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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Conformal Gravity

Lubos, in his comment to a question, says that (http://physics.stackexchange.com/q/61281) First of all, one can't gauge a symmetry without modifying (enriching) the field contents. Gauging a ...
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210 views

Big Freeze or Heat Death?

I can't seem to find this on the Internet.... Which is most likely to occur to "end" the universe, the big freeze scenario? Or the heat death scenario? P.s. When, if it does at all, will the ...
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279 views

What is meant by the term “value” of a scalar quantum field?

During the slow roll of a scalar field, the scalar field is changing its value over time. But what is meant by the term "value" of a scalar field? Since the scalar field is quantized, I don't ...
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How to understand that Inflation generate almost scale-invariant perturbations?

Since during the inflation, the Hubble rate is approximately constant, the perturbations generated by inflation are almost scale-invariant. How to understand that?
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Slow-Roll: What is the energy of a scalar field transformed to due to Hubble friction?

So, I've lately been reading about the Slow-Roll approximation of scalar fields. However - since I don't really know that much about cosmology - I have some trouble regarding the understanding of the ...
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Going to the Einstein frame in f(R) theories

First of all thank you for your time! I have a question that I can't solve. In every review that I read, I find that when you want to go to the Einstein frame in a $f(R)$ theory what you have to do ...
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Inflation slow role potential $V=\frac12 m^2{\phi}^2$ [closed]

Consider a slow roll inflation potential $V(\phi)=\frac{1}{2} m^2 \phi^²$. Inflation begins right at the Planck scale with $\phi\sim M_{P}^4$. We want to show $\phi=\phi_{0}-\beta t,$ and get an ...
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162 views

The CMB and the Hubble comoving radius

I have been thinking on this for a while and i don't get it. My point is, the comoving Hubble radius $(aH)^{-1}$ is the distance at wich the universe expansion begins to be superluminical. In an ...
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51 views

Why does the flatness problem (of the universe) present a fine tuning problem?

The Friedmann equation can be written $$|\Omega-1|=\frac{|k|}{a^2H^2}$$ In a period where the universe is decelerated $a^2H^2$ becomes bigger as we extrapolate into the past. We know $|\Omega-1|$ ...
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59 views

How inflation solves the horizon problem

This is a little embarrassing but I don't understand how the inflation model solves the horizon problem. My doubt is the following: What does the occurrence of an exponential expansion of the early ...
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How are the particles produced at the very early universe?

We know that according the standard model of cosmology $\Lambda {\rm CDM}$, there is a primordial plasma after the inflation. And then we study the non-equilibrium evolution of this plasma such as ...
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136 views

Can we embed 2+1 space-time of GR in a 4 Dimensional Euclidean space? [closed]

Wikipedia says that inflation is the exponential expansion of space in the early universe.I'm trying to have a physical picture of this.Given that I can't visualize 3+1 pseudoriemannian manifolds,I'm ...
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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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59 views

Cosmic inflation and space flatness

I am new here, an avid Physics reader, but have lots of questions and doubts on which I'd like to get the help of a pro physicist. Here goes some about the theory of Inflation: a) after the first ...
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757 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 ...
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Exponentially accelerating universe, dark energy, the universe's temperature and event horizons.. (sorry in advance!)

Ok.. assume that space-time is accelerating away from itself with a>0 and.. jerk - j⃗ (t)>0 (sorry - don't know how to write "a dot"! :s ).. If this continues on without the rate of acceleration ever ...
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69 views

What is a slow-roll field?

I am studying inflation reading this article http://lanl.arxiv.org/abs/hep-ph/0406191 and in section 3 it states: This inflaton field may evolve slowly down its effective potential, or not. While ...
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61 views

In a static bounded universe, what happens to particles that hit the edge?

Consider a flat universe. The metric tensor is $$g_{\mu\nu}=\left(\begin{array}{cccc}-1 & 0 & 0 & 0 \\ 0 & 1 & 0 & 0 \\ 0 & 0 & 1 & 0 \\ 0 & 0 & 0 & ...
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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.
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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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264 views

Could the same symmetry be finetuning both the Higgs mass and the inflaton's interactions?

The observed Higgs boson mass is at an interesting place in parameter space, placing the standard model electroweak vacuum right at the edge of metastability. Among the proposed explanations of this ...
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49 views

When did the universe become lighter than water at 1 g/cm3 [closed]

Did the universe become lighter than water before light could travel through it? What temperature was it at the time where matter was roughly 1g/cm3?
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Are there a catalog for various potentials used in inflaton theory, or string theory, or inflation?

The question is if there exist a catalog of various field potentials (one field, two-field, and multi-field) in the literature and the corresponding effects in field theory? I know that the question ...
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60 views

What are the pieces of evidence that universe is expanding? [duplicate]

Do we have any other evidence other than red shift? Is anyone trying to disapprove inflation? Also, can red shift occur because of large distance, not only because two objects are going farther from ...
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28 views

Why must SUSY be broken in SUGRA inflation?

