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.
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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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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 ...
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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
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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
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1answer
173 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 ...
2
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1answer
243 views
Does a complete theory of quantum gravity require anthropic post-selection?
Does a complete theory of quantum gravity require anthropic post-selection? Certainly the black hole complimentarity and causal patch conjectures highlights the essential role of observers, at least ...
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0answers
54 views
is cosmic expansion related with IR divergencies?
This question is related to renormalization, but in the IR limit. It is assumed that unitarity does take care of IR divergencies in interacting theories like QED. But how would one interpret ...
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0answers
61 views
Unitarity and quantum cosmology
By studying quantum cosmology I was asking myself if the fact that the universe is expanding, so space is expanding and with it I would say that phase space is also expanding, so it's a non-unitary ...
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0answers
50 views
Hipothetical universe history with power law distributed matter [closed]
As every physicist knows that the history of universe has been dominated from light, matter and vacuum. All of three are supposed uniform distributed at very large scale. What would been happened to ...
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2answers
66 views
Why is the thomson cross section constant over cosmological time?
In all astrophysical calculations I'm aware of, the thomson cross-section (for electron scattering) is taken as a constant in time, why is this the case? I have only weak experience in cosmology and ...
6
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2answers
181 views
How does universal inflation fit with the Planck length?
If the universe is undergoing inflation, and there is a minimum scale that things can exist at (the Planck length), does that mean that new Planck-sized domains have to be continuously popping into ...
1
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2answers
44 views
Locating a Comet, how is it done?
How are the comet-hunters able to precisely locate/know about the required comets ? How can they distinguish between comets from such a far distance ? How are they able to estimate the exact time ...
2
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2answers
274 views
Parabolic or Hyperbolic?
How can astronomers find the difference between a parabolic and a hyperbolic comet ? What are the criteria that helps them distinguish these ? Can a parabolic comet switch over to become a hyperbolic ...
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1answer
158 views
Density of universe during recombination
How can I calculate the density of the Universe at recombination?
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2answers
63 views
proportion of dark matter/energy to other matters/energy at the beginning of the universe
How will the proportion of dark matter/energy to other matters/energy be like at the momenets after the beginning of the universe (standard Big Bang model)?
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0answers
22 views
Expansion of Universe [duplicate]
Possible Duplicate:
Why space expansion affects matter?
If the Expansion is prevalent, i.e. it is observable and true then shouldn't that result in the expansion of the Milky Way galaxy, ...
1
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1answer
78 views
Two definitions: 'semi-classical space-time' and 'supersymmetric Minkowski space'
By reading articles I ran several times into two terms, never being defined so I assume they must have well established definitions somewhere.
The first is semi-classical space-time. If I where to ...
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0answers
14 views
Expansion of Universe. Will it come to an end? [duplicate]
Possible Duplicate:
Is there a consensus on the fate of our universe?
Its been about 13.7 billion years past the Big Bang took place. According to Hubble's law, the universe is under ...
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0answers
65 views
Is existence timeless or in time? [closed]
What is the nature of existence? When something exists, does it exist for all time, or do things come and go? Or does only the present exist. To quote Wheeler, "The past has no existence except as it ...
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1answer
116 views
A question about multiverse
I have a question that I would like to ask here since I'm not an expert or any near to that.
Actually I just came up with this question when I was watching The fabric of cosmos.
I couldn't find where ...
7
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1answer
261 views
Plotting the CMB power spectrum - Why $C_\ell \ell (\ell+1)$ rather than only $C_\ell$?
I can't find any convincing answer for the following question :
Why do we always (or often) plot the CMB power spectrum in this way?
I mean the y axis is $C_\ell \ell (\ell+1)$ and not only ...
2
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0answers
71 views
Does dark energy affect asymptotic freedom?
If the Hubble constant is extremely large, what will happen with quark confinement?
I guess that quarks will remain confined because of asymptotic freedom. But can gravity or dark energy have any ...
0
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4answers
377 views
Can the big bang be “light turning into space” at the edge of the universe?
The theory I've recently come to postulates that:
The volume of space filling the universe is finite and is constantly growing, thus the boundaries of the universe are constantly expanding.
The ...
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1answer
46 views
observation and implied time since creation
I read on a post
Big Bang and Cosmic microwave background radiation?
We detect light from another 13 billion years ago does this mean that one billion years ago we could only detect light from about ...
2
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1answer
210 views
How is it possible that we see light from shortly after the big bang?
How can astronomers see light from shortly after the big bang? How did we get "here" before the light that emanated from our "creation"?
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0answers
64 views
Temperature of the CMB when the Earth formed and the faint young Sun paradox
The cosmic microwave background (CMB) has a modern temperature of about 2.7 K. At the time of the origin of the CMB, about 13.6 billion years ago, it had a temperature of about 3000 K.
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3
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2answers
416 views
Zero divergence of energy-momentum tensor and gravitational energy
Trying to teach myself general relativity and have just hit yet another confusion. I'm reading that in curved spacetime the energy-momentum tensor has zero divergence, ie
...
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1answer
71 views
If space is being doubled, how fast is it doubling? [duplicate]
Possible Duplicate:
How long does it take for expanding space to double in size
According to the standard concordence model, I heard that it's likely that space is doubled after 11.4 ...
