Universe: Einstein-DeSitter

Universe: Einstein-DeSitter

Published: February 14, 2008, 12:00 am
Updated: April 21, 2009, 8:43 pm
Lead Author: Sten Odenwald
Topics: Cosmology The Universe

Einstein's Initial Solution

In 1917, Albert Einstein tried to use his newly developed theory of general relativity to describe the shape and evolution of the universe. But what kind of universe should it be? There were an infinitude of mathematical solutions to Einstein's gravitational field equations, yet only one family of these could possibly represent our own universe. Which one?

The prevailing idea at the time was that the universe was static and unchanging so Einstein found a cosmological solution in which space had a closed, spherical geometry with matter uniformly filling it. To make such a universe static, so that it didn't change in time, the inexorable force of gravity pulling on every speck of matter had to be counteracted, otherwise such a universe would inevitably collapse under its own weight.

Cosmological Constant

Einstein's remedy for this dilemma was to add a new antigravity term to his original equations. It enabled his mathematical universe to appear as permanent and invariable as the real one. This term, usually written as an uppercase Greek letter Lambda, is called the Cosmological Constant, and has exactly the same value everywhere in the universe, delicately chosen to offset the tendency toward gravitational collapse at every point in space. Curiously, such a universe would be finite in space, possess matter, but the matter would not move. Like a snapshot frozen in time, all galaxies in the universe would be completely motionless relative to each other while at the same time the motion of their internal stars and gas clouds would occur unimpeded.

Willem de Sitter

The Dutch physicist Willem de Sitter (1872 - 1934) also looked for cosmological solutions to Einstein's equation for gravity and found not one but two solutions the same year. The first solution was Einstein's closed, static model with a carefully-tuned cosmological constant. This solution is often referred to as the "Einstein-de Sitter" model. But de Sitter also found a second solution in which there is no matter in the universe at all. The universe contained only the cosmological constant force itself. It is an utterly empty universe.

For billions of light years in any direction only darkness of the most unimaginable kind would meet your eye. Yet, in every cubic centimeter of this universe a mysterious force would be at work. Two test particles placed in this universe would find themselves eternally accelerating away from one another through the action of this force. Even without these test particles the separations between arbitrarily chosen pairs of points would increase exponentially with time. Whereas the Einstein-de Sitter model represented "matter without motion" the new de Sitter cosmology described the even stranger condition of "motion without matter".

After the announcement of the Einstein and de Sitter solutions in 1917, there were no further publications on relativistic cosmology until after the solar eclipse expeditions confirmed the bending of light by the sun in 1919.

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"Signals of a Strange Universe" - Eleven years ago results were first presented indicating that most of the energy in our universe is not in stars or galaxies but is tied to space itself. In the language of cosmologists, a large cosmological constant is directly implied by new distant supernovae observations. Suggestions of a cosmological constant (lambda) were not new — they have existed since the advent of modern relativistic cosmology. Such claims were not usually popular with astronomers, though, because lambda is so unlike known universe components, because lambda's value appeared limited by other observations, and because less-strange cosmologies without lambda had previously done well in explaining the data. What is noteworthy here is the seemingly direct and reliable method of the observations and the good reputations of the scientists conducting the investigations. Over the past eleven years, independent teams of astronomers have continued to accumulate data that appears to confirm the existence of dark energy and the unsettling result of a presently accelerating universe. The picture of a supernova that occurred in 1994 on the outskirts of a spiral galaxy was taken by one of these collaborations.  View full-size image.  (Source: NASA-Astronomy Picture of the Day, March 29, 2009. Credit: High-Z Supernova Search Team, HST, NASA.)

Citation

Odenwald, Sten, Ph.D. (Contributing Author); Bernard Haisch (Topic Editor). 2009. "Universe: Einstein-DeSitter." In: Encyclopedia of the Cosmos. Eds. Bernard Haisch and Joakim F. Lindblom (Redwood City, CA: Digital Universe Foundation). [First published February 14, 2008].
<http://www.cosmosportal.org/articles/view/138897/>

 

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