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For 300 years Newton's Universal Law of Gravitation was adequate to explain the observed movements of heavenly bodies. The image of space and matter Newton conjured lasted until the early 20th century when Einstein proposed his Special and General Theories of Relativity . In order to match the observed static universe Einstein added a term called the Cosmological Constant to the equation. He later called this his "biggest blunder". In the 1920's Edwin Hubble discovered the universe was expanding. This brought forth the big bang theory which a lot of people found unnerving at first. Until that time, people had assumed the universe was more or less static. Einstein's General Theory of Gravitation suggested three general models of the universe [Closed, Flat and Open] were possible, depending upon the total mass of the universe.

Throughout the 20th century observational techniques improved and more data filled in the picture. [CMB, WMAP, COBE, Boomerang, LIGO] A variety of bizarre objects such as black holes, neutron stars, quasars and galactic clusters were detected. At the same time, a zoo of subatomic particles was being uncovered. A Standard Model (see also), (see also) of the constituents and interactions of matter was developed. In the 1970s the theory of quantum chromodynamics described the strong force, one of the four known fundamental forces . In 1981 Alan Guth proposed a modification of the Big Bang theory called Inflation. This theory explained some features of the Cosmic Microwave Background CMB . Another significant theory, of several variants, which shows much promise is string theory .

It is curious that the quest to understand the structure of the universe is proceeding simultaneously on the smallest and the largest scales, ranging from the constituents of the atom to galactic clusters.

In the last three decades of the century astronomers realized that there was not enough mass of the ordinary sort to explain the motions of galaxies. They called the missing mass Dark Matter. and started a search. There is no currently accepted theory explaining Dark Matter. In 1998, astronomers made the astounding discovery that the rate of expansion of the universe was increasing. Scientists did not have any theoretical reason why this should be so. This missing energy they called Dark Energy. There is no currently accepted theory explaining Dark Energy. Some people think it may be some form of Cosmological Constant; others a form of quantum vaccum energy.

Cosmology is currently in ferment . Nobody is quite sure just which observations are correct. The evidence from Supernovae seem to indicate one thing, while the evidence from the large scale structure of the universe indicates another. Finer and finer measurements of the CMB are being undertaken. It may be that one or more of these observations is in error. There are several fundamental questions up in the air.

How did the universe begin?
What is the total mass of the universe?
How many dimensions are there?
Why is time directional?
Was there time before the big bang?
How many fundamental forces are there?
Are the four known forces manifestations of a single unified force?
How can gravity be reconciled with quantum theory?
Are gravitons real?
What is Dark Energy?
What is Dark Matter?
What particles make up Dark Matter?
How and why do neutrinos change their identity as they travel?
Are there other particles like the Higgs boson?
Are there other particles in general?
Why does there seem to be more matter than antimatter?
Why is the expansion of the universe accelerating?
What will be the Fate of the Cosmos?
Is the proton stable?
There are dozens of new theories being proposed. They all make predictions which need to be checked. There is every possibility that a major new theory will arise from this ferment. It is a very exciting time.

What follows is a few sites with further information about the current work in cosmology, some mainstream news reports, then a few of the papers detailing the theories and observations. First a quote to put you in the appropriate frame of mind:

"In the late 1960s a young assistant professor at Columbia University, named Edward P. Tryon attended a seminar given by Dennis Sciama, a noted British cosmologist. During a pause in the lecture, Tryon threw out the suggestion that 'maybe the universe is a vacuum fluctuation.' Tryon intended the suggestion seriously, and was disappointed when his senior colleagues took it as a clever joke and broke into laughter."
-Alan Guth, The Inflationary Universe, page 12

Last modified April 2, 2014