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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 there a cosmological model where the observable universe is bidirectionally infinite and yet finitely bi-limited?

Is there a cosmological model where the observable universe continues to shrink as we go back in time, and continues to expand as we go forwards in time, and such that at both directions it never ...
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Tegmark's level 1 multiverse - why does infinite set of universes imply existence of a universe almost identical to ours?

In "Our Mathematical Universe" Tegmark claims that inflation theory implies existence of (countably, it seems to me) infinite set of universes. He says that from this follows existence of a universe ...
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Spectral Index and inflationary models

The question that I am trying to answer is- what is the effect of changing primordial spectral index ns, on the power spectrum, which will be set according to several inflationary models. And is ns ...
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In what ways is eternal inflation less certain than standard inflation? [closed]

Eternal inflation is the idea that inflation could be eternal due to the effect of quantum fluctuations of the inflaton field. Why do some cosmologists accept inflation, but consider eternal ...
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Why does a universe with total positive energy eventually collapse in a crunch?

While reading about negative energy in the following Wikipedia page, I came across a statement that, if in a universe positive energy dominates, it will eventually collapse upon itself in a crunch. ...
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How the cosmic inflation solves the horizon problem (an exact solution)?

I am reading an article, Inflation and CMBR by Charles H. Lineweaver. https://www.mso.anu.edu.au/~charley/papers/canberra.pdf (Page 5/13) He explains the inflation period as the shrinking of the ...
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$z$ (redshift) at the inflation start up time?

The $q$ parameter is at present -ve which implies accelerated expansion , hence we can approximate our universe now to be dominated by dark energy since dark energy provides exponential growth $~e^{\...
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How are parameters in inflation potential determined

This is a question on how to determine the parameters in a given inflation potential. I have been studying a particular inflation model (https://arxiv.org/abs/1805.09483) which works with a potential ...
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Hubble - Cosmological vs Doppler Red Shift

When we learnt about the Hubble Constant at school we were taught that Hubble had observed Red Shift due to the Doppler Effect, and thus the universe (and space time itself?) must be expanding. ...
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Horizon Problem: How did different regions of space acquire different temperatures?

I'm trying to understand the Horizon Problem. Inflation describes how non-causally connected parts of the universe (that we see today) could once have been in causal contact. The reasoning goes that ...
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How would primordial black hole forms if expansion of space overwhelms gravity? [duplicate]

I read that density is quite high in the early universe and many speculate that primordial black hole can form and would probably have a mass similar to a human ovum(egg cell). Usually black hole only ...
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Is cosmic inflation slow rather than fast

According to cosmic inflation models, there is an early period where $\Lambda$ dominates and the scale factor grows exponentially. Among other things, this helps to give a reason for large-scale ...
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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 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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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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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 ...