Universe: Friedman

Universe: Friedman

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

Friedmann's Foundation

The Einstein-de Sitter, and de Sitter cosmologies with their non-zero cosmological constants remained unchallenged until 1922 when the Russian mathematician Alexander Friedmann (1888 - 1925) began producing a whole new class of cosmological models based on Einstein's equations but without the extra cosmological constant term added. Einstein wasn't impressed. In an unpublished comment to Friedmann's paper, Einstein writes,

"Friedmann's paper, while mathematically correct is of no physical significance."

It's not that Einstein was a bad sport but most likely that the notion of a motionless universe was too overpowering to ignore. Look outside your window at the night sky and observe that nothing moves.

Friedmann started with Einstein's original equation for gravity and discovered a family of non-static cosmological models. He published his 1922 paper, "On the Curvature of Space," in a distinguished german journal. Unfortunately it received little notice. In 1925, Friedmann died prematurely before he ever knew of the lasting changes in cosmological theory that his work had wrought.

Lemaitre – Expanding Universe Model

Then a few years later in 1927, Georges Lemaitre (1894 - 1966), a Belgian mathematician and ordained priest, published a paper, "A Homogeneous Universe...Accounting for the Radial Velocity of Extra Galactic nebula" which also drew little attention until Sir Arthur Eddington arranged to have it translated and published in the Monthly Notices of the Royal Astronomical Society some four years later. Lemaitre had discovered an expanding universe model based on Einstein's cosmological constant solution. He also tied this model to Edwin Hubbel's discovery of a velocity-distance law for galaxies by showing that these expanding universe models all predict such a 'Hubble Law' for any observer.

Lemaitre went far beyond merely toying with abstract mathematical solutions for the global shape of spacetime and actually added a completely new feature to the discussion of cosmology never before seriously considered by astronomers. Lemaitre proposed that the universe began as a single lump of matter, a primeval atom, that radioactively decayed in an outrushing explosion. This is why Lemaitre is often called the "Father of the Big Bang."

Eddington-Lemaitre Models

By 1932 Sir Arthur Eddington showed that all models that employ a cosmological constant are unstable and lead to expansion, so Einstein's original motivation for introducing such a parameter was no longer viable. The universe might seem stable and frozen in time, but this condition was an extremely delicate one to create or maintain for eternity. He further developed the Lemaitre model into a more detailed theory which is why these are sometimes called the Eddington-Lemaitre models.

Admitting his blunder, and no doubt kicking himself for having missed a golden opportunity to be the "Father of the Universe," Einstein retracted the theoretical need for Lambda (cosmological constant) in 1932. Howard Robertson and Arthur Walker also demonstrated by 1935 that a spacetime defined by the metric obtained by assuming matter was distributed uniformly throughout the universe had another interesting property. It could be sliced into 3-D space sections with a single Cosmic Time common to all observers located on each of the space sections. What this meant was that all observers would exactly agree when the universe was born in terms of their own local clocks.

Today, these cosmological models are referred to by their formal names as the Friedmann-Robertson-Walker (FRW) or the Friedmann-Lemaitre- Robertson-Walker (FLRW) models. Of course it was Fred Hoyle, the irrascable co-inventor of the competing Steady State model who in 1955 actually gave FRW cosmologies their popular name: Big Bang Cosmology. In 1993, the editors of "Sky and Telescope" magazine sponsored a public contest to re-name Big Bang something less pejorative. They received thousands of suggestions, but were unable to come up with one that could replace the evocative name given to it by its foremost opponent. In politics, it is often the critics that get to nickname an idea. The more academic-sounding Supply-side Economic Theory quickly became Trickle-down Economics and even Voodoo Economics by its detractors, and it is often these later incarnations that we remember. In scientific circles, however, it is almost unheard of that the honor of nicknaming a theory doesn't reside with its creators. This is why 'Big Bang Theory' has such a ludicrous sound to it despite the fact that it is the premier theory of cosmology of this century.

Related EoC Articles

External Links

Preview Image

Russian mathematician and physicists Alexander Alexandrovich Friedman, or Friedmann, or Frieadmann (in Finnish Aleksandr Fridman). (Source: Wikipedia.)

Citation

Odenwald, Sten, Ph.D. (Contributing Author); Bernard Haisch (Topic Editor). 2009. "Universe: Friedman." 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/138899/>

 

Add Comment

Comments

There are no comments.

Add Comment



You must be logged in to post a comment. Click here to login.