Great idea for a thread!!!
Big up UnOriginalNuttah!
I am not familliar with the multiple Big Bang theory, it must be quite new - I will therefore not express any opinions on it until I have researched the topic thoroughly. It seems to me to be quite a radical theory.
In answer to your initial supposition that time did not begin with the Big Bang, I would suggest that time and space are more closely linked than you seem to believe. Minkowski first introduced the concept of spacetime which is defined as a curved (or flat in special relativity), 4 dimensional, Lorentzian continuum that does not conform to the rules of Euclidian geometry. Without space, time cannot exist. Before the Big Bang (in the area inhabited by our universe at least, in the case of the theory of multiple Big Bangs - which would complicate things enormously and I cannot see how this theory can fit in with relativity) there was no space and therefore no time (at least that is what the most commonly accepted theories state - I don't come up with these ideas, I struggle to even understand some of them).
To discuss the Big Bang theory we must first take into account the evolution of successful physical theories throughout history. The most succesful of which have been those theories based on the concepts of dynamics. The specification of how a physical system(let us assume that the universe is a physical system) will develop with time, given the physical state of the system at one particular time.
The theories behind dynamics are many and varied. The most important ideas however are Newtonian dynamics, Keplers laws of geometric motions and above all the laws of thermodynamics (1. Conservation of energy within a system. 2. Heat flows from a hotter to colder body).
I will assume that everyone contributing to this thread knows, at least, the basics of these laws.
Since a lot of the ideas behind the creation and evolution of the universe deal with obtaining finite solutions to problems that have factors that may be infinite then a basic understanding of quantum mechanics will help, particularly schroedingers wave equation.
As modern theories go spacetime did indeed begin with the Big Bang. It is important to grasp the concept of all space being formed in this manner, not just all matter (theorists do disagree about this fact but the majority believe that if the universe is indeed finite, then beyond the universe there would be no space - nothing, not a vacuum, nothing.
Theoreticians often try to distinguish between open and closed systems. This is an important distintion when entropy is an issue, as it is with understanding the energies within the universe. A closed system cannot be affected by energies beyond it in any way, a closed system cannot therefore exist, except of course in the case of a finite universe that is being considered in it's entirety. Time-asymmetry in the 2nd law can be explained by these external influences. Even if the universe is infinite, as some believe, it can be considered as a whole for the sake of being a single system. We shall call the system (universe) U.
Treating the universe as a whole brings up issues that need to be explained through cosmology. Understanding the basics of general relativity (if you don't know much about general relativity read wiki (or even better a book about it), it is quite interesting) is important for this, for example gravitation should NOT be regarded as a force, but as spacetime curvature in accordance with Einsteins principle of general convariance. It is necessary for us to describe the universe with no specifcally chosen time coordinate with respect to which the universe is supposed to evolve. As I have stated earlier a dynamic model of a physical system, is based upon temporal evolution - therefore we can represent the universe as a point x
moving through phase-space P. Every location of x will stand for a spatial description of the system at a single point in time. A bigger picture of what is going on can be obtained by taking a more relativistic view of the system (universe), but it makes everything far more complicated. There is (I'm not going to bother explaining it so you'll have to take my word for it) a naturally defined time coordinate that can be obtained for the cosmological models in question, we shall call this time coordinate t. The whole universe can be considered to be evolving with respect to t. A phase-space Pu can describe the broad totality of possible universes, with all their evolutions dependent on classical dynamical equations. Each point of Pu describes the all matter within the universe U at time t as well as the distribution of continuous fields, such as gravity. This means that the universes spatial geometry and it's rate of change will be shown by the location of x within Pu.
As I have already stated in another thread Pu will be infinite-dimensional, regardless of whether of not U is infinite. This is also a feature of other fields such as electromagnetism. It becomes difficult to define entropy within a system such as this, since each phase-space region V will be of infinite volume. Using ideas from quantum (field) theory finite answers can be obtained from the phase-space volumes with reference to systems that are appropriately bounded in energy and spatial dimension. Unfortunately to date I am unaware of any theory of quantum gravity, but this does not matter too much in exploring the question of the 2nd law.
The entropy increase in the 2nd law is not just a necessary by product of the universes expansion, since the actual entropy of the universe would increase in line with it's expansion. The dynamics of general relativity are described equally well by the motion of point x within Pu as all other physical processes. Phase space simply exists and does not in any way grow with time as Pu is independent of time. Since all states within Pu are dynamically accessible to the universe (or universes) there can be no 'entropy ceilling'.
Right - that's enough thinking for one night, I'll write some more in the morning. Hopefully then I'll get onto the entropies involved in the Big Crunch using Bekenstein-Hawking entropy formula - after a bit about black holes and singularities - because they are very important in out understanding of energies in spacetime.
Bedtime...