What are the rules to describe those changes?
One important consideration is that the rules to describe those changes should be independent of any human involvement.
One of the most physical parameters which we use is visible light. In order to observe the physical reality we use visible light, however the concept of visible light can not be used in any law, because visible light is a human related parameter. Instead what we should use is electro magnetic radiation. In order to specify more in detail what we want is to use frequency (or wave length).
A typical parameter which depents on visibility is the concept of dark matter. You can not divide matter (mass) in visible versus invisible. You should only use baryonic and non baryonic if that is sufficient.
One parameters which IMO should also not be used to describe the rules of the Universe is absolute.
The problem that you can not use the word absolute because how you define what is absolute. In fact the whole Universe is in a certain way absolute. But if that is true the concept absolute has no meaning.
A parameter which can be used is relatif, however with care. For example you can write that the relative speed between two trains is 100km/sec.
IMO the most important issue is to define a reference frame. The reference frame is at rest and you can also call it absolute. The rules of physics should be described based on this reference frame.
Fishes in a Pond
In order to describe the evolution of galaxy formation the following scenario should be studied.
The title of this paragraph is Fishes in a Pond. This sounds strange. Read the paragraph to its end and it becomes clear
In my garden I have a pond. In the pond there are fishes. First you buy large ones but sooner or later you get also small ones.
Now feeding becomes a problem. In order to feed them, I have special fish feed. This feed comes in pellets, in large ones and small ones.
Normally I have both sizes. However the small ones where out of stock. What to do. I toke the larger ones and used a hammer to make very small ones, almost like dust particles. Those "dust" particles I sprengled above the water. What happens when you do that they spread out like a film over the whole water surface. Next something happens, and that is the interesting part, some of those dust particles start to move towards each other until they touched each others. Next other particles joined. In short intially you have 100 individual particles and after 10 minutes you have 20 collections of roughly 5 particles each. The longer you wait the less collections you get but the larger each collection becomes.
How do you explain this behavior?
Fishes in a Pond  part 2
The previous paragraph ends with the sentence: How do you explain this behavior?
However a much more important phylosophical question is: Is there really an explanation for this behaviour.
A more or less similar phenomena is what is called the Casimir effect
You can try to find the explanation of the effect by studing what is called surface tension.
When you have 1 particle the surface tension from all sides is identical, keeping the particle in equilibrium.
When you have two particles far away each particle is in equilibrium. However when you bring the particles closer to gether this equilibrium is broken and the resulting force will move the particles, until they touch each other.
The important question is: is this a true explanation? IMO the answer is no. What you do is: you break the problem down in smaller elements (one of which is surface tension) which elements you can study separately but, and that is the important thing, there exist no complete explanation. The feature that small particles congregate in heaps is just a feature of nature. Even if you add some energy sauce to this description is does not explain every thing in detail.
What are the rules to describe what happened after the Big Bang
It is not the intention here to discuss all processes but only the ones related to the Big Bang.
In order to describe the Big Bang we use Friedmann's equation.
For detail goto:
Friedmann's equation  13 questions
Friedmann's equation the radius R(t) depents on 4 cosmological constants: Lambda, C (mass), k and "the age of the Universe" and it is the chalenge of science to calculate those constants by means of observations as accurate as possible.
However there is also a different version. In this case the Hubble function H(t) depends on the cosmological parameters: H0, Omega(Lambda), Omega(m) and Omega(k). There is one problem: all the parameters are a function of t.
For the current state of the art (as of 21 March 2013) of those parameters read this:
Planck Mission Brings Universe Into Sharp Focus
For technical papers read this: Planck 2013 result papers
What is involved to discover those rules related to the Big Bang?
This paragraph describes what is involved to discover the rules that describe the evolution of the Universe after the Big Bang. 6 Steps can be considered:

The first strategy is to calculate all the parameters of the Friedmann equation by one type of experiment. One example is to use SuperNova 1A data. The problem is the conversion from Luminosity to magtitude. This relation is m = L/d^2. With d being the light travel distance. The problem is that this equation does not work. The measured magtitude is smaller than expected. To solve that you have to modify this relation.
Document (1) Seven Year WMAP, Cosmological Interpretation at page 14 the two light curve fitting programs SALT II and MLCS2K2 are discussed. The problem is that the results of both programs are different which leads to the conclusion that SN data is almost not used.

A second strategy is to use the CMB radiation data. This strategy requires a Power Spectrum. Exactly how this Power Spectrum is calculated based on observations (CMB radiation data) is not clear. See Map reveals strange cosmos for details. The Power Spectrum as a function of the parameters Omega(Lambda), Omega(m) and Omega(k) is done by using the program CAMB. The astronomical community is lucky that there is only one version of CAMB because otherwise the same situation could arise as in the case of SN 1A situation.

The use of the program CAMB however leads to more questions.
 First what is the proof that the program CAMB is correct? IMO there exists not such a prove. That does not mean that the program is wrong.
 Input to the program is the Hubble constant H0. H0 is the Hubble parameter at t=0. H0 is calculated by assuming the lineair relation v = c * z = H * d. The result is the relation H = H0 = c * z / d . The problem is that the result of this calculation cannot be used because the correct relation H(z) is nonlineair. Specific H0 can only be calculated for very small z resp d values. For more information visit: Hubble's Law  6 Questions
 If you want to understand the laws of nature, what you have to do are three things:
 First you have to perform as many observations as possible over a long range of time for all the different parameters involved. Examples are positions, times, counts, frequencies etc.
 Secondly you have to establish the mathematical relations between those parameters. Those relations include constants which are unknown.
 Third you have to write a program which includes all the equations, which uses as input all the measurements and the output are the constants you want. To do that you need some form of least error fitting or some type of Monte Carlo approach.
The point I want to make is that in general you cannot divide the equations in two parts and first calculate a subset of those constants and secondly use this subset to calculate the others. You can only do that if those two sets are 100% indepent of each other or if you recalculate all the constants in the final calculation.
In the program CAMB this is not done.
 Document (1) at page 16 equation 27 and 28 shows the extended friedmann equation used (I expect) in the program CAMB. This equation uses instead of Omega(m) the two parameters omage(Baryon) and omega(CDM). At least one more equation is required to define both parameters. The simplest equation is that omega(Baryon) / Omega(CDM) is a constant. The problem is you need proof that this is correct starting from the Big Bang to the present.
 The photons we are observe now are originating from a sphere at the outer layer of the Universe. They are no prove that the Universe at that moment was isotropic and homogeneous. It is easy possible that the density of photons and baryons was not the same in all directions and resembles something like a supernovae.
 Document (1) at page 14 in paragraph 3.2.5 "Time delay Distance" uses gravitational lenses to calculate the cosmological parameters. IMO you can do that if you consider this as an independent project with a more or less unique solution. What you should not do is to mix the results of two experiments which each other. For example you should not mix the results of SN 1A data with the results of experiments which involve gravitational lenses.
Created: 23 Januari 2013
Updated: 22 March 2013
For more about the CMB radiation read this: Friedmann's equation  Question 13
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