Tagged Questions
0
votes
3answers
80 views
Acceleration in the rate of expanansion of the universe due to weakening gravity?
Could the acceleration in the rate of expansion of the universe be due to the weakening of gravitational forces, as the distance between objects continues to increase?
1
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2answers
82 views
What is the speed of acceleration of the inflation of the universe?
Is the inflation speed of the universe accelerating or is it a constant speed of expansion proportional to distance between objects.
2
votes
1answer
89 views
Inflation and scalar spectral index
I've been reading that the results from the Planck satellite constrain a number called the "scalar spectral index" to be 0.96 rather than 1 at the 5-sigma level.
This is supposed to be big news, but ...
2
votes
1answer
57 views
Tensor perturbation inflation
During inflation the metric is de-Sitter so $dt^2-d\underline{X}^2 $.
I know that the eqn.motion governing GW's from inflation (tensor perturbations) is
$$2H\dot{h}+\ddot{h}-\nabla^{2}_{i}h~=~0,$$ ...
2
votes
1answer
107 views
Observable (in principle) signal of a bubble collision in eternal inflation
Assuming a scenario of eternal inflation with a lot of "bubble universes" expanding, Lenny Susskind explains here that a potential signal of a collision of our universe with another bubble could be a ...
3
votes
0answers
147 views
Quantum Entanglement Versus Inflation in the Early Universe?
Quantum entanglement is one of the most fascinating and mysterious phenomena in nature. It needs no interactions, or any sort of exchange for it to take place. It is possible, not against any rules of ...
1
vote
0answers
41 views
The definition of $f_{NL}$ and transfer function
To me there seems to be quite a few different definitions of $f_{NL}$ in cosmology and I would like to know if or how they are equivalent. Let me cite at least 3 such,
One can see the equation 6.71 ...
4
votes
0answers
49 views
$f_{NL}$ non-Gaussianity in cosmology
In the context of cosmology, what is meant by "..arbitrary quadratic non-Gaussianity i.e non-Gaussianity that is described to leading order by a 3-point function.."? (.."quadratic non-Gaussianity" ...
3
votes
3answers
220 views
Question on inflation
I have two particular questions regarding the inflationary scenario. They are:
1.) What is the physical origin of the inflaton field?
2.) Why has the potential of the inflation field its particular ...
3
votes
1answer
121 views
Question on inflation as a phase transition
I have just finished watching the following video http://www.youtube.com/watch?v=beQ9fZ0jVdE where Laughlin, Gross and some students discuss e.g. about inflation. The following question is risen:
Is ...
0
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0answers
90 views
Theoretical early-universe cosmology [closed]
I wanted to know what are the cutting edge/recent papers to read w.r.t theoretical early universe cosmology.
I would like to know of recent review papers
I would like to know of areas which use ...
0
votes
1answer
295 views
How does an inflationary universe solve the Flatness Problem, Horizon Problem and Monopole Problem? [duplicate]
Possible Duplicate:
What is the evidence for Inflation of the early universe?
I am reading some public science books on inflationary universe, e.g. The Inflationary Universe by A. Guth.
...
2
votes
0answers
83 views
Can decompactification explain the inflation of the early universe?
I've just reread chapter 11 of this book where it is explained among other things, that our four dimensional universe could be unstable concerning a decompactification transition, since potential ...
5
votes
3answers
207 views
Why the red-shift of distant galaxies is considered to be the effect of expanding spacetime?
Why it's not explained just by Doppler redshift caused by faster movement of those galaxies billions of years ago when that light was emitted?
Would the speeds of the galaxies necessary for Doppler ...
2
votes
0answers
73 views
Is it really true that slow-roll inflation is incompatible with string theory?
In this blog post, Motl claimed that slow-roll inflation is incompatible with string theory. Is that really true, and why do people think so?
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 ...
2
votes
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 ...
5
votes
3answers
374 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 ...
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. ...
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 ...
0
votes
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
votes
2answers
180 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 ...
0
votes
1answer
56 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 ...
0
votes
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 ...
1
vote
1answer
191 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" ...
1
vote
1answer
140 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 ...
0
votes
1answer
188 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
votes
1answer
231 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?
