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5
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2answers
587 views

Planck satellite 2013 results impact on cosmological models

I've recently watched a "Through the Wormhole" episode from 2010 named "What Happened Before the Beginning?", where cyclic and ekpyrotic cosmological models are explained. In this episode the creators ...
2
votes
2answers
131 views

How can bubble universes collide in eternal inflation?

In eternal inflation, how can bubble universes collide if the space between them is exponentially stretching and moving them further and further away?
5
votes
3answers
287 views

What does string theory say about the metric expansion?

Specifically, what happens to those small intertwined hidden dimensions? Do those expand too?
3
votes
3answers
161 views

What would be the effect on gravity if space expanded at > $c$?

If space were to expand at > $c$ (as in inflation) would that mean gravity would no longer have any effect on the curvature of space, since gravity can only propagate at $c$?
1
vote
3answers
383 views

Entropy and Big Bang aren't mutually exclusible? [closed]

There are some principles in entropy im having trouble understanding. If Entropy requires that the energy in the universe must always been constant, shouldnt in theory 'Heat Death' have occurred since ...
4
votes
1answer
453 views

Additional merits to Wetterich's “Universe without expansion” compared to standard cosmological redshift interpretation?

A recent news item in Nature promotes Wetterich's preprint "A Universe without expansion". All sounds very exciting but hard to judge for non-experts. As I understand from the Nature's article, the ...
4
votes
1answer
98 views

How can contracting dimensions lead to cosmological inflation?

Using the Kasner metric, given by $$ ds^2 = -dt^2 + \sum_{j=1}^D t^{2p_j}(dx^j) $$ it is possible to not only describe the cosmological expansion of some space directions (the ones with positive ...
13
votes
0answers
228 views

Before inflation, what sets the initial value of the inflaton field?

[This is a version of the question that I've revised based on helpful comments from Dan.] I haven't studied inflation at a technical level. My picture of the process is that we have an inflaton field ...
0
votes
2answers
74 views

Spread and direction of the cosmic background radiation

Something I can never understand is that where the cosmic background radiation spreads? If I know well, the cosmic background radiation is actually the light of the Big Bang. If it happened exactly ...
6
votes
1answer
118 views

Causal structure of the inflationary multiverse

In the multiverse as it is described by eternal inflation, it is not clear to me what is its causal structure and in particular if the bubble-universes are causally connected. We start from a ...
2
votes
0answers
110 views

Cosmic Inflation: Lower Expansion Rate with than without?

When I read the Cosmic Inflation diagram at https://en.wikipedia.org/wiki/File:Horizonte_inflacionario.svg which I rotated to make it readable: where the Hubbleradius, and therefore also the ...
0
votes
3answers
148 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?
6
votes
0answers
110 views

How can dynamics be reversible if inflation-style baby universe spawning is allowed?

I just finished readying Sean Carroll's book, "From Eternity to Here", and have a question about reversibility and inflation: Assume inflation allows random quantum fluctuations to produce high ...
1
vote
2answers
253 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.
4
votes
1answer
353 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
66 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
196 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 ...
7
votes
0answers
51 views

Hybrid Inflation and Supergravity

Is it necessary to add a constant term in the superpotential of hybrid inflation within supergravity in order to cancel SUSY vacuum energy at the end of inflation?
4
votes
0answers
207 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 ...
2
votes
0answers
47 views

Is Inflation modelled by a field?

If Inflation is modelled by a field - is this a classical field or a quantum field? If classical are there good reasons not to quantise it? What are the implications of such a quantisation?
1
vote
1answer
36 views

Is the redshift of ancient stars less than constant linear expansion predicts?

When accelerated expansion of universe was discovered, the astronomers used redshift of ancient stars. Say if star is 10 billion years in the past, then it should be moving faster than star from 5 ...
1
vote
0answers
56 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 ...
5
votes
0answers
69 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" ...
4
votes
3answers
336 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
207 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
votes
1answer
774 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
112 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
489 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 ...
3
votes
1answer
110 views

false vacuum original paper

I'm trying to track down the origin of the False Vacuum paradigm. Is it Coleman and de Luccia's "Gravitational Effects on and of Vacuum Decay" ...
2
votes
0answers
98 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
209 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
94 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 ...
8
votes
3answers
781 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 ...
9
votes
4answers
4k 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
234 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
77 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
302 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
vote
1answer
278 views

How fast was the universe expanding during the inflationary period?

Compared to how fast it is expanding in the post-inflationary period (now)
4
votes
2answers
656 views

The multiverse of eternal inflation

I don't have a clear picture of what is "by definition" the multiverse appearing in the models of eternal inflation. A long time ago I heard that it is a quantum state, but in the cosmology books I ...
0
votes
1answer
84 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
229 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
255 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" ...
2
votes
1answer
196 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
230 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
290 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
651 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
278 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 ...
3
votes
1answer
247 views

Curvature, Omega, the Flatness problem, and the evolving shape of the universe

I'm a little confused by this: http://en.wikipedia.org/wiki/Flatness_problem Which seems to imply the universe is more curved now than it was soon after the Big Bang. Look at the graph on the right ...
1
vote
1answer
425 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
244 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 ...