New Guth paper-reviewing by-now-familiar scenario

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In summary, Guth's paper discusses the concept of eternal inflation and its implications for our universe. He explains the mechanisms that lead to eternal inflation and the challenges in defining probabilities in an eternally inflating spacetime. He also argues that while inflation is eternal into the future, it is not eternal into the past and requires some additional physics to describe the past boundary of the inflating region. The possibility of an upper bound for when inflation started is also discussed, with the conclusion that it depends on the quantum gravity model being used.
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marcus

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new Guth paper--reviewing by-now-familiar scenario

http://arxiv.org/abs/hep-th/0702178
Eternal inflation and its implications
Alan H. Guth
21 pages, 5 figures. Talk presented at the "2nd International Conference on Quantum Theories and Renormalization Group in Gravity and Cosmology (IRGAC 2006)," Barcelona, Spain, 11-15 July 2006, to be published in J. Phys. A

"I summarize the arguments that strongly suggest that our universe is the product of inflation. The mechanisms that lead to eternal inflation in both new and chaotic models are described. Although the infinity of pocket universes produced by eternal inflation are unobservable, it is argued that eternal inflation has real consequences in terms of the way that predictions are extracted from theoretical models. The ambiguities in defining probabilities in eternally inflating spacetimes are reviewed, with emphasis on the youngness paradox that results from a synchronous gauge regularization technique. Although inflation is generically eternal into the future, it is not eternal into the past: it can be proven under reasonable assumptions that the inflating region must be incomplete in past directions, so some physics other than inflation is needed to describe the past boundary of the inflating region."
 
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marcus said:
Although inflation is generically eternal into the future, it is not eternal into the past: it can be proven under reasonable assumptions that the inflating region must be incomplete in past directions, so some physics other than inflation is needed to describe the past boundary of the inflating region."

Even if the calculated past is not eternal (as calculated by some method) is there any possible way of having an upper bound defined at which inflation started?

If no such upper bound can be given, it means inflation did not have to start somewhere in the past.
 
  • #3
heusdens said:
.. is there any possible way of having an upper bound defined at which inflation started?
..

Yes. what one calculates depends on the QG model one uses.

If one uses LQC then the model evolves deterministically back in time, through the epoch where the classical singularity was, into an epoch of gravitational collapse.

In this model, inflation starts at the time of the bounce: that is, about 14 billion years ago.

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To clarify: I didn't post Guth's abstract because I think his ideas are reasonable or persuasive. Personally I don't find 'eternal inflation' very convincing.
It's as if some people---Guth, Linde---got one good idea 30 years ago and can't stop talking about it, so it gets kind of magnified in importance, for them.
I posted the abstract because some people DO find eternal inflation, bubbles etc etc, appealing so that a new Guth paper about it could be of interest to them.
 

1. What is the "New Guth paper" and what scenario does it review?

The "New Guth paper" refers to a recent scientific paper written by physicist Alan Guth, known for his work on the theory of cosmic inflation. The paper reviews the "by-now-familiar scenario" of cosmic inflation, which is a theory that explains the rapid expansion of the universe in its early stages.

2. What is the significance of the "New Guth paper" in the field of cosmology?

The "New Guth paper" has generated a lot of buzz in the field of cosmology as it presents new insights and challenges to the current understanding of cosmic inflation. It has sparked further discussions and research into this important theory of the origins of the universe.

3. What are some key points discussed in the "New Guth paper"?

The "New Guth paper" discusses several key points, including the possibility of a multiverse, the role of dark energy in cosmic inflation, and the limitations of the current understanding of inflation. It also proposes new ideas and scenarios to address these issues.

4. How does the "New Guth paper" contribute to the existing body of knowledge on cosmic inflation?

The "New Guth paper" adds new insights and perspectives to the existing body of knowledge on cosmic inflation. It offers alternative explanations and potential solutions to some of the current challenges and limitations of this theory.

5. What are the implications of the "New Guth paper" for future research in cosmology?

The "New Guth paper" has opened up new avenues for research in cosmology, particularly in the study of cosmic inflation. It has also sparked debates and discussions among scientists, leading to further investigations and potential breakthroughs in our understanding of the origins and evolution of the universe.

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