0
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1answer
126 views
Proportion of energy compared to mass in universe
In Wikipedia (http://en.wikipedia.org/wiki/Dark_matter), there is a picture that shows us the proportion of matter and energy in the current universe - CMB.
It seems to suggest there is nothing that ...
4
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2answers
243 views
Does the current acceleration of universe imply that our universe is open?
Does the current acceleration of universe imply that our universe is open?
If the universe is closed, from the Friedmann's equation, the acceleration of universe wouldn't be possible, would it be? (Of ...
7
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1answer
586 views
In what sense does the universe have an outer edge?
I'm having trouble understanding something about Suskind's Holographic principle. Suskind speaks about the surface of the universe? In what sense does the universe have an outer surface? I'm a bit ...
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2answers
206 views
How is Big Bang related to theory of relativity?
I'm not someone with good scientific knowledge, so if my question are weird, correct me.
I was reading about big bang and I came by the theory of relativity. Can someone explain the relation between ...
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1answer
57 views
What would be the effects of an inflating universe?
If our universe is inflating, which means it is getting bigger and bigger in size, and every thing it consists of is also enlarging, in a special way such that the mass of the universe remains ...
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1answer
133 views
If the unobservable universe is not “open” and will collapse, would we be able to tell?
Assuming hypothetically that it happens now while we are alive and analyzing our observable universe. If the unobservable universe collapses in a "Big Crunch", will we see its effects in our ...
4
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1answer
141 views
Do black holes play a role in quantum decoherence?
Sorry for such a vague question but I could have sworn I read somewhere that Hawking proposed the reason we might see a classically appearing universe is due to the possible role of black holes in ...
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1answer
194 views
What allows us to infer the existence of dark energy?
A recent Indian examination asked: how do we infer dark energy is there? It gave as options: rotation curves of galaxies, accelerated expansion of the universe, existence of microwave background ...
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1answer
210 views
spacetime expansion and universe expansion?
First of all, does the expansion of spacetime solely cause the expansion of universe?
Secondly, if spacetime is the sole cause, do objects(matter with mass) themselves expand?
Thirdly, by spacetime ...
1
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1answer
193 views
String theory landscape and false vacua
What is the multiverse of string theory? I always thought it would be from brane cosmology where there's chances for multiple collisions of the branes that can make a universe. So this "multiverse" ...
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0answers
36 views
Baryon asymmetry [duplicate]
Possible Duplicate:
Baryon asymmetry
Baryon asymmetry refers to the observation that apparently there is matter in the Universe but not much antimatter. We don't see galaxies made of ...
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vote
1answer
141 views
Why is Hawking's No Boundary condition described in terms of an instanton if there's no tunneling?
Regarding his take about combining No Boundary proposal with inflation theory (Hawking and Turok), he talks about the "pea instanton".
To my very limited understanding I thought instantons were only ...
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2answers
217 views
Baryon asymmetry
Baryon asymmetry refers to the observation that apparently there is matter in the Universe but not much antimatter. We don't see galaxies made of antimatter or observe gamma rays that would be ...
1
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1answer
129 views
Can someone explain probability flux in the tunneling boundary condition of Vilenkin?
This is what's leading to the notion of a quantum universe tunneling from nothing into existence, right? The idea is that probability flux flows out of superspace (configuration space) at ...
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0answers
171 views
Extrinsic curvature versus Intrinsic curvature (Euclidean versus Riemannian)
Do we believe the universe has any extrinsic curvature at all? As far as I'm aware extrinsic curvature is only used in geometry/math to model the intrinsic curvature, correct?
From the answers to ...
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1answer
206 views
What is the fate of a 3-Torus universe?
Since it is flat, will it expand forever like a flat and open universe or collapse like a closed and curved universe?
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1answer
192 views
Is the FRW metric describing the shape of the universe or the shape of the expansion applied to the universe?
Is it (the output, i.e, spherical, flat, hyperbolic) describing the physical shape of the universe and its curvature at any given instance of time or is it describing the shape of the expansion ...
2
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1answer
232 views
Could the unobservable universe have curvature (be spherical)?
What prevents the unobservable universe from being a continuously enlarging sphere due to the inflating bubble universes? Our observable universe being close to flat could support such a scenario?
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4answers
248 views
Age of universe estimates
I was recently involved in a discussion on a sister site regarding how tightly coupled Physics is with the age of the Universe (and Earth).
I believe that the Earth and the Universe are both billions ...
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1answer
164 views
Why is the universe described in terms of Euclidean space and not Minkowski spacetime?
The universe is described as an infinite Euclidean space in cosmology. Why isn't it treated as Minkowski spacetime?
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1answer
283 views
How did the inflaton field “add” energy to the universe?
How did inflation add energy to the universe? What mechanism did this occur by? In other words, where did that energy come from? Was it due to the quantum fluctuation (or that scalar field rolling ...
3
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2answers
164 views
Why does inflation (the inflaton field) push Omega down closer to zero (flatten the universe)?
I know that in our particular case the inflaton field expanded the volume of the universe while simultaneously maintaining a mass-energy density close to the critical density all the while, thus the ...
