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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3answers
336 views
References for ADM formalism and cosmological perturbation theory [closed]
What would you consider the best online resources for learning the 3+1 ADM formalism and gauge invariant perturbation theory in cosmology? (Assuming intermediate level GR and QFT familiarity)
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1answer
85 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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1answer
885 views
Hubble time, the age of the Universe and expansion rate
The Hubble time is about 14 billion years. The estimated current age of the Universe is about 13.7 billion years. Is the reason these two time are so close (a) a coincidence, or (b) a reflection that ...
2
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1answer
121 views
Fine Tuned Universe
Is the fine tuning that cosmologists talk about (that our Universe is fine tuned for intelligent life) is the same as the fine tuning of the squared mass parameter of the Higgs in the Standard Model? ...
2
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2answers
167 views
Can the implications of dark energy be used to bridge the gap between Quantum Mechanics and General Relativity?
Can the findings of the Physics Nobel Laureates of 2011, namely the overpowering existence of dark energy (vacuum energy) have any implications in the quest the combine Quantum Mechanics and General ...
2
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3answers
211 views
Distance in cosmology
How can we calculate the change in distance over time between (say) two galaxies that they are at rest in respect to each other?
In other words, how do we modify the "classical" equation:
$$ ...
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4answers
883 views
Maximum size of the observable universe?
The size of our observable universe must have grown over time in the early universe. Conversely with the accelerated expansion, I have heard that eventually our observable universe will shrink down ...
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1answer
98 views
Ricci scalars for space and spacetime, local and global curvature
If Ricci scalar describes the full spacetime curvature, then what do we mean by $k=0,+1,-1$ being flat, positive and negative curved space?
Is $k$ special version of a constant "3d-Ricci" scalar?
...
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0answers
46 views
Is the speed of light the ultimate speed limit? [duplicate]
As we all know nothing can go faster than the speed of light as mentioned by most of our pioneer's in physics. But as I was listening to one of the statements of Sir. Stephen Hawkins he stated that at ...
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2answers
75 views
Distance of universe's most distant objects in relation to expansion of the universe
Was reading this article about the Hubble XDF and it had the quote:
The most distant objects here are over 13 billion light years away, and we see them when they were only 500 million years old.
...
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2answers
196 views
Dark matter and dark energy [duplicate]
Possible Duplicate:
Dark matter references
I have recently read about dark matter and dark energy, and why physicists think it must exist (dark matter: mass of galaxies are far bigger than ...
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vote
4answers
424 views
Why can't missing mass be photons?
After a star lives and dies, I assume virtually all of it's mass would be photons. If enough stars have already lived and died, couldn't there be enough photon energy out there to account for all the ...
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1answer
180 views
Do atoms expand with universe? [duplicate]
Possible Duplicate:
Why space expansion affects matter?
Why does space expansion not expand matter?
As we know, the universe is expanding, galaxies are away from each other. But what ...
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3answers
156 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?
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1answer
131 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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vote
1answer
159 views
Are there any theories or suggestions for how the multiverse came into existence?
I've just seen a documentary about the multiverse. This provides an explanation for where the big bang came from. But it leaves me wondering: how did the multiverse come into existence?
Because this ...
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0answers
55 views
How is it possible to measure expansion of universe [duplicate]
Possible Duplicate:
Why does space expansion not expand matter?
If according to Hubble's law space the expanding then shouldn't everything else along with the space expand and we should not ...
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0answers
214 views
Presence Of an Another Universe [duplicate]
Possible Duplicate:
Experimental evidence for parallel universes
Is there an universe similar to ours somewhere else, I mean I had heard from Einsteins theories that,actually when I am ...
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1answer
442 views
Has Cosmological Natural Selection been disproved?
I've been reading Lee Smolin's Life of the Cosmos.
Great book and it makes a lot of sense that the conditions in black holes are the same as conditions at the big bang.
Question is, has his theory ...
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2answers
361 views
Expansion of the space-time metric
If the space-time metric is expanding with the expansion of the universe, if I could travel back in time, would I be less dense than the matter in that previous era?
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1answer
376 views
How to calculate the density of relic neutrinos?
May be not neutrinos, but antineutrinos? Or both types?
In the last case, why they didn't annihilate and what is the ratio of relic neutrinos to relic antineutrinos? Is that ratio somehow related to ...
1
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0answers
138 views
Why is “dark matter” a more parsimonious explanation than “more normal matter than we thought”? [duplicate]
Possible Duplicate:
Why isn't dark matter just matter ?
The evidence usually presented in support of dark matter is larger-than-expected masses in galaxy clusters: the mass required for ...
0
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3answers
118 views
Cosmological redshift interpretation
Can the cosmological redshift be interpreted as atomic frequencies increasing by the scale factor as the Universe expands?
This explanation seems closer to the truth than the popular idea that a ...
0
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1answer
148 views
Did space and time exist before the Big Bang? [duplicate]
I accept the Big Bang theory. What I can't understand is how there can be a where or when to the Big Bang if space time did not exist prior to it. Did space and time exist prior to the Big Bang?
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1answer
82 views
Speed of Universe Expansion [duplicate]
How much is the universe expanding every second (Earth second)?
If you could be a bit simple in the answer that would be good.
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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 ...
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2answers
145 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?
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1answer
304 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 ...
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2answers
290 views
Does the Big Bang need a cause? [duplicate]
Possible Duplicate:
on causality and The Big Bang Theory
Asking here in layman's terms..
When theoretical physicsists discuss the origin of our Universe, the wider consensus appears to be ...
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1answer
259 views
Inflation factor and doubling time
I get the general idea about cosmic inflation, but the numbers associated with it seem to be pulled out at random.
For example, in The Elegant Universe, Brian Greene says that the universe doubled ...
0
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2answers
219 views
Have CMB photons “cooled” or been “stretched”?
Introductory texts and popular accounts of why we see the "once hot" CMB as microwaves nearly always say something about the photons "cooling" since the Big Bang. But isn't that misleading? Don't ...
-3
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1answer
278 views
Is antigravity the source of accelerating expansion (dark energy)?
Is antigravity the source of accelerating expansion(dark energy)?
From the observation of 1998, we found that our universe has been continuing accelerating expansion, and the unknown cause for this ...
