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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Black Hole Ripped Apart

Could a black hole be ripped apart if it passed directly between two other black holes that were millions of times bigger?
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Bunch-Davies initial condition

I have the Mukhanov-Sasaki equation in terms of $Q(t)$ \begin{align*} Q''(t)+3HQ'(t)+k^2Q/a^2+\left(3\phi'(t)^2-\phi'(t)^4/2H^2+2\phi'(t)V_\phi/H+V_{\phi\phi}\right)Q=0,\ u=aQ \end{align*} and also ...
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What means Alan Guth's Free Lunch Principle for the universe?

Alan Guth calls the universe the ultimate free lunch. What does he mean by this? Does he mean that the total energy of the universe is zero? So the total energy of all particles is the negative of the ...
Il Guercio's user avatar
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How big was the universe after inflation? [duplicate]

If we assume the universe is a closed 3-sphere, how big was the universe after inflation, compared to nowadays? Was, relatively, most space already there? If we envision the universe as a 2-sphere, a ...
Il Guercio's user avatar
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Intuitive explanation of COSMIC TIME?

I came across the following statement, while studying a Newtonian model for cosmic expansion: "If $R(t)$ is the scaling factor, we can define the Hubble parameter as $H(t)=\frac{\dot{R(t)}}{R(t)}...
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Could cosmic inflation restart?

Is it possible for a region of space in our universe to reenter an inflationary state? For example, if a particle accelerator collision of sufficiently high energy recreated conditions under which the ...
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Why is there an infinite supply of energy in slow-roll inflation?

The physical model of inflation includes a metastable false vacuum, or a slow-roll field on a flat potential. In either case, I just realized how this is completely insane. With the exponential growth ...
Bababeluma's user avatar
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Tachyonic instabilities [closed]

How to find tachyonic instabilities for some parameter ranges in the $f(R)$ gravity model? I have tried to find the parameter ranges for exponential $f(R)$ model, Starobinsky $f(R)$ model and ...
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Time evolution of scale factor for FRW solutions

I'm reading TASI Lectures on Inflation(https://arxiv.org/pdf/0907.5424.pdf). On page 20, it says ... also called the Friedmann Equations $$\tag{21} \boxed{H^2=\left(\frac{\dot{a}}{a}\right)^2=\frac13\...
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False Vacuum State (QFT)

I am wondering if someone can refer me to a proof that the false vacuum state is a natural consequence of scalar field theories? I see that being said in a lot of texts on cosmology when discussing ...
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Numerical solution for the Mukhanov-Sasaki equation with Bunch-Davies vacuum state

I have the Mukhanov-Sasaki equation in terms of $u_k$ \begin{align*} u''_k(\tau)+\left(k^2-\frac{a''(\tau)}{a(\tau)}+f(\tau)\right)u_k(\tau)=0 \end{align*} and also the initial condition from Bunch-...
Julian Yussef's user avatar
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How to select proper values to solve Bunch-Davies initial condition?

I am trying to solve the Mukhanov-Sasaki equation for a Starobinsky potential $V(\phi(t))=3/4m^2M_P^2(1-e^{-\sqrt{2/3}\phi(t)})^2$. I could change the equations so that $m^2$ does not appear and chose ...
Julian Yussef's user avatar
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"Boltzmann" equation for radiation (Reheating period)

These equations are given in many papers as the "Boltzmann equations" (without derivation) governing the reheating period, where $\rho_\phi$ is the energy density of the decaying inflaton ...
Rajat Mondal's user avatar
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Difference between new inflation and chaotic inflation

I'm trying to understand the difference between new inflation and Linde's chaotic inflation. From what I understand, according to the old inflation, during inflation empty space remains empty, so its ...
Math boi's user avatar
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What is the intuition behind the decrease in comoving Hubble radius during inflation and then its increase later on?

We know that the comoving Hubble radius decreases during inflation when the universe is exponentially expanding and then increases during matter and radius domination. What is the reason behind this? ...
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Does inflation theory assume a finite universe?

Inflation theory has it that the early universe was causally connected, and could “mix”, hence explaining relative homogeneity of the CMB. The universe then rapidly expanded and became causally ...
Captain Chicky's user avatar
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What would the cosmic microwave background radiation look like in a hyperspherical universe?

