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Questions tagged [cosmological-inflation]

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 and questions tagged by inflation should pertain to this era and not be about the expansion of the universe in general.

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Is inflation a possible explanation for what started the expansion?

Alan Guth stated in this article But let me start the story further back. Inflationary theory itself is a twist on the conventional Big Bang theory. The shortcoming that inflation is intended to ...
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Why was it cold during inflation?

During inflation, spacetime is approximately de Sitter and there is a cosmological horizon; in analogy with Hawking radiation, there should be a de Sitter temperature $T \sim H$. This temperature has ...
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Physical explanation of Dirac-Born-Infeld (DBI) inflation

I am studying the Dirac-Born-Infeld (DBI) inflation model and came across this question in a past exam paper from Cambridge that considered the following Lagrangian: $$\mathcal{L}=\sqrt{-g}A(X,\phi)$$...
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How is Inflation able to create an infinite amount of energy?

Follow up to this question here: If the universe is flat, does that imply that the Big Bang produced an infinite amount of energy? As I understand Inflation theory, some time after the Big Bang, the ...
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Robertson-Walker metric and cosmic homogeneity

The Robertson-Walker metric is of the form $$\tag{1} ds^2 = dt^2 - a(t)^2 \Big(\frac{dr^2}{1 - kr^2} + r^2 d\theta^2 + r^2 \sin^2\theta \, d\phi^2 \Big).$$ My question is related to the $a^2(t)$ ...
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Would a charge imbalance act like dark energy?

I realize that there are theoretical reasons to reject the idea that the charges on electrons and protons may not be exactly equal and opposite; and I am not suggesting that they're not. Edited 12/20/...
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How to justify studies on fractal cosmology?

What are the arguments (theoretical and experimental) to support or to justify a fractal distribution of matter on all scales in cosmology? I see only one justification: On some small scales, matter ...
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Could the horizon problem be explained by a finite universe instead of inflation?

Suppose the universe is finite (either closed or open with a non-trivial topology), any point could be within the horizon of another.
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How can the Friedman Equation produce negative pressure or density?

As I understand it, the Friendman Equation provides the driving mechanism for Inflation.$$\frac{\ddot a}{a}=-\frac{4\pi G}{3}\left(\rho+\frac{3p}{c^2}\right)$$If $\rho$ or p is negative enough, you ...
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Particles, fluctuations and the quantum vacuum: is this right?

After answering a question on quantum fluctuations Could quantum fluctuations spawn real matter?, I got into conversation with E. D. Kramer (to whom thanks) and in the end it may be that we had a ...
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Could quantum fluctuations spawn real matter?

Would it be plausible for fluctuations in the QED vacuum to spawn actual matter (such as quarks, electrons the constituents of a hydrgen atom) given enough time and space?
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Numerical solution to Mukhanov-Sasaki equation

I am trying to figure out how to solve the Mukhanov-Sasaki equation to compute the power spectrum of an inflation potential that exhibits an ultra slow-roll phase that gives rise to an enhancement in ...
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How was electrical charge formed in the Big Bang?

We know that fundamental particles (Quarks, electrons, etc.) were formed a while after the Big Bang. How was their electrical charge (its value and sign) determined? Was electrical charge present in ...
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Meaning of the simplest potential of quintessence models. Fields in denominator?

I am reading Sec. 1.12 of the Cosmology book by Weinberg. In this section he explains the very simple model of quintessence which attempts to provide a dynamical explanation of the smallness of the ...
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CMB homogeneity: Inflation vs. common initial conditions?

As I understand it, inflation was proposed to provide a mechanism by which now-causally disconnected regions of the universe could have once been in causal contact, and thus explain correlations in ...
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How are the tensor-scalar ratio and tensor spectral tilt in the CMB measured for massless and massive power spectrums?

When testing the tensor-scalar ratio and the tensor spectral tilt using CMB data, does it matter whether the power spectrum is massive or not? i.e. is the tensor-scalar ratio $r_{total}$ just $$r_{...
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How did inflation affect time-like space-time?

