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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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String Landscape and Extremal / SUSY Black Holes

I should preface this question that I am new to understanding the string landscape and swampland program and F-theory, so I apologize if my question is obvious / unclear! Recently I was reading some ...
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Geometry of Tegmark's Level I multiverse

Consider Tegmark's Level I spatially infinite multiverse: it has the usual gravity, and each local copy of some material configuration has the same gravity. But how does the geometry of the Level I ...
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Why don't galaxies have larger peculiar velocities?

I am trying to reconcile two facts: That galaxies' comoving velocities are generally close to zero, and That the universe has no preferred reference frame. Galaxies seem to move very little relative ...
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How has the size of the universe changed as a function of time? [duplicate]

Is there a plot or an equation that calculates/shows the size of the universe for each era? Preferably starting from the Big Bang, inflation and on up to today.
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How the variation of Gauss Bonnet term is done?

I am trying to do the variation of Gauss Bonnet Invariant which is $G=R^2+R_{abcd}R^{abcd}-4R_{ab}R^{ab}$ and having problem in doing the variation of $δ(R_{abcd}R^{abcd})$. Can anyone please give ...
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Does the homogeneity of space imply that the expansion of the universe is uniform?

Obviously, homogeneity implies that the density is the same everywhere at any time. However, does this imply that the expansion is uniform? By uniformity, I mean that if I pick three galaxies to form ...
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Runge-Kutta fourth order method. Integrating backwards [closed]

I am using a Runge-Kutta fourth order method to solve numerically the usual equation of motion of a background scalar field in curved spacetime with a quartic potential: $\phi^{''}=-3\left(1+\frac{H^{...
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Inflation to extract information from black holes

Suppose inflation were to occur for some brief period of time in the region of a black hole singularity such that the density decreased below the Schwarzschild radius. Wouldn't this mean we can get ...
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Did the big bang start at ONE infinitely curved point (or a 4D curved ball shrunk to a point) with an infinite density of energy?

I'm confused. In this question it is said: The simple answer is that no, the Big Bang did not happen at a point. Instead, it happened everywhere in the universe at the same time. How could it have ...
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What is the expected size of primordial black holes?

I often see it implied that primordial black holes tend to be small compared to stellar masses; Since primordial black holes did not form from stellar gravitational collapse, their masses can be ...
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A thought experiment related to the age of the universe

Okay, So, this thought experiment starts with the movie, Interstellar. In which humans went through a wormhole to a system consisting of a Black Hole. They landed on a planet (I don't remember its ...
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Quantum tunneling of dark energy from black holes

There was an article posted recently suggesting there is a very deep connection between dark energy and black holes. https://phys.org/news/2019-09-black-holes-dark-energy.html I was thinking this ...
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Vacuum decay and Coleman-de Luccia bubbles

Can someone suggest me some good and detailed books (or notes) on the problem of vacuum decay and Coleman-de Luccia bubbles?
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Energy equivalence of the Universe? [duplicate]

Let us have the following constants: speed of light $c$, gravitational constant $G$, mass of the Universe $M$ and the Hubble's radius $R$. Firstly, is it just a silly coincidence that we have the ...
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Exact solution for (simple) Reheating Boltzmann equations?

Let's say we have the Universe which is exiting Inflation, with the inflaton field $\phi$ decaying into relativistic particles (radiation $R$). Without any other assumption, the equations describing ...
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Gravitational contribution to the action for Coleman-de Luccia instanton?

In the Coleman-de Luccia calculation of the transition rate from one de Sitter minimum to another, the action for the scalar field $\phi(\xi)$ and Euclidean radius $\rho(\xi)$ is $S_E = 2\pi^2 \int \...
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If inflation is an exponential expansion, is the exponent known?

Inflation is often called exponential expansion. I can't seem to find what that exponent is. Is it 2, or 20, or completely unknown?
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'My question is about' …the size of the Universe after Inflation [duplicate]

Hitherto, I had assumed, on account of Inflation, "boom" the Universe was "out there" and it has taken light 13.6 BY to get here. However... Quoting the aerospace engineer: In my thinking if the ...
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Flat yet finite Universe

I would like to ask you this question: Let's assume that the universe is perfectly flat and big bang happened as described by our theories some 14 billion years ago. Shouldn´t, therefore, the radius ...
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World line of a photon from a distant galaxy in the $\Lambda$CDM model

The title is pretty much explaining the question: I am used to the graphs of Einstein-De Sitter model horizons: But then I don't understand 1) Are we using this kind of diagrams also now to ...
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What is the relation between comoving particle horizon $d_{hor}^c(t)$ and comoving Hubble radius $1/(aH)$ for arbitrary expansion laws?

I was learning Inflation by reading Hannu's lecture. But on page 4 of this lecture (Chapter 7 Inflation, 7.2.1 Accelerated expansion), there are some things I don't understand. The content is shown in ...
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How do we know that Dark Energy has homogeneous energy density? [duplicate]

I’ve read places that the density of Dark Energy is the same throughout the universe. If the expansion density of dark energy were the same throughout the universe, why don’t all galaxies have the ...
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Intergalactic medium and cosmic expansion

Presumably, the intergalactic medium (IGM) should get less dense as the universe expands. Also presumably, There should be a Hubble redshift to absorption lines due to the IGM. Could this provide ...
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Why is the measure problem an issue if the universe is always finite?

