Universe: Hot Big Bang

April 21, 2009, 8:44 pm
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Introduction

In the Gamow, Alpher and Fermi theory of the expanding universe ca 1948, the universe started out in a hot, dense state. Conditions were changing rapidly as the universe expanded so that temperatures and densities were falling. There was no equilibrium condition that could be sustainable for too long. Temperatures were in the billions of degrees. There was a mixture of neutrons, protons and electrons that existed by about 13 minutes after the expansion had started. Gamow called this matter 'ylem' after a Webster's Dictionary entry that identified this as an archaic term meaning "the first substance from which the elements were supposed to be made."

A variation on Big Bang cosmology is Brans-Dicke cosmology which is based on a modification to Einstein's general relativity in which a 'scalar field' is added to the usual spacetime metric representing the gravitational field. This 'scalar-tensor' theory of gravity is not supported by careful investigations of general relativity because it requires that gravitational forces change slowly over billions of years. The cosmological implications of Brans-Dicke theory would have their strongest impact on the expansion rate of the universe which would depend not just on time, but on a second physical parameter that depends on the strength of this new scalar field. There would still exist an initial singularity of the kind predicted by Big Bang cosmology.

"We assume that the universe expands from a highly condensed state. It is possible that in the intense gravitational field of this condensed state, matter is created [but] in our view of our present state of ignorance, there seems to be little point in speculating about the process involved. In any case, the creation process lies outside the present [Brans-Dicke] theory.."

Although the initial temperature of the Big Bang is believed to be somewhere near the Planck Temperature of 1032 K, in 1969 Hagedorn proposed that by a temperature of a few trillion degrees, the Big Bang saturates and ceases to grow hotter at earlier times. What happens is that the energy that would have gone into thermal motion goes into creating more and more exotic particles without limit. This quenches the primeval temperature increase as we look back to earlier epochs.

In all of the Big Bang cosmological models spawned by the Friedman solutions to Einstein's equation for gravity, a peculiar state called a "Singularity" is absolutely demanded. This condition occurs at the time of the Big Bang and represents a state in which the curvature of spacetime becomes infinite. This also means that temperature and density also become infinite. Steven Hawking and Roger Penrose developed a powerful set of theorems in the early 1970's that proved that this condition is absolutely unavoidable in homogeneous universes such as our own. All world lines terminate on the initial spacetime Singularity. Every scrap of matter in the universe can be traced back in time to its emergence from this state of lethal curvature, and in the future if our universe is destined to re-collapse, a similar condition will be unavoidable.

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External Links

  • Cosmic Background Explorer (COBE) - Developed by NASA's Goddard Space Flight Center to measure the diffuse infrared and microwave radiation from the early universe to the limits set by our astrophysical environment. NASA.
  • Wilkinson Microwave Anisotropy Probe (WMAP) - A NASA Explorer mission that launched June, 2001 to make fundamental measurements of cosmology – the study of the properties of our universe as a whole. WMAP has been stunningly successful, producing our new Standard Model of Cosmology. WMAP continues to collect high quality scientific data. NASA.

Preview Image

Artists' concept of the initial "big bang." (Source: NASA.)

Citation

Odenwald, Sten, Ph.D. (Contributing Author); Bernard Haisch (Topic Editor). 2009. "Universe: Hot Big Bang." In: Encyclopedia of the Cosmos. Eds. Bernard Haisch and Joakim F. Lindblom (Redwood City, CA: Digital Universe Foundation). [First published January 13, 2008].
<http://www.cosmosportal.org/articles/view/138901/>

 

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Citation

(2009). Universe: Hot Big Bang. Retrieved from http://www.cosmosportal.org/view/article/138901

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