Cosmological inflation refers to an era of expansion that lasted for approximately $10^{-34}$ seconds, during which the universe expanded by a factor of approximately $10^26$ in every direction. This is different from ordinary space expansion and from the acceleration in expansion we experience now ...

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How do we know that space expanded with speed faster that a speed of light during big-bang inflation?

How do we know that space expanded faster than a speed of light in inflation? I have read this Phys.SE question, and it says that limit for faster than a speed of light is for matter and waves only. I ...
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158 views

Is the Big Bang defined as before or after Inflation?

Is the Big Bang defined as before or after Inflation? Seems like a simple enough question to answer right? And if just yesterday I were to encounter this, I'd have given a definite answer. But I've ...
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1answer
31 views

Negative Energy in Inflation Theory (Low/Zero Energy Universe)

I've been reading Max Tegmark's book: Our Mathematical Universe. It's very interesting, but I wanted to know more about one particular thing. The book simplifies things and I know inflation theories ...
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4answers
62 views

Why doesn't the light from galaxies appear stretched? [duplicate]

Maybe it's my ignorance of astrophysics/cosmology, but I have been wondering this: Why do galaxies not appear stretched when we observe them? Assuming a galaxy that we observe is 100,000 light years ...
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Why the initial spectrum of perturbation of inflation must be Gaussian?

Why the initial spectrum of perturbation of inflation must be Gaussian? I heared it was because of Central Limit theorem. But I don't know how use this theorem explicitly in this question to get this ...
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35 views

What's the difference between correlation functions and S-matrix, and between in-in formalism (or “closed time path formalism”) and in-out formalism?

I was reading the "in-in" formalism (or "closed time path formalism" used in condensed matter physics) in cosmology created by Schwinger in 1961, and there is a saying: "they care about correlation ...
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1answer
91 views

How did the universe get so big so fast? [duplicate]

The universe started at the big bang around 15 billion years ago. The universe is now at least 92 billion light-years in diameter. Together, don't these mean that the universe, at some time in the ...
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93 views

Does expanding space cost energy?

Does the cosmic inflation reduce the energy density (inversely) proportional to the volume, or does the inflation "cost" energy? Is space itself "something" created at the expense of energy?
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1answer
47 views

Number of Stars vs Value of Omega (Crtitical Density of the Universe)

I may be badly mixing things up here. If I am, please kindly correct me. As I understand it, if the universe was too dense at the start of the big bang, it would have collapsed back in on itself. Too ...
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26 views

How do inflationary models predict the generation of gravitational waves during the inflationary period?

Recent results from the BICEP2 experiment have produced a lot of talk about the primordial gravitational waves produced during the inflationary period. I would like to have some explanation about how ...
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1answer
32 views

Attractive higgs force and inflation

Inflation was the extreme accelerating expansion of the universe, see here: http://en.wikipedia.org/wiki/Inflation_(cosmology) It worked in a similar way to dark energy but was so strong it would ...
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32 views

Is the expansion accelerating or decelerating? [duplicate]

I have already asked this on Astronomy.SE but I couldn't understand the answer there. According to Hubble's Law, the farther a galaxy is, the farther it is moving away. But do we take into account ...
2
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1answer
31 views

Sign of Hubble slow-roll parameters

Given the Hubble slow-roll parameters $\epsilon=-\frac{\dot{H}}{H^{2}}$ and $\eta=\frac{\dot{\epsilon}}{H\epsilon}$, can they assume negative values? For inflation to occurr they are required to be ...
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34 views

Units and missing constants in quintessence expressions?

In cosmology, quintessence is an alternative to the cosmological constant. In this approach (described here), we consider a scalar field $\phi$ and its self-interacting potential $V\left(\phi\right)$ ...
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0answers
85 views

Why did everything in space cooled out?

Through my research, I learned that; According to thermophysics, heat always moves from and area of high heat to an area of low heat. Space has no heat at all. It is extremely cold However, ...
2
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0answers
53 views

The speed of light during the inflationary period

Introduction: As a thought experiment, suppose I modified the value of $c$ (speed of light) in some local region and attempted to measure it with a clock placed in that same region. I will denote ...
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2answers
260 views

gravitational waves and inflation theory

I am not a technical guy and I have no scientific knowloedge in physics but I have been reading books, watching videos in order to understand our cosmology and ...
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2answers
82 views

Entropy was created after inflation?

