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 the simplest model of eternal inflation with a minimal landscape viable?

It is believed that much of the string theory landscape is not physically realizable. This creates problems for the usual picture of eternal inflation, in which vacuum transitions fill the entire ...
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Is there any inflationary model or any string theory model that does not assume any symmetries as fundamental?

If I understand them right, in usual chaotic inflationary models or in string theory some symmetries are assumed as fundamental and therefore some fundamental laws of physics are assumed. But, in some ...
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What would slow-roll inflation with $\eta >1$ look like?

In studying slow-roll inflation, the two slow-roll inflation parameters $\epsilon$ and $\eta$ are usually assumed to be small. However, strictly speaking only $\epsilon$ needs to be small to have ...
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When an object crosses the future horizon, what do you see? [closed]

First, there should be a redshift due to the velocity of the object before it crosses the horizon. And then, does the object's light just shut off? Note: There are several cosmological horizon that we ...
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How do you relate the number densities of neutrinos and photons soon after the positron–electron annihilation?

I found this equation: $n_\nu = \frac{3}{4} \frac{g_\nu T_\nu^3}{g_\gamma T_\gamma^3} n_\gamma$ Where does it come from?
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How do you know that objects are accelerating from each other in space?

I know that Hubble redshift comes from the relation between the distances of objects and the Hubble parameter: $$H_0 = \frac{\dot{R}}{R}.$$ But how we differentiate between redshifts effects from the ...
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Can vacuum cause something similar to the Hawking radiation?

If my understanding is correct, Hawking radiation is caused by two virtual photons separated by the event horizon of the black hole. Then, if the universe expands fast enough, (probably faster than ...
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Multiverse theory VS Conformal Cyclic Cosmology (CCC)

Multiverse theory describes that there are many singularities taking birth and then based on their properties (like dark matter content), these may pop in and out of existence. While on the other hand,...
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Power spectrum enhancement in primodial black hole

To produce a primordial Black Hole in in the inflationary epoch, there should be enhancement in the power spectrum. Both the slow roll approximation and exact solution show this feature. My question ...
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If the universe is expanding at an accelerated rate, was it stationary at some point in time and contracting before that?

If the universe is expanding at an accelerated rate it would mean that the more we go in the past, the slower the speed of expansion must have been. Provided the acceleration was always non-zero and ...
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“Law without law” in inflation?

John Wheeler proposed that the fundamental laws of physics actually were emergent from a primordial random/chaotic underlying state. According to this view, every physical law is actually emergent. Is ...
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Are the different fields in multi-field inflation described by different Lagrangians?

The most simple models of cosmological inflation consider only one scalar field. However, there are more complex models (like hybrid inflation or multi-field inflation) which consider more than one ...
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Vacuum expectation vs ensemble average

On p.169 of Dodelson's Modern Cosmology, the following is stated: "We can compute the quantum fluctuations of the operator $\hat{x}$ in the ground state $|0\rangle$: $$ \big \langle |\hat{x}|^2 \...
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Gaussianity of single-field inflation

I have read in multiple sources (i.e. Baumann's TASI lectures on inflation, Dodelson's Modern Cosmology) that single-field inflation is supposed to produce 'nearly Gaussian perturbations'. As far as I ...
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Changes to an EM-wave that is propagating in an inflating space

I am trying to get an easier picture of what happens to an em-wave considering space expansion. My question is: If a star in a non-inflating space emits light recorded at a certain distance of the ...
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Confusion about the shrinking Hubble volume

The particle horizon is given by \begin{equation} \chi_p(\eta) = \int_{t_i}^{t}\frac{dt}{a} = \int_{a_i}^{a}\frac{da}{a\dot{a}} = \int_{\ln a_i}^{\ln a} (aH)^{-1}\ d\ln a . \end{equation} For a ...
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Is the inflation theory based on the inflaton field or electronuclear force carriers decay? [duplicate]