Alan Guth gave an overview of inflation in a series of videos for World Science U. The emphasis is on how inflation expanded a patch of space to the size of a marble, with no mention of how time-like ...
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How might cosmic inflation affect chemistry and nuclear interactions?

How might cosmic inflation affect chemistry and nuclear interactions? Hypothetically, if I am alone (wearing a spacesuit) in a large but empty universe, and the inflation of this universe is such ...
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Temperature due to the cosmological horizon during inflation

During inflation, the de Sitter space has a cosmological event horizon. This horizon exists because farther than the horizon distance the expansion carries light away from the observer faster than the ...
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After inflation ended, did the expansion slow down to non-inflationary expansion because of gravity?

Assuming that inflation occurred, it accelerated from the previous expansion to inflationary expansion. After inflation ended, did the inflationary expansion instantly change into the previous ...
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Quantum fluctuations producing CMB fluctuations also cause inflation to be eternal?

It is believed that quantum fluctuations in the inflaton field caused inflation to end at different times in different places, which led to CMB fluctuations (1 part in 100,000). Eternal inflation ...
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The potential of Starobinsky model of inflation

I try to study this paper about Starobinsky model of inflation https://arxiv.org/abs/1809.09975 It refers in Equation (14) for the model potential, but I can’t understand where did it come from ? ...
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Weyl transformation of the metric

In this reference https://arxiv.org/abs/1809.09975 Ketov, et al. “Extending Starobinsky Inflationary Model in Gravity and Supergravity.” [1809.09975] Extending Starobinsky Inflationary Model in ...
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What causes fluctuations in the inflaton field value?

From this article During inflation there are quantum fluctuations in the inflaton field. And this The field φ experiences quantum fluctuations, as the uncertainty principle tells us it must. ...
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what are possible explanations for the larger scale anomaly in Planck satellite's data?

In the Planck satellite's image of the Cosmic Microwave Background (CMB), there have been anomalies, the most important of which is a deficit in the signal at large angular scales on the sky, which is ...
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Does $\Lambda$CDM include inflation?

$\Lambda$CDM obviously includes dark energy (the $\Lambda$) as well as cold dark matter (CDM). Does it also include cosmic inflation? I've not seen a clear answer to this. Wikipedia's article on ...
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Why Alan Guth limit inflaton field mechanism into range $10^{-35}$ to $10^{-34}$ seconds to justify an isotropy and homogeneity?

The field, originally theorized by Alan Guth, provides a mechanism by which a period of rapid expansion from $10^{-35}$ to $10^{-34}$ seconds after the initial expansion can be generated, forming a ...
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Does Coleman-de Luccia instanton approach a Hawking-Moss instanton?

Suppose a Coleman-de Luccia instanton terminates in the basin with the true vacuum between the top of the potential barrier and the field value with potential energy equal to the potential energy of ...
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What are some verified “out of sample” predictions of cosmic inflation?

I'm curious about the "out of sample" (forgive me, my background is in data / statistics / machine learning) predictions of the theory of cosmic inflation. By that I mean phenomena that had not been ...
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Why does inflation end when the potential becomes too steep?

Inflation ends when the potential becomes too steep. Is it because kinetic energy increase when the potential becomes steeper?
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Does reheating occur when inflation ends or when the field reaches minimum?

Link for the picture The inflaton field can be represented as a ball rolling down a hill. During inflation, the energy density is approximately constant, driving the tremendous expansion of the ...
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How valid are Paul Steinhardt's criticism of inflationary theory? [closed]

I recently read about Paul Steinhardt's criticism of inflationary theory, which can be boiled down to "if inflation predicts everything (c.f. the multiverse), then it also predicts nothing, and if it ...
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Does the shape of the potential in chaotic inflation have to have this particular form?

