Showing papers by "Alan H. Guth published in 2003"
TL;DR: A simple kinematical argument is offered that a cosmological model which is inflating--or just expanding sufficiently fast--must be incomplete in null and timelike past directions, and a bound on the integral of the Hubble parameter over a past-directed timelikes or null geodesic is obtained.
Abstract: Many inflating spacetimes are likely to violate the weak energy condition, a key assumption of singularity theorems. Here we offer a simple kinematical argument, requiring no energy condition, that a cosmological model which is inflating---or just expanding sufficiently fast---must be incomplete in null and timelike past directions. Specifically, we obtain a bound on the integral of the Hubble parameter over a past-directed timelike or null geodesic. Thus inflationary models require physics other than inflation to describe the past boundary of the inflating region of spacetime.
566 citations
Posted Content•
TL;DR: A discussion of the early development of the theory of inflationary density perturbations was conducted at Stephen Hawking's 60th birthday conference as mentioned in this paper, where the authors presented a graph of the probability distribution for the time of last scattering for CMB photons, and summarized the recent observational successes of these predictions.
Abstract: This talk, which was presented at Stephen Hawking's 60th birthday conference, begins with a discussion of the early development of the theory of inflationary density perturbations. Stephen played a crucial role in this work, at every level. Much of the foundation for this work was laid by Stephen's 1966 paper on cosmological density perturbations, and by his 1977 paper with Gary Gibbons on quantum field theory in de Sitter space. Stephen was a major participant in the new work, and he was also a co-organizer of the 1982 Nuffield Workshop, where divergent ideas about inflationary density perturbations were thrashed about until a consensus emerged. In the second part of the talk I summarize the recent observational successes of these predictions, I present a graph of the probability distribution for the time of last scattering for CMB photons, and I summarize a recent theorem by Borde, Vilenkin, and me which shows that although inflation is generically eternal to the future, an inflationary region of spacetime must be incomplete in null and timelike past directions.
19 citations
01 Nov 2003
TL;DR: A discussion of the early development of the theory of inflationary density perturbations was conducted at Stephen Hawking's 60th birthday conference as discussed by the authors, where the authors presented a graph of the probability distribution for the time of last scattering for CMB photons, and summarized the recent observational successes of these predictions.
Abstract: This talk, which was presented at Stephen Hawking's 60th birthday conference, begins with a discussion of the early development of the theory of inflationary density perturbations. Stephen played a crucial role in this work, at every level. Much of the foundation for this work was laid by Stephen's 1966 paper on cosmological density perturbations, and by his 1977 paper with Gary Gibbons on quantum field theory in de Sitter space. Stephen was a major participant in the new work, and he was also a co-organizer of the 1982 Nuffield Workshop, where divergent ideas about inflationary density perturbations were thrashed about until a consensus emerged. In the second part of the talk I summarize the recent observational successes of these predictions, I present a graph of the probability distribution for the time of last scattering for CMB photons, and I summarize a recent theorem by Borde, Vilenkin, and me which shows that although inflation is generically eternal to the future, an inflationary region of spacetime must be incomplete in null and timelike past directions.
11 citations
13 Jan 2003
TL;DR: The history of time since the beginning of the universe has been discussed in this article, with a focus on how and when the universe evolved from an infinite tree of inflationary spacetime.
Abstract: While there is no consensus about the history of time since the beginning, in this paper I will discuss some possibilities. We have a pretty clear picture of cosmic history from the electroweak phase transition through the time of recombination, a period which includes the QCD phase transition and big bang nucleosynthesis. This paper includes a quantitative discussion of the age of the universe, of the radiation-matter transition, and of hydrogen recombination. There is much evidence that at earlier times the universe underwent inflation, but the details of how and when inflation happened are still far from certain. There is even more uncertainty about what happened before inflation, and how inflation began. I will describe the possibility of ``eternal'' inflation, which proposes that our universe evolved from an infinite tree of inflationary spacetime. Most likely, however, inflation can be eternal only into the future, but still must have a beginning.
4 citations
01 Jan 2003
TL;DR: The history of time since the beginning of the universe has been discussed in this article, with a focus on how and when the universe evolved from an infinite tree of inflationary spacetime.
Abstract: While there is no consensus about the history of time since the beginning, in this paper I will discuss some possibilities. We have a pretty clear picture of cosmic history from the electroweak phase transition through the time of recombination, a period which includes the QCD phase transition and big bang nucleosynthesis. This paper includes a quantitative discussion of the age of the universe, of the radiation-matter transition, and of hydrogen recombination. There is much evidence that at earlier times the universe underwent inflation, but the details of how and when inflation happened are still far from certain. There is even more uncertainty about what happened before inflation, and how inflation began. I will describe the possibility of ``eternal'' inflation, which proposes that our universe evolved from an infinite tree of inflationary spacetime. Most likely, however, inflation can be eternal only into the future, but still must have a beginning.
1 citations