Some sources introduce the inflaton field as the cause of the inflation period in the big bang theory, and some others relate it to the decay of electronuclear bosons. Which one of these is ...
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Slow-roll parameter in Inflation

What is the definition of slow-roll parameter? What equation that these parameters are showed up? I read a book "Modern Cosmology" by Scott Dodelson. In chapter 6, it is just given the ...
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Physical intuition for negative pressure

Ordinarily, we think of pressure, such as the pressure of a gas as an outward push exerted on the walls of the gas container. In nonequilibrium, the pressure tries to make the volume expand. But the ...
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Is primordial power spectrum $P(k) \propto k^n$ or $P(k) \propto k^{n-1}$?

I am reading in Ryden that $P(k) \propto k^n$, where $n \approx 1$ for the primordial power spectrum. However, I read here that $P_s(k)^{n-1}$. I am confused on the differences between the different $...
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Is there a Friedmann equation form with inflation?

I have been unable to find on the Internet any form of GR similar to the 4 Omegas Friedmann equation that includes a transition from an inflation era back to a radiation era. Is it known whether or ...
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How are the alpha vacua, the Bunch Davies vacuum and Adiabatic vacuum different in context of inflationary cosmology?

I do understand that the Bunch-Davies is the most standard vacuum to consider as an initial condition, but what if there are deviations from a de Sitter spacetime that do not generically reduce the ...
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How did the Universe behave just at the end of inflation?

Edit When the inflaton field $\phi$ rolls down the potential $V(\phi)$ to the value $\phi=\phi_f$ where the slow-roll parameter $\epsilon(\phi_f)\to 1$, inflation ends. By calculating the behaviour of ...
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Has any result of Hubble parameter been obtained by observing SN UDS10Wil?

I am simply asking the question after reading Wikipedia because I am confused about the historical change of the parameter during the cosmic inflation. Knowing that as far a supernova is the more in ...
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Is it realistic for an unstable vacuum to have an infinite past, but a finite future?

Is it realistic for an unstable vacuum to have an infinite past, but a finite future? In other words, can there be a plausible scenario in which an unstable vacuum did not have a beginning, but ...
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Do cosmological event horizon evaporates like black-hole horizon?

While the inflation phase of the universe, expansion was exponential and so the universe was de Sitter-like. So, for a point-like observer, there was a cosmological event horizon. Do this horizon ...
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In Eternal Inflation Theory, what is the average distance between bubble universes?

Patches of normal space randomly condense out of the false vacuum of inflating space. What is the average distance between these patches? Another words, what is the average number of bubble patches ...
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How to calculate cosmological parameters such as scalar spectrum index and the tensor-to-scalar ratio in constant-roll method?

As we know, the scalar spectrum index and the ratio of tensor-to-scalar in the slow-roll method are obtained with a certain relation according to the parameters of the slow-roll. Now I want to ...
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Exact solution of scalar field cosmology with exponential potential [closed]

Considering a homogenious and isotropic universe described by the Robertson-Walker metric: $$ ds^2= dt^2-a^2(t)\left[\frac{dr^2}{1-kr^2}+r^2(d\theta^2+\sin^2(\theta)d \phi ^2)\right]$$ and also ...
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What is brane inflation, and can it be eternal?

What is Brane Inflation and how does it describe inflation process? Can it be eternal?
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How does the whole universe agree on the laws of physics? [duplicate]

How is it possible that the every particle in the universe agrees on the laws of physics? What enforces those laws? Might the laws change slightly across the universe in the same way the cosmic ...
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At 50% c, I go party to IC1101 galaxy, and back home. How many times can i go before the expansion of the universe will lock me on one side?

Longer version of the question: Let's say I'm an immortal being (I could be artificial) going to "party" to IC1101, one of the biggest galaxies of the universe, 1 billion light-years away ...
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Magnetic Monopoles and the Inflationary Epoch

What leads to magnetic monopoles existing before the Inflationary Epoch and becoming infinitely diluted during inflation (if indeed that is the explanation to their absence), but the electric ...
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If string theory is inconsistent with observations, why hasn't it been rejected yet?