I'm puzzeled by a statement in Big Bang Cosmology-review about the reheating phase subsequent to the exponential expansion during inflation: In this reheating process, entropy has been created ...
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What is chaotic about Chaotic Inflation?

Chaos is defined as an aperiodic long-termed behavior, that is very sensitive to initial conditions. Now from this definition I can only conclude that the adjective 'chaos' is a mere analogy, since ...
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Are black holes trapdoors to the center of the universe? [closed]

Correct me if i'm wrong here, but if you consider the analogy of inflating balloon when explaining the universe expansion, then the center of the universe lies within the center of the inflating ...
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150 views

the nature of the big bang

If space-time expanded together with matter then why do physicist bother extrapolating backwards the expansion back to a point in time? I mean does that really tell us anything? I mean if the speed of ...
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0answers
54 views

What does it mean to have infinite negative conformal time?

In the context of Inflationary Cosmology, it is postulated that there was a period of shrinking Hubble Sphere radius $(aH)^{-1}$. $$ \frac{d}{dt} (aH)^{-1} < 0 $$ Then the regions of the ...
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1answer
40 views

Primordial flunctuation gave rise to cosmic structures?

I'm not a physicist, not even a physics student. I'm just reading Lawrence Krauss's book A Universe From Nothing and I got stuck understanding a concept. In his book, Lawrence says: Quantum ...
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1answer
59 views

In a universe that is expanding at a constant rate, do objects that are attracted to each other feel a force opposite to their attraction?

In this article, the authors make the claim (pg 44) that "Expansion by itself—that is, a coasting expansion neither accelerating nor decelerating—produces no force." I'm having a hard time convincing ...
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1answer
78 views

Deriving the slow-roll parameter $\eta$

In inflationary theory, many papers start off by making the slow-roll approximation, on which many things depend. This approximation is usually presented by requiring that two 'slow-roll parameters' ...
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1answer
73 views

Universe inflation [duplicate]

Read in several publications that the Universe during a very short time (inflation), increased its size by a factor of $10^{50}$. What does it mean to increase the size of $10^{50}$ if you do not ...
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174 views

Cosmological constant doubts

I have read about cosmological constant given by einstein in universe in nutshell as well as in general and special relativity. But still I am not able to understand the aim to use it or to introduce ...
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0answers
25 views

Question on Equipartition at Reheating?

Apologies in advance if this is a silly question. I am fimiliar with the idea of Reheating in cosmology, as discussed briefly here. I have been reading several papers which make the assumption of ...
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111 views

Understanding Bose enhancement in reheating

I'm struggling to understand the Bose enhancement in reheating. I've read that: At the end of inflation, the inflaton field, $\phi$, is something like a condensate with excitations of a single ...
3
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1answer
59 views

'There shall be reheating' and other inflation-related questions [closed]

I've some basic questions about inflation: What is reheating exactly? What triggered the reheating? Is it something that one pulls out of a hat? Through which force did the decay of the inflation ...
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3answers
149 views

Is the universe flat?

There are more than one way to view the description of the universe as flat. There is the description of an open, flat or closed universe in terms of it's fate, expansion forever away from gravity, or ...
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1answer
148 views

Does Lyapunov exponent equate to exponential inflation?

Physics can be modeled by dynamical systems $f^t(x)$ as well as by PDEs. The most common dynamical system has hyperbolic fixed point and can be an attractor or a repellor. The dynamics at repellors ...
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1answer
70 views

Is redshift the only way by which we can tell that space is expanding?

There's another question on physics.SE whose answer, if I have understood it correctly, explains that the farther the points are in space the faster they are moving away from each other. Actually, ...
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1answer
85 views

Inflation in a closed universe or a stage 1 multiverse?

With the discovery of gravitational waves, Max Tegmark has been using this to promote his level 1 multiverse in that the universe is open (non-compact) and everything duplicates. My question is, are ...
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1answer
102 views

Is the Universe Past-Eternal?