I was thinking about what things would look like in a hyperspherical universe. How would galaxies look as they got closer to the other side of that hypersphere? It seems like if a galaxy were on the ...
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Does General Relativity, without Cosmic Inflation, predict a perfect blackbody for the CMB radiation?

My understanding is that the universe did not have enough time to thermalize before the epoch of recombination, so many patches of the sky were not in causal contact with each other, which means they ...
The Shepard's user avatar
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Can either of LISA, NanoGrav or LIGO measure the polarization of gravitational wave background (GWB)?

Polarization in GWB should carry as much important information as in CMB. However, I've done some superfluous literature research and found little discussion. Is there any planned project for ...
Bababeluma's user avatar
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Do matrix models capture the string landscape?

Essentially what the title asks-- are matrix models, such as BFSS, believed to capture in any way the large possible space of false string vacua, for instance as saddles in the action with nonminimal ...
Panopticon's user avatar
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What causes a big rip?

If dark energy has $w<-1$ you get the Big rip scenario, where dark energy becomes more and more powerful until it eventually rips all matter apart. Why does this occur? Why does having $w<-1$ ...
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Does the expansion of the universe affect small objects? [duplicate]

If the expansion of the universe happens uniformly, how does this affect small objects? For example, are the distances between protons and neutrons inside a nucleus actually expanding? Is the nucleus ...
Meatball Princess's user avatar
4 votes
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What if the cosmological principle does not hold at larger scales?

Quite naturally, the observable Universe is the only bit of the Universe we can extract information from, as light from farther away has not reached us yet, and there are zones from which we'll never ...
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Green's function of an equation of motion of $\zeta$ field

I'm writing a thesis on inflationary cosmology. I've come across a background equation of motion of my $\zeta$ field of the form $$ \partial_\tau(z^2(\tau)\partial_\tau\zeta_{\textbf k}(\tau)) + k^2z^...
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Need explanations about notions of sub-hubble and super-hubble scales

I have often seen in the literature the notions of sub-hubble, super-hubble scales as illustrated in this diagram: I don't understand this diagram: on the abscissa is the scale factor well ...
guizmo133's user avatar
3 votes
3 answers
596 views

What's so "quantum" about quantum fluctuations in the CMB?

I've heard that fluctuations in the CMB provide support for inflationary theory, as they are thought to be amplified quantum fluctuations of the inflaton field. My question is, what is so "...
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Inflation in new aeons (cyclic cosmology)

I have a question pertaining to Penrose's ideas about cyclic cosmology. As predicted therein, the end of each cycle comes about when massive particles are extinct and time is no longer measured. What ...
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Duration of inflationary epoch

Why is it thought that the inflationary epoch of the universe lasted approximately $10^{-30}$ seconds and why did it take the inflaton (assuming its existence) to release the energy contained itself ...
Antoniou's user avatar
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Analytic expression for a universe without a big bang [duplicate]

I was reading introduction to modern cosmology by Andrew Liddle. On page 56 he shows a graph of the $\Omega_{\Lambda}$, $\Omega_{0}$ plane and there's a region where no big bang is needed, later on ...
Muñoz Castro Yusef's user avatar
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How was the universe once small enough to be subject to quantum mechanical effects?

I have often read that our universe was once small enough to be subjected to quantum mechanical effects, potentially altering how our universe turned out. This is a large theme in Laura Mersini-...
cosmicpawn's user avatar
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Calculating parameter expression in the evolution of small-scale sub-horizon modes

I'm studying from the Dodelson book on Cosmology and I got stuck on a specific derivation. In this derivation I need to compute $$\frac{d}{dy}\left(\frac{1}{ayH}\right).$$ Here $y= \frac{a}{a_\text{eq}...
Geigercounter's user avatar
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Visualizing the Hubble Sphere

I have viewed the definitions of the Hubble Sphere and related cosmological concepts, as well as various explanations, yet Im still struggling to comprehend a full visualisation of this, which I would ...
Michael D's user avatar
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Question on cosmological parameters and slow-roll potential

Given a slow-roll potential $V (\phi)$, how do the cosmological parameters (see e.g. the Dodelson book on Cosmology, section 8.7) relate to this potential? I'm a bit confused how parameters such as ...
Geigercounter's user avatar
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No symmetries in the universe at the Big Bang...?