(a) represents New inflation ; (b) represents Chaotic inflation. From what I understand, chaotic inflation means chaotic initial conditions, i.e. different initial inflaton field values in different ...
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If Time and Space are intrinsically linked and space is ever expanding then surely time is slowing down [duplicate]

When we try to imagine the initial expansion after the big bang we see with the CMB that the universe went from initially smaller than a hydrogen atom to what we see today. However, when we try to ...
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Primordial gravitational waves power spectrum and parity invariance

I'm trying to learn about primordial gravitational waves. These are metric tensor perturbations and the power spectrum of these perturbations in Fourier space is given as $$\langle E_{ij}(\textbf k)...
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Is the inflaton field baryon symmetric?

The theory states that after inflation ends, the energy stored in the inflaton field decays to produce particles. Does the inflaton field have baryon number associated with it? Is the field baryon ...
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How do we know normal expansion without inflation is not enough to dilute the density of magnetic monopoles?

Assuming magnetic monopoles was produced in the early universe. However we don’t see any of them. Wouldn’t expansion even without inflation dilute their density enough that they are unobservable?
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Can a scalar field also has positive or zero pressure?

In inflation theory, the inflaton field produce negative pressure to drive inflation. But now I’m going to ask about scalar fields in general, not the inflaton field. Can a scalar field also has ...
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How does the scale factor and further the Hubble constant depend on the inflation potential?

I've found standard derivations showing how one can integrate the Friedmann equation to obtain $a(t)$ given $P_{tot}$ and $\rho_{tot}$. I'd like to know how $a(t)$ depends on the inflation potential.
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Relationship between power spectra, density perturbations and temperature?

I am trying to understand how density perturbations relate to temperature fluctuations in the CMB. I understand the physical effects involved, but my question is how is the density power spectrum ...
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Was the universe already expanding before inflation occured?

Was the universe already expanding before inflation occured or did inflation cause the universe to start off expanding? By “cause it to start off expanding” , I mean the cause of the initial ...
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Why is slow-roll is prefered over non-slow-roll inflation?

Wikipedia says that in new inflation, the slow-roll conditions must be satisfied for inflation to occur. What is fast-roll or non-slow-roll inflation and why is slow-roll is prefered?
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Why should LTB dust be comoving?

In many research papers about inhomogeneous cosmology, one often considers spherically symmetric (LTB) spacetimes where in the co-ordinate frame $(t,r,\theta,\varphi)$ wherein the metric assumes the ...
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What is $\tau$ and $\sigma$ in a geodesic $ψ(x) = (\tau(x),\sigma(x))$?

I'm trying to replicate the results of this paper (Eternity in 6 hours, written by Stuart Armstrong and Anders Sandberg). On pages 14-15, it discusses the path of an intergalactic probe that is ...
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Would eternal inflation be really eternal since quantum fluctuations are usually very rare and very small?

I’ve read somewhere that quantum fluctuations in the inflaton field are usually very rare and very small. If the effect of quantum fluctuations pushing the potential uphill is too rare and too small ...
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Heat death in eternal inflation

Heat death is the predicted fate of the universe. Eternal inflation theory states that new hydrogen atoms are created in each pocket universe so that means new hydrogen atoms are still being created ...
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Inflation of the Universe as Bose Einstein Condensate (Literature)

I'm searching for literature in the field of cosmological models which use a Bose-Einstein-Condensate (BEC) to model the process of inflation. Especially the analytical results the cubic BEC models ...
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Entropy estimation in Guth (1981)

I am trying to understand step-by-step Guth's famous paper "Inflationary universe: A possible solution to the horizon and flatness problems" I am stuck at his discussion of the flatness problem. On ...
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Alexander Vilenkin - The Universe probably had a beginning [duplicate]

Is it true that the Universe can not have an eternal past? It seems like Alexander Vilenkin tries to argue this? Does this imply that the Universe had a beginning? Link to his publication regarding ...
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Is stellar luminosity vs redshift calculated incorrectly?

In this paper the author, T.X. Zhang, asserts that the luminosity of distant supernovae normally is calculated incorrectly. His point (if I understand his paper) is that "luminosity" should mean ...