0
votes
1answer
278 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
votes
2answers
163 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 ...
1
vote
1answer
302 views
How did the energy/entropy/volume/pressure/temperature relationship exist at the Big Bang and how did it evolve thereafter?
According to the current Big Bang with inflation cosmological model?
I was under the mistaken impression that there was very low volume, very high temperature/pressure, very low entropy and the Big ...
5
votes
2answers
112 views
Why does the homogeneity of the universe require inflation?
They say inflation must have occured because the universe is very homogeneous. Otherwise, how could one part of the universe reach the same temperature as another when the distance between the parts ...
1
vote
2answers
190 views
How to concile flat spacetime and big bang?
After reading How do we resolve a flat spacetime and the cosmological principle? I still remain perplex.
Please excuse my ignorance and try explaining to me :
I thought that basically, when we ...
2
votes
2answers
158 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 ...
9
votes
2answers
211 views
How is causal patch complementarity compatible with behavior during inflation?
Causal patch complementarity is the conjecture that in de Sitter space with a positive cosmological constant, the states within the causal patch are sufficient to fully describe the universe with the ...
8
votes
2answers
357 views
Is eternal inflation and the multiverse compatible with causal patch complementarity?
The argument for eternal inflation is we have some patch of metastable vacuum with positive cosmological constant, and so it expands exponentially a la de Sitter. Most of the patch decays to something ...
2
votes
1answer
41 views
Cosmic bubble collision
I'm reading this review right now. The claim seems to be that when you have an expanding "false vacuum", finite size bubbles form due to phase transition (cause by finite action instantons) (which, in ...
1
vote
2answers
286 views
How long did inflation take to happen?
If inflation happened, it ended about 13.7 billion years ago. But how long was inflation going on before that? Was it just a short burst of time so that it's really okay to say that the age of the ...
2
votes
1answer
145 views
Does anisotropic expansion of the universe imply quintaessence?
a Recent paper establishes under solid grounds anisotropy in the expansion acceleration rate in the universe. My question is very simple:
can this anomaly be explained entirely in terms of a ...
5
votes
2answers
383 views
photons in expanding space: how is energy conserved?
If a photon (wave package) redshifts (streches) traveling in our expanding universe, is it's energy reduced? If so, where does it go?
-3
votes
2answers
143 views
Could dark matter be expanded atoms, and dark energy expanded radiation?
After watching Lawrence Krauss' lecture 'life, universe, and nothing', an interesting idea lighted up in my mind. Is it possible that dark matter is just spread out matter waves and dark energy ...
0
votes
1answer
247 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 ...
10
votes
2answers
425 views
Can “big rip” rip apart an atomic nucleus?
Some scenarios describing the fate of the matter vs dark energy tug of war on the universe involve the acceleration of the universe increasing to the point that it ends up ripping apart even atoms. ...
1
vote
1answer
220 views
Inflation and string theory in general relativity
How can we relate inflation and string theory? We study some inflationary cosmological model or some string cosmological model under some specific assumptions or conditions.
Is their any relation or ...
6
votes
4answers
450 views
de sitter cosmologic limit
It has been said that our universe is going to eventually become a de sitter universe. Expansion will accelerate until their relative speed become higher than the speed of light.
So i want to ...
2
votes
1answer
161 views
Size of our inflationary bubble
Once again, an attempt to connect popular and real science.
I have read that inflation implies our universe should look flat, or really close to flat, because our observable universe is only a really ...
4
votes
2answers
344 views
Undergraduate-friendly reading material on the multiverse?
I'll be teaching a seminar for first-year undergraduates next year. The idea of my university's first-year seminar program is to expose students to exciting ideas and important texts in a somewhat ...
5
votes
5answers
2k views
What is the evidence for Inflation of the early universe?
The theory of Inflation explains the apparent consistency of the universe by proposing that the early universe grew exponentially for a 1E-36 seconds. Isn't a simpler explanation that the universe is ...
4
votes
3answers
302 views
What current alternatives are there to the standard concordance model of cosmology?
The current "standard model" or concordance model of cosmology is Lambda CDM which includes late time acceleration due to a cosmological constant, cold dark matter as the missing matter component and ...