Does the Borde-Guth-Vilenkin theorem definitively demonstrate that the Universe cannot be past-eternal, whatsoever? Does it not assume a classical space-time while the real world requires Quantum ...
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1answer
94 views

Does inflation predict a multiverse?

Does inflation necessarily predict a multiverse? Or is it the case that "It all depends on the properties of the initial field responsible for inflation, about which we can only speculate"?
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1answer
59 views

What is the mass of the universe?

Working with a flat and infinite model of the universe (which seems to be the most popular serious model these days), the density of the universe is 3e-28 kg/m^3 [1]. When added to the cosmological ...
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Inflation and the Meaning of Time

I'm not quite sure how to ask this so that it can be answered in layman's terms, but I have lately seen, in several places, that with cosmological inflation, there was a point where the universe ...
3
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1answer
74 views

What is $\phi$ as refered to in Guth 2007?

In this 2007 paper by Alan Guth discussing eternal cosmic inflation, he start's using a value $\phi$ on page 8. My understanding is that $\phi$ is the scalar field representing the dark energy of a ...
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1answer
84 views

The gravity waves from the big bang? How can we know?

The latest news says that scientists detected gravitational waves from the Big Bang. My question is how do they know the waves originated in the big bang verses any number of supernovae and or ...
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1answer
127 views

In the B mode power spectrum, what is the relationship between the multipole number and the wavelength of the seed gravitational waves?

One of the key datasets of the recent BICEP2 results is the B mode power spectrum shown below. The existence of these B modes implies the existence of gravitational waves prior to inflation. My ...
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1answer
168 views

Is the interpretation of BICEP2 data being due to “graviational waves” concerning considering the negative results of the LIGO's experiments? [closed]

Gravitational waves are a yet unproven idea... The lack of positive results from LIGO indicates these are still theoretical constructs not yet supported by experimental data. Is not the explanation of ...
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2answers
107 views

Size of Universe after inflation

I read in some website that during the period of inflation, the expansion of the universe underwent incredibly fast, and its size increased by a factor of $10 ^{50}$, see this link In this field, I ...
7
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1answer
226 views

The BICEP2 data are evidence of gravitational waves and of inflation. Are they also the first observation that requires quantum gravity?

It strikes me that the recent announcement of data from BICEP2 contains two really Big Deals: the first evidence of gravitational waves the first evidence of inflation. Is there also a third? ...
10
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1answer
163 views

What's the $\ell$ in the Bicep2 paper mean?

The BICEP experiment's recent announcement included the preprint of their paper, BICEP2 I: Detection of $B$-mode polarization at degree angular scales. BICEP2 Collaboration. To be submitted. ...
3
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1answer
141 views

How big of an area of the sky is the BICEP2 survey?

So here is the BICEP2 picture: How big is that? How much of the sky? Say, compared to this picture of the CMB by Planck:
3
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1answer
176 views

What is the minisuperspace Lagrangian for gravity plus a scalar field?

In this paper by Sean Carroll and Grant Remmen, in equation (11) they write a Lagrangian of the form $$\boxed{\mathcal{L}=3a\left(k-\dot{a}^2\right)+a^3\left[\frac{1}{2}\dot\phi^2-V(\phi)\right]}$$ ...
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1answer
40 views

Is Λ-CDM and no inflaton field compatible with the observed value of the scalar spectral index?

From the cosmic microwave background, one can extract the scalar spectral index $n_s$. It is measured to be smaller than 1 by several standard deviations. Wikipedia says that it is a parameter of the ...
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320 views

BICEP2 and string theory

Can anybody elaborate on the implications of the BICEP2 result for string theory? The discussion here What experiment would disprove string theory? suggests that refuting string theory is rather ...
9
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1answer
162 views

BICEP2 and e-foldings during inflation

After the BICEP2 results, we now know that $n_s = 0.96$ and $r = 0.2$. From what I understand, this fits extremely well with the basic chaotic inflation model given by $V(\Phi) = \lambda \Phi^4$. We ...