Why must supersymmetry be broken during the inflation in supergravity models? How does adding supersymmetry to power-law or Starobinsky models spoil inflation? And is breaking of SUSY needed for ...
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381 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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32 views

Number of e-foldings in cosmological inflationary theory

It seems that in a lot of lecture courses and notes, including mine and those online, seem to state that the number of e-foldings required is of the order of 50-60. Perhaps I'm looking in the wrong ...
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97 views

Should Anti de Sitter Universe collapse exponentially? (n0)

The de Sitter Universe is described by the Friedmann equation with $k=0$, $\rho=0$ and a positive cosmological constant $\Lambda$: $$\Big(\frac{\dot{a}}{a}\Big)^2=\frac{\Lambda c^2}{3}$$ The ...
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Initial value dependence of slow-roll inflation

Observables in single field slow-roll inflation (lets assume a monomial potential for simplicity) depend only on the number of e-folds at the pivot-scale, $n_s=1-2/N_*$, $r=8/N_*$ etc. On the other ...
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48 views

What are the roles of pre-heating and re-heating in inflation?

During inflation, the universe is thought to have cooled by a "factor of 100,000 or so" The abstract of this paper mentions 'preheating' as playing a role in particle production. Is this 'preheating' ...
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52 views

Slow-roll approximation for potential $V=\frac{1}{2}m^{2}\varphi^{2}$

I'm attempting to derive a solution to the slow-roll approximation for a scalar potential of the form $V=\frac{1}{2}m^{2}\varphi^{2}$. For the solution for $a(t)$ I will start by taking the slow-roll ...
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How is the universe flat?

I have real trouble visualising what is meant by the descriptor 'flat' when referred to the shape of the observable universe. Which one of the below is more accurate? a) It is flat in a 2D way, like ...
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Why relativity doesn't rule out Inflation theory? [duplicate]

Nothing can go faster than the speed of light, then how at the time of inflation space expanded faster than the speed of light? Clearly universe had already begun at the start (10−36 seconds) of ...
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Scales In Inflationary Cosmology

In inflationary cosmology terminologies, what do the scale, scale invariance and scale dependence really mean? This is an excerpt from http://arxiv.org/pdf/astro-ph/0702170v3.pdf "In presenting ...
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Did the universe have a temperature during inflation?

I've heard it said that inflation was not an equilibrium process. But I've also heard it said that during inflation, the temperature of the universe was much cooler than before or after. If the ...
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Is it accurate to say that nothing can travel faster than $c$ in a GR context, where more space can be created?

Years ago, my brother and I had an argument where I was trying to convince him that nothing could travel faster than the speed of light. I was pursuing this in the context of Special Relativity. My ...
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BICEP2 experiments

How was the polarization experimentally measured in the BICEP2 experiments and why did they look specifically at B-modes? Why is it implying the existence of gravitational waves and the need to ...
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544 views

Inflation Scale via CMB Polarization

COBE, WMAP, and now PLANCK, have or are in the process of measuring anisotropies in the cosmic microwave background. WMAP has dectected E-mode polarization from electron Thomson scattering, but not ...
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Problem with denoising BICEP2 data?

This question pertains to this article which talks about why the BICEP2 measurements of B-mode polarization in Cosmic microwave background radiation turned out to be noise from galactic stardust. They ...
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41 views

Did the strong force trigger inflation?

I understand there can only be speculative theories regarding this epoch, but it would be great to know if this theory has some level of acceptance in the physics community. If the strong force is ...
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Precise definition of “Observable Universe” and its alternatives

The Observable Universe is generally said to contain all space that could "in principle" have had a causal impact on Earth, but the exact limits of the "in principle" causal interaction go ...
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When did the strong force separate?

Given that Grand Unification may have happened, and inflation is accepted, which of these two scenarios is better accepted; 1) The strong force broke free before inflation, and is somehow causally ...
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52 views

How to calculate the scalar amplitude when two inflations happen successively?

Consider a single scalar field with some strange potential such that slow-roll inflation happens twice when it rolls down from the high potential point to the low potential point. In-between the two ...
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44 views

Hottest period in the history of the universe

Stack exchange's tagline is 'hot questions' - so here is one that will hopefully cause some heated debate. I remember hearing that the period immediately after inflation is theorized to be the ...
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45 views

Empirical effects of cosmic inflation

Let's imagine that via some contrived mechanism the cosmos entered a new inflationary era, starting right now: Space itself started to uniformly expand faster than the speed of light. Would the ...
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185 views

Inflation problem for exponential potential

I'm trying to solve the inflation problem for exponential potential. $$v(\phi) = v_0 \exp(-\alpha \phi)$$ (it's known as barrow or power law inflation) we have two main equations: $$H^2 = 8π G / 3 ...
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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 ...
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210 views

What's the difference between eternal inflation and chaotic inflation?

Is there a real difference between eternal inflation and "chaotic inflation" theories?
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Doesn't the presence of dark energy make the flatness problem less important?

If the cosmological constant (aka dark energy / vacuum energy) were zero, then an Omega greater than 1 would mean both positive curvature and a recollapse while an Omega less than 1 would mean both ...
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Is there inflationary solution in $R^2$ theory in Jordan frame?

In the Starobinsky $R^2$ inflation model, one usually uses a conformal transformation from Jordan frame to Einstein frame in which the action can be written just like Einstein action + scalar field ...