Big Bounce generic, Date and Hossain

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In summary, Ghanashyam Date and Golam Hossain have published a new paper in which they confirm that the Big Bounce is a generic occurrence in loop quantum cosmology (LQC), independent of quantizing ambiguities and details of scalar field dynamics. They also find that in a closed universe, the Big Crunch singularity is replaced by a bounce. This is seen as a significant step in the maturation of LQC as more researchers join in to corroborate and extend the original result by Martin Bojowald. The paper also explores consequences of LQC corrected cosmologies such as a mechanism for inflation, suppression of chaotic approach to singularity, and indication of a bounce at the Big Crunch singularity. These findings
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the Big Bounce is generic in LQC, say G.Date and G.Hossain
in a new paper http://arxiv.org/gr-qc/0407074 [Broken]

In LQC, as long as there is a scalar matter field, the bounce is
generic in the sense of being independent of
quantizing ambiguities and details of scalar field dynamics.

they also find that in a closed universe the Big Crunch singularity
goes away as well (in LQC) and is replaced generically by a bounce.

It looks to me like part of LQC coming of age---Bojowald got the
original result which zapped the Big Bang singularity and now more people
are joining in and corroborating and extending his result. these two
authors, as it happens, have found, or helped to find, a useful approximation of Bojo's original cosmological difference equation by a differential equation (see their equation 1) which looks nicer and neater than the difference equation especially in their choice of notation. More exactly, they have an "effective Hamiltonian" to approximate bojo's
original LQC Hamiltonian, and it looks as if they are milking that effective
Hamiltonian cow for all its worth. Both guys are of the smart young bunch of researchers that have gotten into Loop during the past few years
and right now they are in Chennai which looks like might become another center. So it is a "field maturation" paper, I think, as if people are finishing digging a tunnel thru the mountain and Bojo made a hole and saw some
sky thru it and other people help make the hole larger and after a while break out into the open daylight at the other end.

It is a short paper---the work looks good as far as I can tell. Here is an introductory paragraph exerpt

-----quote----
It has been long expected that the existence of singularity in the classical general relativity which has been shown to be quite generic thanks to the singularity theorems, will be removed when classical framework of gravity is extended to a quantum framework of gravity.

Despite of tremendous efforts made, unfortunately we still do not have a fully satisfactory theory of quantum gravity. In the las tcouple of decades two strong contenders have emerged: the string theory approach[1] and the loop quantum gravity (LQG) approach[2].

Theissueof fate of classical cosmological singularities has been addressed head-on within the LQG approach. More precisely, the adaptation of LQG methods to cosmological context, known as loop quantum cosmology (LQC) [3], has made impressive progress on the issue of singularities. It has been shown that the isotropic models (flat and closed)[4], and more generally the diagonal Bianchi class A models [5, 6], are free of singularity.

It is time now to explore further consequences of LQC corrected cosmologies.
---end quote---
 
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Another exerpt from Ghanashyam Date and Golam Hossain new paper

---quote---
Some of consequences of LQC corrected cosmologies have already been noted. First, there is a natural mechanism for inflation [7,8,9] within the context of isotropic models.

Secondly, for the Bianchi IX model there is a suppression of chaotic approach to singularity [10].

Thirdly, there is indication of a bounce at the big crunch singularity as well [11].

All of these have been explored within the framework of an effective Hamiltonian which incorporates the most significant non-perturbative corrections. These modifications stem from the non-trivial definition of the inverse triad operator in LQC[6, 12] which ensure that the matter density, spin connection components remain bounded as universe approaches zero volume.

---endquote---
 
  • #3


The Big Bounce is a concept that has been gaining attention in the field of quantum gravity, and this new paper by Date and Hossain adds to the growing body of evidence supporting its generality in loop quantum cosmology (LQC). The authors demonstrate that, in the presence of a scalar matter field, the bounce is independent of quantizing ambiguities and details of scalar field dynamics, making it a robust and generic feature in LQC. This result is in line with previous findings in the field, and further solidifies the idea of a Big Bounce as a viable alternative to the Big Bang singularity.

Furthermore, Date and Hossain's work also shows that in a closed universe, the Big Crunch singularity is replaced by a bounce, providing further evidence for the generality of this phenomenon. This paper is another step towards the maturation of LQC as a framework for studying cosmological singularities, and the authors' use of an effective Hamiltonian to approximate Bojowald's original LQC Hamiltonian is a promising development.

Overall, this paper adds to the growing body of research on the Big Bounce and its implications for our understanding of the early universe. It is a testament to the progress being made in the field of loop quantum gravity and the potential for LQC to provide insights into fundamental questions about the nature of space and time.
 

1. What is the Big Bounce theory?

The Big Bounce theory proposes that the universe goes through cycles of expansion and contraction, as opposed to the widely accepted theory of the Big Bang where the universe began from a single point of infinite density.

2. When was the Big Bounce theory first proposed?

The idea of the Big Bounce was first proposed in the 1920s by Belgian physicist Georges Lemaître, but it was further developed in the 1980s by physicist Roger Penrose and then by Paul Steinhardt and Neil Turok in the 2000s.

3. How does the Big Bounce theory explain the origins of the universe?

The Big Bounce theory suggests that the universe goes through an eternal cycle of expansion and contraction, with each cycle starting from a previous contraction. This means that the universe has no true beginning or end.

4. What evidence supports the Big Bounce theory?

Although there is no direct evidence for the Big Bounce, it is supported by mathematical models and calculations of the behavior of matter and energy in the universe. It also offers a potential explanation for the observed uniformity of the universe and the absence of an initial singularity.

5. How does the Big Bounce theory differ from the Big Bang theory?

The Big Bang theory suggests that the universe began from a single point in an explosion, while the Big Bounce theory proposes that the universe goes through cycles of expansion and contraction. Additionally, the Big Bounce theory does not have a singularity or a definite beginning, unlike the Big Bang theory.

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