I'm no expert on string theory, but I've been reading about it. I've been quite surprised because of how it appears to be inconsistent with observations, but hasn't been rejected yet. Examples: On the ...
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How to calculate $ |\Omega_{tot} - 1| $ at inflation time?

Suppose that we live in a universe that has the following properties: $$ |\Omega_{tot,0} - 1| = 0.001 $$ How can I calculate the value of $$|\Omega_{tot} - 1|$$ at some other time as, for example, the ...
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Angular size of the largest region in causal contact at the moment of recombination

I want to calculate the angular size of the largest region in causal contact at the moment of recombination (z = 1100) to our universe, so we have: $H_0 = 68$ (km/s)/Mpc, $\Omega_{m,0} = 0.31$, $\...
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Evolution of the curvature perturbation on super-horizon scales

energy conservation equation(1st order) in density perturbations and on superhorizon scales( $k<<aH $) implies $\delta \dot{\rho } = -3H(\delta p + \delta \rho) + 3 \dot{\Psi} ( \rho + p) $ we ...
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Solving Equation of Motion during Preheating in Mixed-$R^2$

Recently, I have an interest in Mixed Higgs-$R^2$ inflation and its preheating. However, there are some problems that I faced, one of them is solving the equation of motion in certain papers and ...
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Alternatives to the String Landscape?

Many people criticize string theory for being very speculative and far fetched (since it requires extra dimensions). Nevertheless, the string landscape is often invoked to have many variations of ...
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Derivation of Mattig's Formula

Mattig's formula for any k: How to derive this equation without using General Relativity?
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Tegmark's level 1 universe: how many universes?

In "Our Mathematical Universe" Tegmark claims that inflation theory implies the existence of an infinite set of universes. My simple question is: what kind of infinity, and why that kind ? I ...
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Why does large-field inflation cause bigger gravitational waves

I'm learning about inflation and tensor perturbations during it. I've read a few times that large-field inflation is "more important" with respect to inflation as it produced bigger tensor ...
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How superhorizon power spectrum would have looked like if there was no inflation?

As it is well known, one of the main motivations for the idea of inflation is the explanation of superhorizon CMB correlations: we observe the existence of perturbations with sizes larger than the ...
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Two different astronomical motions combined give a receding velocity greater than 'c' but with different effect on an observer

Let say a gallaxy is 15 billion light years away from us so the receding velocity caused by Hubble flow is more than speed of light which affects the relative motion of light towards Earth which in ...
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If the Universe is already infinite and is expanding, how could it be expanding to more than infinity?

There are arguers that say the Universe is streching about every its point but also tell it is infinite. How it can possibly be?Maybe we should reinterprete what infinity means.
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Could the basic fundamental laws of physics change between universes in cosmological inflationary models?

According to cosmological inflationary models, different universes governed by different effective/low-energy laws of physics could exist, but the most fundamental laws of nature would remain the same....
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Can we produce the CMB power spectrum from a given model of inflation, theoretically? If yes, how?

To the best of my knowledge, the CMB power spectrum is obtained from a statistical analysis of the observed temperature anisotropies of the CMB sky. Is there a way of getting the power spectrum ...
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What does determine the frequency of gravitational waves caused by inflation?

It is theorized that during inflation gravitational waves are produced. See this article by Guzzetti, Bartolo, Liguori, and Matarrese (Cornell University). Or this one by Liu, Guo, Cai, and Shiu (...
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Why can't we take a limiting relative frequency over nested spheres in relativistic spacetime?

The Measure Problem of eternal inflation cosmology is to determine the correct probability measure over the theoretically infinitely many individuals (or civilizations or worlds) for self-locating ...
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Binnig's fractal evolution applied to multiple universes?

Gerd Binnig, Nobel laureate in physics in 1986, proposed in his article "The fractal structure of evolution" 1 that everything in the universe, including its laws, had changed and became ...

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