The tag has no wiki summary.

learn more… | top users | synonyms (1)

1
vote
1answer
79 views

The gravity waves from the big bang? How can we know?

The latest news says that scientists detected gravitational waves from the Big Bang. My question is how do they know the waves originated in the big bang verses any number of supernovae and or ...
0
votes
1answer
19 views

Deriving the slow-roll parameter $\eta$

In inflationary theory, many papers start off by making the slow-roll approximation, on which many things depend. This approximation is usually presented by requiring that two 'slow-roll parameters' ...
2
votes
1answer
55 views

Universe inflation [duplicate]

Read in several publications that the Universe during a very short time (inflation), increased its size by a factor of $10^{50}$. What does it mean to increase the size of $10^{50}$ if you do not ...
3
votes
2answers
120 views

Cosmological constant doubts

I have read about cosmological constant given by einstein in universe in nutshell as well as in general and special relativity. But still I am not able to understand the aim to use it or to introduce ...
2
votes
0answers
16 views

Question on Equipartition at Reheating?

Apologies in advance if this is a silly question. I am fimiliar with the idea of Reheating in cosmology, as discussed briefly here. I have been reading several papers which make the assumption of ...
0
votes
1answer
111 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 ...
3
votes
1answer
40 views

'There shall be reheating' and other inflation-related questions [closed]

I've some basic questions about inflation: What is reheating exactly? What triggered the reheating? Is it something that one pulls out of a hat? Through which force did the decay of the inflation ...
0
votes
0answers
27 views

Understanding Bose enhancement in reheating

I'm struggling to understand the Bose enhancement in reheating. I've read that: At the end of inflation, the inflaton field, $\phi$, is something like a condensate with excitations of a single ...
1
vote
3answers
100 views

Is the universe flat?

There are more than one way to view the description of the universe as flat. There is the description of an open, flat or closed universe in terms of it's fate, expansion forever away from gravity, or ...
0
votes
1answer
33 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 ...
0
votes
1answer
24 views

Is redshift the only way by which we can tell that space is expanding?

There's another question on physics.SE whose answer, if I have understood it correctly, explains that the farther the points are in space the faster they are moving away from each other. Actually, ...
7
votes
1answer
102 views

In the B mode power spectrum, what is the relationship between the multipole number and the wavelength of the seed gravitational waves?

One of the key datasets of the recent BICEP2 results is the B mode power spectrum shown below. The existence of these B modes implies the existence of gravitational waves prior to inflation. My ...
0
votes
1answer
19 views

Inflation in a closed universe or a stage 1 multiverse?

With the discovery of gravitational waves, Max Tegmark has been using this promote his level 1 multiverse in that the universe is flat and everything duplicates. My question is, are there any ...
3
votes
1answer
72 views

Does inflation predict a multiverse?

Does inflation necessarily predict a multiverse? Or is it the case that "It all depends on the properties of the initial field responsible for inflation, about which we can only speculate"?
0
votes
1answer
50 views

What is the mass of the universe?

Working with a flat and infinite model of the universe (which seems to be the most popular serious model these days), the density of the universe is 3e-28 kg/m^3 [1]. When added to the cosmological ...
3
votes
1answer
65 views

What is $\phi$ as refered to in Guth 2007?

In this 2007 paper by Alan Guth discussing eternal cosmic inflation, he start's using a value $\phi$ on page 8. My understanding is that $\phi$ is the scalar field representing the dark energy of a ...
15
votes
2answers
1k views

Inflation and the Meaning of Time

I'm not quite sure how to ask this so that it can be answered in layman's terms, but I have lately seen, in several places, that with cosmological inflation, there was a point where the universe ...
-4
votes
1answer
143 views

Is the interpretation of BICEP2 data being due to “graviational waves” concerning considering the negative results of the LIGO's experiments? [closed]

Gravitational waves are a yet unproven idea... The lack of positive results from LIGO indicates these are still theoretical constructs not yet supported by experimental data. Is not the explanation of ...
2
votes
1answer
95 views

Difference between horizon and flatness problems & how inflation solves flatness (w/out math)

Laymen here so I'm hoping for an answer for my query that doesn't involve math. I'm reading about inflation and how it solves the flatness and horizon problems. I get that the horizon problem deals ...
9
votes
4answers
4k views

Size of universe after inflation?

Wikipedia states the period of inflation was from $10^{-36}$sec to around $10^{-33}$sec or $10^{-32}$sec after Big Bang, but it doesn't say what the size of the universe was when inflation ended. ...
7
votes
1answer
650 views

On Flatness problem, Inflation etc

I have a couple of naive questions from the topic of the title. We know \begin{eqnarray} \Omega-1=\frac{k}{a^2H^2}-\frac{\Lambda}{3H^2} \end{eqnarray} Now I read that from the standard big bang ...
66
votes
5answers
5k views

What was the major discovery on gravitational waves made March 17th, 2014, in the BICEP2 experiment?

The Harvard-Smithsonian Centre for Astrophysics held a press conference today to announce a major discovery relating to gravitational waves. What was their announcement, and what are the implications? ...
6
votes
1answer
181 views

The BICEP2 data are evidence of gravitational waves and of inflation. Are they also the first observation that requires quantum gravity?

It strikes me that the recent announcement of data from BICEP2 contains two really Big Deals: the first evidence of gravitational waves the first evidence of inflation. Is there also a third? ...
10
votes
2answers
581 views

Can the Big Rip really rip apart an atomic nucleus?

