Open Questions: Cosmological Models

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See also: Cosmic inflation -- M-theory -- Quantum cosmology

Introduction

The inflationary multiverse

Chaotic inflation

Eternal inflation

Cyclic/ekpyrotic cosmology

The landscape


Recommended references: Web sites

Recommended references: Magazine/journal articles

Recommended references: Books

Introduction

Why should the universe be unique? Why should there be just one universe?

Those seem, at first glance, like strange questions, if by "universe" we mean "everything there is". However, if instead we mean simply "everything we can possibly observe with our current technology", then the questions aren't so unreasonable. In fact, they are rather intriguing.


Recommended references: Web sites

Site indexes


Sites with general resources

Paul J. Steinhardt
Personal Web site. Steinhardt is one of the main proponents of the "cyclic universe" cosmology. The site contains a number of articles and papers on the subject. There are also articles on other topics in cosmology, such as dark matter, dark energy, and quintessence.


Surveys, overviews, tutorials

Multiverse
Article from Wikipedia. See also Parallel universe.
Loop Quantum Cosmology
Detailed article by Martin Bojowald in Living Reviews in Relativity.
Which mathematical structure is isomorphic to our universe?
In spite of the title and the "theory of everything" reference, the topic here is multiple universes. The page introduces a technical article by Max Tegmark, entitled Is "the theory of everything" merely the ultimate ensemble theory? (PDF format).
Parallel Universes
Introduction to a technical paper of the same title, by Max Tegmark. Four levels of the concept of "multiple universes" are discussed. There is also a list of frequently asked questions stimulated by the article.
My So-Called Universe
Interesting but brief examination of philosophical arguments for and against multiple universes, by Jim Holt.
Surveying the Landscape
December 2005 article from Seed Magazine, consisting mostly of brief quotes from cosmologists about the idea of "The Landscape".
Are There Other Universes?
February 2002 article from Space.com. Discusses theories of "parallel" universes and whether or not the theories can be tested.
'Brane-Storm' Challenges Part of Big Bang Theory
April 2001 article from Space.com. Discusses Paul Steinhardt's "ekpyrotic" theory.
The Structure of the Multiverse
Technical paper by David Deutsch. "The structure of the multiverse is determined by information flow. "
The Endless Universe: A Brief Introduction to the Cyclic Universe
November 2001 overview paper by Paul Steinhardt. A slightly later (May 2002) paper by Steinhardt on this model is here.
A Brief Introduction to the Ekpyrotic Universe
Brief overview by Paul Steinhardt.
Cyclic model FAQs
Questions and answers concerning the cyclib model, by Paul Steinhardt.
Echoes from Before the Big Bang May Be Inaudible
July 2007 Scientific American article, subtitled "New theory calls into question whether we'll ever know what the universe was like before the big bang."
A Recycled Universe
February 2002 Scientific American In Depth article, subtitled, "Crashing branes and cosmic acceleration may power an infinite cycle in which our universe is but a phase."
Colliding Branes and the Origin of the Hot Big Bang
Slide presentation on his ekpyrotic universe theory, by Paul Steinhardt, at the 2001: A Spacetime Odyssey conference.
Inflationary Theory versus Ekpyrotic/Cyclic Scenario
Technical paper by Andrei Linde, which argues that the ekpyrotic/cyclic cosmology, as originally proposed, does not solve any of the major cosmological problems, such as the flatness and entropy problems. A modification is suggested which simplifies the scenario, solves the problems, and produces a theory equivalent to the usual chaotic inflation scenario.


Recommended references: Magazine/journal articles

Big Bang or Big Bounce?: New Theory on the Universe's Birth
Martin Bojowald
Scientific American, October 2008
When worlds collide
Diana Steele
Science News, June 7, 2008
The Myth of the Beginning of Time
Gabriele Veneziano
Scientific American, May 2004
When Branes Collide
Steve Nadis
Astronomy, May 2002, pp. 34-39
The so-called "ekpyrotic theory" may offer an alternative to inflation as a scenario for the earliest moments of the universe. The idea is based on M-theory -- the latest version of superstring theory -- and suggests that the universe as we know it originated in the collision of two parallel 5-dimensional M-theory objects known as "branes".
When Branes Collide
Ron Cowen
Science News, September 22, 2001, pp. 184-186
A new theory of the origin of the universe might explain everything that the inflationary big bang theory does, but also have a closer relation to superstring theory.


Recommended references: Books

Martin Rees -- Our Cosmic Habitat
Princeton University Press, 2001
Rees, Great Britain's Astronomer Royal has written a number of books on cosmology for a general audience. This is another, which once again surveys basic concepts of cosmology and the big bang. Some of his recent books have considered the interesting fact that certain aspects of our universe seem to be uniquely adapted to allow the existence of sentient life. The most natural explanation for this is the existence of innumerable universes with hugely varying characteristics, out of which only a very small number have (like our universe) the necessary very special properties that allow life.

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Copyright © 2002 by Charles Daney, All Rights Reserved