As a follow-up from this question, I was wondering how the measure problem applies to the idea of eternal inflation. First, why is it even a problem? As time progresses, more universes are created in ...
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How necessary is inflation given the laws of physics?

How deeply is cosmic inflation required for the laws of physics? Is inflation required for a universe remotely like ours, or is it simply a contingent on the starting conditions of the universe? For ...
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Inflation v.s. Big Bang

It is said that that transition or certain quantum rotor field, and “rolling” down into the valley (of some quantum potential), is what causes inflation to come to an end, and create the hot Big Bang. ...
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How does the cosmological constant dominate cold matter perturbations?

I have been studying inhomogeneous universe in physical cosmology, whereupon I arrive at cold matter perturbations which are dominated by various background fluids. I understood the solutions for the ...
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What exactly is the problem that Inflation solves?

There's copious documents about how Inflation solves the problem that General Relativity predicts a lumpy CMB. That influation 'smooths' out the curvature fluctuations and, so, predicts a CMB at ...
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How inflation creates a universe from nothing?

I have a basic, mostly purely conceptual understanding of Quantum Field Theory, and after lots of Youtube (thanks PBS Spacetime!) I have an idea of how inflation works to turn the vacuum into a ...
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How can an inflaton field let spacetime expand?

Whatever the Nature of an inflaton-field, how did it make spacetime grow at an incredible rate? A little speck of spacetime was inflated to the entire observable Universe and everything beyond in very ...
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Why is momentum divergence from energy release not considered in Big Bang models?

From the formation of subatomic particles to the formation of atoms to the nuclear fusion in stars to the explosions of supernovae, the process of conversion of rest-mass energy from fields into ...
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Higgs Field before or after Cosmological Inflation?

Question: When exactly did the Higgs Field begin to exist (before cosmological inflation or after cosmological inflation)?
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Does an expanding universe assume a space within which the expansion is happening? [duplicate]

When I read about the expanding universe and inflation I often see pictures like this: (Source: https://en.wikipedia.org/wiki/Inflation_(cosmology)) or explanation like this: For getting an idea ...
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Multiverse and the anthropic principle? [closed]

In this paper (https://arxiv.org/abs/hep-th/0211048) by physicist Andrei Linde, the multiverse concept, the anthropic principle, quantum cosmology and inflationary cosmology are analyzed. In the ...
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Why physical / cosmological models that have been falsified weren't abandoned? [closed]

Before anything, I'd like to say that I'm a layman (non physicist) and english is not my main language; I apologize if my choice of words make me sound rude / arrogant, that is not my intent. I often ...
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Are there other theories (apart from string theory) that combined with inflation, would produce universes with different laws?

In chaotic inflation, space would stop expanding in some points, creating hubble volumes that could experience different spontaneous symmetry breaking, which would result in different properties, such ...
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Cosmological Inflation: If Photon expands, why not other matter?

I keep repeatedly reading in many Stack Exchange and Quora questions that space of universe expands but particles (matter) don't, see e.g. this Phys.SE post. The reason given is that particles are ...
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Could gravitational waves be the cause of inflation? [closed]

Ok, crazy idea time. Context: https://www.livescience.com/65441-gravitational-wave-memory.html Quick lay summary: Apparently gravitational waves alter the structure of the space they pass through. ...
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Tests of inflation theory

So I'm following a course in Early Universe Cosmology right now. For the next lecture we have to solve a few questions about inflation, just as preparation. I read some closely related lecture notes ...
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Is it possible that black holes generate space? [closed]

Suppose that there is a limit to the strength of a gravitational field. Then, if the mass is added to a black hole, the gravity term in the EFE will not increase, so the spatial expansion term must ...
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Regarding the initial curvature conditions in simple single scalar field slow roll inflation models

So while learning about modelling inflation using a single scalar field slow roll, most authors seem to use the Friedmann equation with the spatial curvature taken to be 0. Now one of the precursors ...
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What actually is the flatness problem?

One of the Friedman equations is given by $$ H^2\equiv\Big(\frac{\dot{a}}{a}\Big)^2=\frac{8\pi G}{3}\rho-\frac{k}{a^2},\tag{1} $$ which fixes the evolution of $a$ (with given $\rho(t)$) if values for $...
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Axion CDM analogous to reheating?

In a paper on Axions Peccei writes: When the Universe goes through the PQ phase transition at $T ∼ f_a > > Λ_{QCD}$ the QCD anomaly is ineffective. As a result, early in the Universe $< ...
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Vanishing integral in deriving stress-energy tensor from action

In the derivation of the energy-stress tensor for a scalar field (context: Inflation Theory for Cosmology) by varying the action with respect to the metric, the integral over spacetime that is ...
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When space expands where do the energy of the gravitational wave dissipate to? [duplicate]

I think it is safe to say that gravitational wave do not dissipate unless it met matter along the way imparting some of it's energy to cause some distortion or when it's frequency is stretched even ...
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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. ...