scalar fields?
In the Hartle-Hawking boundary condition, what should we set as the initial values for the scalar fields? Fields like the Higgs assuming it's fundamental, and the inflaton fields.
3
votes
0answers
49 views
squeezed radiation astronomy
Squeezed electromagnetic vacuum does have a renormalized energy density smaller than the vacuum. So it makes it in my opinion a inconspicuous candidate for a dark energy carrier.
Are there ...
3
votes
6answers
579 views
Does gravity slow the expansion of the universe?
Does gravity slow the expansion of the universe?
I read through the thread http://www.physicsforums.com/showthread.php?t=322633 and I have the same question. I know that the universe is not being ...
5
votes
1answer
144 views
variable speed of light in cosmology
In this paper, D. H. Coule argues that warp drive metrics, like the one proposed by Alcubierre, require the exotic matter to be laid beforehand on the travel path by conventional travel. At section 5 ...
0
votes
5answers
183 views
Is our universe the only universe out there or are there also other possible universes?
There is the specific universe we live in, the "actual" universe with planet Earth, humans evolving, and us discussing metaphysical debates on physics.se in 2012, etc. There might or might not also ...
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0answers
61 views
Reference request: FLRW with k>0, dust, and positive cosmological constant
The exact solution representing a FLRW universe with $k>0$ and dust (p=0), and $\Lambda=0$, is described by a cycloid. What is the exact solution for dust, in the presence of a positive ...
2
votes
1answer
99 views
Reference request for low entropy big bang
There is a somewhat widely accepted argument that the second law of thermodynamics exists because the universe began in a low-entropy state. I'm writing a paper that mentions this (and must be ...
3
votes
1answer
120 views
How can a deSitter space have finite size?
a deSitter space is a maximally symmetric solution of Einstein equations, I have some problem picturing one thing: this space is past and future (time) infinite but spatial slices have finite size, ...
1
vote
4answers
158 views
Can cosmic inflation be explained by matter antimatter reactions?
The big bang theory proposes that equal amounts of matter and antimatter were created in the beginning. Shortly afterwards most of it annihilated. Could that have produced enough energy to drive ...
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1answer
141 views
Higgs field existence and zero energy
If the Higgs field permeates all space, why some claim, that total universe energy equals (or is very close to) zero?
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11answers
493 views
Are there any theories that explain the very beginning of absolutely everything? [closed]
Of course there's the theory of The Big Bang, and there are theories on what caused The Big Bang, but what was the cause of the very first thing that ever happened? What started every
I also won't ...
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1answer
187 views
What does the discovery of Higgs boson mean for steady state theory?
The relationship between the steady state theory and the notion of Higgs boson is not clear to me. What does the discovery of Higgs boson mean for steady state theory? Or are the two ideas purely ...
6
votes
4answers
484 views
Is space unending?
Is the space unending, i.e it has no boundaries? If yes, how can a thing exist which is non-ending? Its impossible for me to imagine something like that. Secondly, if its not and has boundaries then ...
1
vote
2answers
72 views
$\Omega_{r}$ from WMAP results?
To do some Friedmann-Lemaître cosmology calculations, I would like to know an estimation of $\Omega_{r_0}$ ($\Omega$ radiation today). WMAP 7 give estimation of $\Omega_{b}$, $\Omega_{c}$ and ...
3
votes
1answer
193 views
Is the only diffeomorphism invariant anthropic principle the final anthropic principle?
Quantum gravity is a gauge theory with the gauge symmetry spacetime diffeomorphisms. Presumably the quantum state of our universe is invariant under spacetime diffeomorphisms, including timelike ...
1
vote
1answer
150 views
What exactly are super WIMPs?
I recently got confused (and slightly annoyed by the lack of technical details) when reading a popular article (authored by Jonathan Feng and Mark Trodden) introducing the concept of super WIMPs.
The ...
3
votes
3answers
352 views
What makes the earth keep spinning?
I am thinking of what makes the earth keep spinning. Is there anybody here know the answer?
3
votes
3answers
157 views
What does Brian Greene mean when he claims we wont be able to observe light from distant stars due to the universe's expansion?
Brian Greene in this TED talk about possible multiverse, claims tomwards the end (At around 18:00 mark) this statement. 'Because the expansion is speeding up, in the very far future, those galaxies ...
0
votes
1answer
61 views
Continuum model of the n-body problem?
Consider a collection of $n$ point masses evolving under the influence of gravity. For very large $n$, one might be interested in making a continuum approximation of this system (for cosmology, say). ...
1
vote
3answers
177 views
black body and cosmic microwave background radiation
Why is the sprectum of the cosmic microwave background radiation (or seems to be) that of a black body?
1
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0answers
115 views
How is the poincare conjecture(and perelman proof) helpful in studying the properties of the universe?
Can someone tell me how the poincare's famous conjecture or its proof by perelmen can be helpful in deciding some properties like the shape of the universe?
2
votes
1answer
96 views
extracting energy from cosmological expansion
This question is a more concrete reincarnation of an old question about energy conservation in GR.
Are there mechanisms to extract energy from the cosmic rate of expansion? putting some extremely ...
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votes
1answer
122 views
Is existence subjective or objective? [closed]
Is existence subjective or objective? There are two observers, Alice and Bob, in a de Sitter cosmology with a positive cosmological constant. Both coast along their geodesics with some initial spatial ...
0
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1answer
67 views
Regarding binary systems
Are binary systems (in case of stars and other celestial bodies) more favorable than independent existence? I've been going through an article regarding pulsars, where it was stated that 'many pulsars ...
2
votes
2answers
141 views
Was Sun a part of a binary system?
I've read that many stars and other celestial bodies are found to constitute binary systems where the two bodies spin around each other. But our Sun is one of the exceptions. Could it be possible that ...
4
votes
1answer
168 views
Will acceleration rate of expansion of space become faster than speed of light?
From watching cosmology lectures, it seems that the space between galaxies is expanding at an accelerating rate, my question is since it is the space that is (acceleratingly expanding), the special ...
