I would add that this article here is an important philosophical one to compliment the above:
http://www.bethinking.org/is-there-a-cr ... e-big-bang
This part here is interesting, especially for those that believe in the "big crunch":
Oscillating Models
The Standard Model was based on the assumptions of homogeneity and isotropy. In the 1960s and '70s some cosmologists suggested that by denying homogeneity and isotropy, one might be able to craft an Oscillating Model of the universe and thus avert the absolute beginning predicted by the Standard Model (Lifschitz and Khalatnikov 1963: 207). If the internal gravitational pull of the mass of the universe were able to overcome the force of its expansion, then the expansion could be reversed into a cosmic contraction, a Big Crunch. If the universe were not homogeneous and isotropic, then the collapsing universe might not coalesce at a point, but the material contents of the universe might pass by one another, so that the universe would appear to bounce back from the contraction into a new expansion phase. If this process could be repeated indefinitely, then an absolute beginning of the universe might be avoided (Fig. 3).
Such a theory is extraordinarily speculative, but again there were metaphysical motivations for adopting this model.[5] The prospects of the Oscillating Model were severely dimmed in 1970, however, by Roger Penrose and Stephen Hawking’s formulation of the Singularity Theorems which bear their names (Penrose 1965: 57-9; Hawking and Penrose 1973: 266). The theorems disclosed that under very generalized conditions an initial cosmological singularity is inevitable, even for inhomogeneous and non-isotropic universes. Reflecting on the impact of this discovery, Hawking notes that the Hawking-Penrose Singularity Theorems ‘led to the abandonment of attempts (mainly by the Russians) to argue that there was a previous contracting phase and a non-singular bounce into expansion. Instead almost everyone now believes that the universe, and time itself, had a beginning at the big bang’ (Hawking and Penrose 1996: 20).
Despite the fact that no space-time trajectory can be extended through a singularity, the Oscillating Model exhibited a stubborn persistence. Three further strikes were lodged against it. First, there are no known physics which would cause a collapsing universe to bounce back to a new expansion. If, in defiance of the Hawking-Penrose Singularity Theorems, the universe rebounds, this is predicated upon a physics which is completely unknown. Physics predicts that a universe in a state of gravitational self-collapse will not rebound like a basketball dropped to the floor, but rather land like a lump of clay (Guth and Sher 1983: 505-06; Bludman 1984: 319-22). Second, the observational evidence indicates that the mean mass density of the universe is insufficient to generate enough gravitational attraction to halt and reverse the expansion. Tests employing a variety of techniques for measuring the density of the universe and the deceleration of the expansion continue to point to a density below the critical value. In January of 1998 astronomical teams from Princeton, Yale, the Lawrence Berkeley National Laboratory, and the Harvard-Smithsonian Astrophysics Institute reported at the American Astronomical Society meeting that their various tests all show that ‘the universe will expand forever’.[6] A spokesman for the Harvard-Smithsonian team stated that they were now at least 95% certain that ‘the density of matter is insufficient to halt the expansion of the universe’.[7] This effectively rules out an oscillating universe. Third, the thermodynamic properties of an Oscillating Model imply the very beginning its proponents sought to avoid. Entropy increases from cycle to cycle in such a model, which has the effect of generating larger and longer oscillations with each successive cycle (Fig. 4).
Thus, as one traces the oscillations back in time, they become progressively smaller until one reaches a first and smallest oscillation. Zeldovich and Novikov conclude, ‘The multicycle model has an infinite future, but only a finite past’ (Novikov and Zeldovich 1973: 401-2). In fact, astronomer Joseph Silk estimates on the basis of current entropy levels that the universe cannot have gone through more than 100 previous oscillations (Silk 1989: 311-12). Even if this difficulty were avoided (Hochberg, Molina-Paris and Visser 1999), a universe oscillating from eternity past would require an infinitely precise tuning of initial conditions in order to perdure through an infinite number of successive bounces. A universe rebounding from a single, infinitely long contraction is, if entropy increases during the contracting phase, thermodynamically untenable and incompatible with the initial low entropy condition of our expanding phase; postulating an entropy decrease during the contracting phase in order to escape this problem would require us to postulate inexplicably special low entropy conditions at the time of the bounce in the life of an infinitely evolving universe. Such a low entropy condition at the beginning of the expansion is more plausibly accounted for by the presence of a singularity or some sort of quantum creation event.
Although these difficulties were well-known, proponents of the Oscillating Model tenaciously clung to it until a new alternative to the Standard Model emerged during the 1970s.[8] Looking back, quantum cosmologist Christopher Isham muses:
“Perhaps the best argument in favor of the thesis that the Big Bang supports theism is the obvious unease with which it is greeted by some atheist physicists. At times this has led to scientific ideas, such as continuous creation or an oscillating universe, being advanced with a tenacity which so exceeds their intrinsic worth that one can only suspect the operation of psychological forces lying very much deeper than the usual academic desire of a theorist to support his/her theory” (Isham 1988: 378).
The Oscillating Model drew its life from its avoidance of an absolute beginning of the universe; but once other models became available claiming to offer the same benefit, the Oscillating Model sank into oblivion under the weight of its own deficiencies.