I apologize in advance if this is a stupid question but... According to some scenarios about the beginning of the universe (namely cosmological inflation), in layman terms, everything was born out of ...
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Initial Conditions for Inflationary Equations of Motion

I am attempting to solve the equation of motion for single field inflation. The equation of motion is given by \begin{equation} \ddot{\phi} + 3H\dot{\phi} + \frac{dV}{d\phi} = 0 \end{equation} In ...
MarcosMFlores's user avatar
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What does $w=1$ mean in cosmology/inflation?

I got a problem where I had to calculate the equation of state of a scalar factor $a\propto t^q$. I found that, solving the Friedmann equation, $\rho_\Phi=\frac{3M_p^2q^2}{t^2}$, which is equal to $\...
Julian Yussef's user avatar
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In the Steinhardt's bouncing cosmology, how would the CMB differ for patches close to pre-existing black holes

In Steinhardt's bouncing cosmology model, during the contraction phase the Hubble radius shrinks to microscopic sizes, although the overall contraction of the universe is much less significant. Each ...
cosm_ques's user avatar
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What conclusions can be drawn from the CMB TE polarization spectrum?

Does the polarization spectrum TE measured by the Planck and WMAP satellites show evidence for superhorizon fluctuations at low multipoles and are these evidence for pre-bigbang inflation?
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Superhorizon fluctuations from CMB polarization spectrum TE

The CMB cross-corelation polarization spectrum TE measured by the Planck and WMAP satellites shows a non-zero negative signal between multipoles l = 30 ... 200. a) Is this evidence for superhorizon ...
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Gauge-Invariant Variables in Cosmological Perturbation Theory

So I'm referring to these lecture notes for the gauge-invariant variables $\zeta$ and $\mathcal{R}$ (around p. 48), the curvature perturbation on uniform-density hypersurfaces and comoving curvature ...
M. V.'s user avatar
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How does the quantum landscape of Mersini-Houghton's multiverse theory become physical?

In her new book (Before the Big Bang), Dr. Laura Mersini-Houghton elegantly describes the "quantum landscape of the multiverse", an abstract quantum field of energies where an inflaton (...
DouglasPhillips's user avatar
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Books for studying field theory in cosmology

I have a background in general relativity (Carroll and Wald) and Quantum field theory (Peskin and Mark Srednicki). Which books would you recommend for learning the following topics: Cosmological ...
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Primordial gravitational waves evolution equation

I'm reading the review by Domenech "Scalar induced gravitational waves review" and he says that equation 3.15 $$\ddot{h}_{ij}+3H\dot{h}_{ij}-a^{-2}\Delta h_{ij}=S$$ where I use $S$ as an ...
Stefano98's user avatar
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How is the universe becoming increasingly unreachable for things traveling at speed of light?

I've seen a few articles like this that say the majority of the universe is practically unreachable to us, even if we were to travel at the speed of light. My understanding is that there is enough ...
Sidd Singal's user avatar
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Inflation, dark energy and symmetry breaking

Aside as the inflaton has been hypothesized to have arisen from the breaking of the $SU(5)$ GUT symmetry, could dark energy have arisen as a weaker inflaton from electroweak symmetry breaking?
Raul's user avatar
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Can we infer the size of the whole universe from its expansion rate? [closed]

If the universe inflated to 100 billion km in its first second, that suggests only 1/160,000 of it was observable from any point at that moment. The expansion rate slowed after that, of course, but ...
Doradus's user avatar
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2 answers
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The slowing of expansion in the matter dominated era

On all the graphs of the inflation of the universe, the era dominated by matter is slowing the rate of expansion. With an intuitive explanation (for all you science communicators out there) could you ...
Jason Verreault's user avatar
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An intuitive explanation of the relationship between general relativity and the scale factor

With as little math as possible your understanding of the how the scale factor and general relativity relate. Is the premise that the cosmic scale factor is a consequence of the calculations of GR or ...
Jason Verreault's user avatar
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The precise definition of a number of e-folds in inflationary theory

Cosmological parameters and their correspondence with recent data are very important, so I have two basic questions, what is the exact meaning and definition of the number of e-folds, and for what ...
Saber's user avatar
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4 votes
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Why does non-baryonic matter give structure formation a head start?

This image is from the textbook by Ryden. It shows that the density perturbation was able to grow earlier if there were non-baryonic dark matter, why is that?
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