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 ...

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Empirical effects of cosmic inflation

Let's imagine that via some contrived mechanism the cosmos entered a new inflationary era, starting right now: Space itself started to uniformly expand faster than the speed of light. Would the ...
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Inflation problem for exponential potential

I'm trying to solve the inflation problem for exponential potential. $$v(\phi) = v_0 \exp(-\alpha \phi)$$ (it's known as barrow or power law inflation) we have two main equations: $$H^2 = 8π G / 3 (1/...
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Inflation and scalar spectral index

I've been reading that the results from the Planck satellite constrain a number called the "scalar spectral index" to be 0.96 rather than 1 at the 5-sigma level. This is supposed to be big news, but ...
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What's the difference between eternal inflation and chaotic inflation?

Is there a real difference between eternal inflation and "chaotic inflation" theories?
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Doesn't the presence of dark energy make the flatness problem less important?

If the cosmological constant (aka dark energy / vacuum energy) were zero, then an Omega greater than 1 would mean both positive curvature and a recollapse while an Omega less than 1 would mean both ...
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Is there inflationary solution in $R^2$ theory in Jordan frame?

In the Starobinsky $R^2$ inflation model, one usually uses a conformal transformation from Jordan frame to Einstein frame in which the action can be written just like Einstein action + scalar field ...
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Why does the curvature of space decrease during inflation but increase after it?

According to the Friedmann equation, curvature of space will increase with time/expansion of space, but I've also read that during Inflation, the expansion caused the Universe to flatten out. What is ...
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109 views

How did inflation lead to the expansion of space?

Big bang Theory gives a scientific explanation of the evolution of the Universe, where the scientific picture of it starts with Universe(space) uniformly filled with matter and energy, already ...
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Cosmological inflation in LQG/LQC

I seek the state-of-the-art report on how cosmological inflation is described by loop quantum cosmology. I know that LQG/LQC predicts a big bounce to replace the classical big bang singularity of GR. ...
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Would quantum fluctuations cause problems for scalar-field inflation?

Wheeler once said that spacetime would be highly curved at very small scales because of the uncertainty principle for energy-momentum. In which case the spacetime becomes very bumpy and not smooth ...
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What is the form of Higgs potential, when written using higgs mass and quartic coupling.

Usually we write Higgs potential as $V=-\frac{1}{2}m^2 \phi^2 + \frac{1}{4}\lambda \phi^4$ What are the present reliable values of parameters '$\lambda$' and '$m$'? Is '$m$' used here Higgs mass? If ...
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Drawbacks of single-field inflationary models with $\phi^2$ or $\phi^4$ potential?

I am aware that existing models of inflation, especially the single field chaotic inflation with quadratic or quartic potential, e.g. $$ V = \frac12 m^2 \phi^2 \qquad \text{or} \qquad \lambda \phi^4 $$...
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Is the CMB Cold spot growing or shrinking?

What do we know about the nature of this region of the sky? is that region entirely devoid of galaxies? Could it be a bubble void, and we are simply unable to see the galaxies that are on the ...
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Gravity's force on space

Here is a quote from Brian Greene, The Fabric of the Cosmos: Space, Time, and the Texture of Reality, p. 273: “The early universe provided an arena in which gravity exerted its repulsive side with ...
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Inflation in a closed universe or a stage 1 multiverse?

With the discovery of gravitational waves, Max Tegmark has been using this to promote his level 1 multiverse in that the universe is open (non-compact) and everything duplicates. My question is, are ...
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Why do “Quantum Fluctuations” need Inflation to grow into cosmic scales?

This is a follow up to How do quantum fluctuations lead to overdense regions in the CMB? (which still hasn't been answered). The general logic of Inflation (if anything about the theory can be ...
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How do quantum fluctuations lead to overdense regions in the CMB?

I've read a lot of work about Inflation but yet to find a cogent description where someone explains exactly what 'quantum fluctuations' are and how they led to overdense regions in the CMB. I get the ...
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Why did the inflation era not produce decompactification of the extra dimensions of string theory?

My question is undoubtedly naive, due to lack of background, but any answers, or simply comments with short explanations of my incorrect assumptions, would be appreciated. I must point out this ...
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photons in expanding space: how is energy conserved? [duplicate]

If a photon (wave package) redshifts (streches) traveling in our expanding universe, is it's energy reduced? If so, where does it go?
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What was the diameter of the (observable?) universe at the end of inflation?

One reference says that during inflation, the universe expanded by a factor of 10**26. But I could find no reference to what the diameter was at the beginning. (Perhaps not surprisingly.) Is there an ...
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Stopping inflation, dark energy and switching it on again [duplicate]

Inflation is the current paradigm to explain several big problems of current cosmological models. My question is simple. Why or what stopped inflation and why is the cosmic acceleration behaviour ...
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Did the initiation of the Higgs Field and the inflationary period occur simultaneously?

My question is: Both of these concepts involve a phase transition and they both started, as far as I know, early in time, so are the above two ideas linked in any way? My first source for this query ...
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Connection between the energy scale when inflation starts, ends, the inflaton mass and the reheating temperature?

Let's assume inflation starts at some energy scale $E_s$ and ends at $E_e$. Is there anything general (I know there are many inflation models) one can say about the inflaton mass and the reheating ...
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In a perturbative FRW cosmology, why do constant-density hypersurfaces define a good gauge?

