WILLIAM & DEBORAH HILLYARD
Astronomy & Cosmology

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The End of the Universe

The theories discussed below have appeared at varying times through the 20th, and into the 21st, centuries.  Some earlier theories, based on the information that was available at the time, are now seen to be unlikely.  I have included some of them for completeness.  Current evidence of the rate of expansion of the Universe, and calculations of the mass density, imply that the most likely scenario is a "Big Freeze", often called the "heat Death of the Universe".  However, new theories of cyclic or oscillating universes are avoiding many of the earlier problems, like entropy, and may well prevail.  The "how, or if, the Universe started" question is intimately linked to "how, or if, the Universe will end".  Do read the sections on the "early Universe" and alternative theories to the Big Bang before looking at this section. 

Introduction

There are two features of the Universe that are key to understanding its fate; they are its density and its shape.  There is also the Critical Density which is the density the Universe would have to have to be flat.  The Greek letter Omega (      ) is used to denote the ratio of the actual density of the Universe to the critical density. 
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