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 ...

learn more… | top users | synonyms (2)

0
votes
0answers
27 views

When did the strong force separate?

Given that Grand Unification may have happened, and inflation is accepted, which of these two scenarios is better accepted; 1) The strong force broke free before inflation, and is somehow causally ...
2
votes
1answer
331 views

Is the Universe Past-Eternal?

Does the Borde-Guth-Vilenkin theorem definitively demonstrate that the Universe cannot be past-eternal, whatsoever? Does it not assume a classical space-time while the real world requires Quantum ...
6
votes
1answer
257 views

Could the same symmetry be finetuning both the Higgs mass and the inflaton's interactions?

The observed Higgs boson mass is at an interesting place in parameter space, placing the standard model electroweak vacuum right at the edge of metastability. Among the proposed explanations of this ...
0
votes
1answer
34 views

How to calculate the scalar amplitude when two inflations happen successively?

Consider a single scalar field with some strange potential such that slow-roll inflation happens twice when it rolls down from the high potential point to the low potential point. In-between the two ...
1
vote
1answer
42 views

Hottest period in the history of the universe

Stack exchange's tagline is 'hot questions' - so here is one that will hopefully cause some heated debate. I remember hearing that the period immediately after inflation is theorized to be the ...
1
vote
1answer
40 views

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 ...
1
vote
1answer
225 views

Does Lyapunov exponent equate to exponential inflation?

Physics can be modeled by dynamical systems $f^t(x)$ as well as by PDEs. The most common dynamical system has hyperbolic fixed point and can be an attractor or a repellor. The dynamics at repellors ...
1
vote
1answer
164 views

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 ...
4
votes
2answers
881 views

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 ...
2
votes
1answer
168 views

What's the difference between eternal inflation and chaotic inflation?

Is there a real difference between eternal inflation and "chaotic inflation" theories?
2
votes
0answers
35 views

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 ...
1
vote
1answer
47 views

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 ...
5
votes
3answers
89 views

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 ...
1
vote
1answer
83 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 ...
1
vote
0answers
23 views

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. ...
1
vote
1answer
62 views

The CMB and the Hubble comoving radius

I have been thinking on this for a while and i don't get it. My point is, the comoving Hubble radius $(aH)^{-1}$ is the distance at wich the universe expansion begins to be superluminical. In an ...
3
votes
0answers
56 views

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 ...
0
votes
0answers
29 views

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 ...
2
votes
0answers
71 views

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 ...
1
vote
0answers
32 views

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 ...
0
votes
0answers
80 views

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 ...
1
vote
2answers
135 views

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 ...
0
votes
1answer
35 views

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 ...
4
votes
2answers
133 views

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 ...
1
vote
1answer
41 views

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 ...
12
votes
3answers
3k views

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?
1
vote
0answers
17 views

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 ...
2
votes
1answer
42 views

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 ...
7
votes
1answer
123 views

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 ...
0
votes
0answers
32 views

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 ...
5
votes
0answers
39 views

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 ...
0
votes
0answers
11 views

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 ...
1
vote
2answers
146 views

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 ...
0
votes
1answer
46 views

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 ...
0
votes
1answer
39 views

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?
4
votes
1answer
405 views

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 $$\boxed{\mathcal{L}=3a\left(k-\dot{a}^2\right)+a^3\left[\frac{1}{2}\dot\phi^2-V(\phi)\right]}$$ ...
0
votes
0answers
31 views

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 ...
1
vote
0answers
16 views

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 ...
0
votes
1answer
192 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 ...
5
votes
1answer
603 views

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 ...
1
vote
1answer
89 views

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 ...
0
votes
1answer
63 views

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 ...
1
vote
1answer
54 views

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 ...
0
votes
2answers
247 views

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. ...
0
votes
1answer
60 views

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 ...
5
votes
2answers
168 views

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 ...
2
votes
1answer
215 views

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 ...
0
votes
1answer
59 views

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?
1
vote
0answers
72 views

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 ...
0
votes
1answer
71 views

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 = ...