It appears to be common in the discussion of perturbative FRW cosmologies to choose a gauge using hypersurfaces for special values of some quantity, like surfaces of constant density $\rho$, constant ...
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Speed of inflation [duplicate]

The speed at which matter separated and formed our universe as we know it today was faster than the speed of light (I think its called Planck time)? Anyway how does this differ from saying that '...
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Is it plausible for spacetime to be shaped something like a torus? [duplicate]

I have heard three theories for how space-time is shaped, flat, sphere-like, or saddle-like. Flat is the most likely, as all our measurements implies that space time has curvature close to 0. Is it ...
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Can you compare curvatures in space, spacetime and hidden space?

Spacetime curvature is given by the cosmological constant, that produces a De-Sitter spacetime. It is non-zero. But space curvature is nearly zero (how close to zero, compared to the cosmological ...
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Is Dark Matter accounted for in early universe inflationary models?

In the early universe there must have been an abundance of dark matter unless it formed by some unknown process later on. If it were present, is this significant and factored into our models?
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What is the minisuperspace Lagrangian for gravity plus a scalar field?

In this paper by Sean Carroll and Grant Remmen, in equation (11) they write a Lagrangian of the form $$\boxed{\mathcal{L}=3a\left(k-\dot{a}^2\right)+a^3\left[\frac{1}{2}\dot\phi^2-V(\phi)\right]}$$ ...
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How to explain the homogeneity of the universe through a physic model [duplicate]

If in general, two objects homogenize themself by combining it's parts, why the horizon effect, based on a big bang model, excludes such an important physical interaction process? I wonder if this ...
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Correlation length during phase transitions in early Universe

During phase transitions of the second kind topological defects may form on the bounds of two areas separated by correlation length. In early Universe during phase transitions correlation length $l_{...
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301 views

Can anyone explain the unit for rate of expansion of universe?

If you google for 'what is rate of expansion of universe' you get Space itself is pulling apart at the seams, expanding at a rate of 74.3 plus or minus 2.1 kilometers (46.2 plus or minus 1.3 miles)...
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Additional merits to Wetterich's “Universe without expansion” compared to standard cosmological redshift interpretation?

A recent news item in Nature promotes Wetterich's preprint "A Universe without expansion". All sounds very exciting but hard to judge for non-experts. As I understand from the Nature's article, the ...
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Why didn't we have inflation when the theory of everything and GUTS broke symmetry?

I asked this in astronomy and they suggested I ask it here. Inflation seems to have occurred when the symmetry breaking of the electroweak occurred. But do we know of any reason why we did not have ...
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Single field vs single clock inflation?

My question is very simple and short, but I couldn't find any explicit answer in papers and/or lecture notes. What is the difference between single field and single clock inflation? Or, maybe, what ...
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Can pre-inflationary gravitational attraction affect objects after inflation?

According to inflation theory, the inflation itself took place at some short yet finite time after Big Bang, so there should be some gravitational interactions present before inflation, some objects ...
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How can the universe be flat?

Okay, so I just want to clarify a few things. According to what I have read, we have measured the universe to be flat, and the shape of the universe is directly related to the mass-energy density. ...
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General questions related to inflation of the universe

(i) We know that the universe is expanding. As it expands, something has to "fill in", even if it is vacuum. Isn't energy required for this? For creating new "dark matter"? But we can't get energy ...
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By what process did the era of inflation end, or has it just slowed down (a lot)?

Could someone please explain the current model regarding: a) how the era of inflation was turned off (the graceful exit idea or alternatives)? b) what the timeline is between the era of inflation ...
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What's the difference between correlation functions and S-matrix, and between in-in formalism (or “closed time path formalism”) and in-out formalism?

I was reading the "in-in" formalism (or "closed time path formalism" used in condensed matter physics) in cosmology created by Schwinger in 1961, and there is a saying: "they care about correlation ...
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Was the expansion after the big bang faster than the speed of light? [duplicate]

I think it's called Planck time and it's the speed at which matter spread during the big bang. Was the big bang expansion faster than the speed of light?
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Structure formation: growth of density perturbations in sub-horizon vs super-horizon scales

I've always had difficulty visualizing how sub-horizon scales work versus super-horizon scales. Inflation causes perturbations due to quantum fluctuations. These are under-densities and over-...
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Need resource about super inflation in Loop Quantum Cosmology

In the current model during inflation H remains nearly constant where $ H = \frac{ \dot{a}}{a} $ but the scale factor a grows exponentially and requires a large number of e - folds N where $ N = ln\...
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Do we really need inflation for horizon problem?

This is a very fundamental doubt. I think i am missing something in inflation. The inflation theory solves the horizon problem by stating all of the universe started from a very small region in ...
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Cosmological fluctuations: what is gaussian?

When we are speaking about gaussianity and non-gaussianity in a cosmological context, what is gaussian or non-gaussian in the CMB? What would a non gaussian CMB look like compared to a gaussian one? ...
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What's the status of Cosmic Inflation after the BICEP2 debacle? [duplicate]

I've read that the gravitational waves supposedly discovered by the BICEP2 observatory last year (and touted as evidence for cosmic inflation) weren't actually gravitational waves, but some sort of ...
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Effective field theory of inflation in the slow roll case

I'm reading this set of notes by Daniel Baumann on the effective field theory of inflation but I can't quite understand one step in section 3.1.1 concerning slow roll inflation. Basically, the author ...
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Is there any limit on movement of space itself?

According to special relativity, c is the maximum speed at which all matter and information in the universe can travel. [IN SPACE] But the inflationary hypothesis says the space itself expanded ...
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Neutrinos born before inflation

What would happen, if there was (hypothetically, for any reason) a very large number of neutrinos+antineutrinos before the inflation period. They probably dont like to annihilate too much. I would ...