Some scenarios describing the fate of the matter vs dark energy tug of war on the universe involve the acceleration of the universe increasing to the point that it ends up ripping apart even atoms. ...
3
votes
2answers
146 views

BICEP2 experiments

How was the polarization experimentally measured in the BICEP2 experiments and why did they look specifically at B-modes? Why is it implying the existence of gravitational waves and the need to ...
0
votes
2answers
76 views

Size of Universe after inflation

I read in some website that during the period of inflation, the expansion of the universe underwent incredibly fast, and its size increased by a factor of $10 ^{50}$, see this link In this field, I ...
9
votes
1answer
111 views

BICEP2 and e-foldings during inflation

After the BICEP2 results, we now know that $n_s = 0.96$ and $r = 0.2$. From what I understand, this fits extremely well with the basic chaotic inflation model given by $V(\Phi) = \lambda \Phi^4$. We ...
9
votes
1answer
130 views

What's the $\ell$ in the Bicep2 paper mean?

The BICEP experiment's recent announcement included the preprint of their paper, BICEP2 I: Detection of $B$-mode polarization at degree angular scales. BICEP2 Collaboration. To be submitted. ...
5
votes
1answer
208 views

What do the BICEP2 results mean for string gas cosmology and the ekpyrotic universe?

The imprint of gravitational waves created shortly after the big bang may offer direct evidence for inflation theory, according to a discovery by the BICEP2 experiment at the South Pole and released ...
3
votes
1answer
141 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 $$\boxed{\mathcal{L}=3a\left(k-\dot{a}^2\right)+a^3\left[\frac{1}{2}\dot\phi^2-V(\phi)\right]}$$ ...
3
votes
1answer
99 views

How big of an area of the sky is the BICEP2 survey?

So here is the BICEP2 picture: How big is that? How much of the sky? Say, compared to this picture of the CMB by Planck:
5
votes
2answers
236 views

What experiments compete with BICEP 2, and when are their results expected?

The recent results of the BICEP 2 experiment published on March 17th 2014, has generated a lot of media attention, with the general consensus being that "this is a major discovery" perhaps leading to ...
1
vote
1answer
38 views

Is Λ-CDM and no inflaton field compatible with the observed value of the scalar spectral index?

From the cosmic microwave background, one can extract the scalar spectral index $n_s$. It is measured to be smaller than 1 by several standard deviations. Wikipedia says that it is a parameter of the ...
2
votes
0answers
223 views

BICEP2 and string theory

Can anybody elaborate on the implications of the BICEP2 result for string theory? The discussion here What experiment would disprove string theory? suggests that refuting string theory is rather ...
3
votes
0answers
82 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 ...
1
vote
0answers
49 views

Object that causes spacetime to expand?

Is there any thing that will cause spacetime to expand, so that particles are pushed away from them rather than pulled towards it. I know things such as black holes and planets causes dips and curve ...
2
votes
0answers
31 views

Is brane world scenario in contrast with inflation theory? [closed]

Is brane world scenario in contrast in some way with inflation theory ?
1
vote
1answer
54 views

How many years of expansion occurred during inflation?

During inflation, expansion happens at a very rapid rate. How many years of expansion did it fast forward through? Meaning, if it weren't for inflation, how many years would it take for the ...
5
votes
2answers
144 views

What is the meaning of the “expansion of space”?

When we say that "the space between galaxies is expanding," what do we really mean? For instance, if I think of space as being a Cartesian grid, then when space expands should I think of it as adding ...
1
vote
1answer
59 views

Expanding Universe now and $\sim14$Gyr ago

All know that Inflation may solve some of the problems of the Standard Model of Cosmology and today we suppose that the field responsible for that is the inflaton. The properties of the potential ...
2
votes
2answers
183 views

Is inflation deterministic?

In some theories inflation is supposed to be able to turn quantum fluctuations into macroscopic inhomogeneities. I don't understand how an isolated system such as the universe can undergo such a ...
1
vote
0answers
52 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 ...
5
votes
2answers
589 views

Planck satellite 2013 results impact on cosmological models

I've recently watched a "Through the Wormhole" episode from 2010 named "What Happened Before the Beginning?", where cyclic and ekpyrotic cosmological models are explained. In this episode the creators ...
11
votes
2answers
498 views

How is it possible the universe expanded faster than the speed of light during inflation?

In a documentary written in collaboration with Stephen Hawking, the narrator (supposedly Stephen Hawkings) says that by the time the cosmos was 10 minutes old, it had already expanded thousands of ...
6
votes
0answers
185 views

Equation of motion for cyclic model of the universe

I recently started to study about cyclic universe. I came across this article [1]. My question is about the action that used for describing the cyclic model: $$S = \int d^{4}x\sqrt{-g}(\frac{1}{16\pi ...
0
votes
1answer
229 views

If the unobservable universe is not “open” and will collapse, would we be able to tell?

Assuming hypothetically that it happens now while we are alive and analyzing our observable universe. If the unobservable universe collapses in a "Big Crunch", will we see its effects in our ...
2
votes
0answers
62 views

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

Is there a real difference between eternal inflation and "chaotic inflation" theories?
6
votes
4answers
538 views

de sitter cosmologic limit

It has been said that our universe is going to eventually become a de sitter universe. Expansion will accelerate until their relative speed become higher than the speed of light. So i want to ...
11
votes
2answers
283 views

How is causal patch complementarity compatible with behavior during inflation?

Causal patch complementarity is the conjecture that in de Sitter space with a positive cosmological constant, the states within the causal patch are sufficient to fully describe the universe with the ...
0
votes
0answers
56 views

Does the Holographic Principle disagree with the eternal inflation model?

Does the Holographic Principle disagree with the eternal inflation model or it's just a new way to study quantum gravity?