Ok, got it.
I know, you have explained your background before. Btw, I am impressed with what you have achieved.
You don't need math to understand that math can't explain how the universe began. That is where I am coming from, I am not promoting any cosmological model, I am asking about the bb model. I am not yet convinced that it is correct. I don't doubt the math that does exist to explain the model sans very beginning is quite good as far as math goes, but models of reality are not equal to the reality, they are just a sort of thumb sketch relatively.
There are two problems that come with the models we find in science.
1. It is easy to take them too seriously. It should always be remembered that our models are our current best guess and may be changed when new information comes in.
2. It is also easy to not take them seriously enough. Since scientific models usually have been extensively tested, they have already shown themselves reliable in a wide variety of situations. Unless there is good observational reason to think they will fail, it is usually a good bet they will not.
When it comes to the Big Bang model, there are aspects that have been thoroughly tested and others that have not been.
For example, the basic model of an expanding universe whose expansion follows the parameters set out in General Relativity has been tested very extensively. We know that this model works well once we get into the stage of nucleosynthesis. The current consensus model based on a cosmological constant (also known as dark energy) and cold dark matter fits the observations incredibly well.
Are there things we don't understand? Yes, of course. We don't know the specifics of how the early galaxies and stars formed, for example. That isn't directly an aspect of the BB scenario, but an extension into galactogenesis. The BB model gives the background parameters, but there is a lot we don't know concerning the sequence and timing of many events.
So, expansion from a hot, dense universe with nuclear reactions, through a time of decoupling of matter from light, to an accelerated expansion is a solid sequence. Exactly when the first stars formed, when the first galaxies formed, how they formed, etc, is a collection of things we know significantly less about.
Prior to the stage of nucleosynthesis, things start becoming less certain. that is partly because we don't fully understand the particle physics for the energies (temperatures) involved, including the role of the HIgg's boson. So, while it is very likely that there was an early period of inflation (exponential expansion), this has not yet been verified and is closely related to some aspects of particle physics we are still learning about.
Prior to the inflationary stage, we have very little data to go on, which makes almost anything said speculation. But, what we know is that at some point quantum aspects of gravity become relevant. The basic BB model does NOT include quantum gravity (although energies less than those from quantum gravity can be handled). And we simply do not have anything close to a tested theory of quantum gravity. We have a LOT of speculation, but almost no hard data.
So, when it comes to some basic questions, like why the universe is mostly matter and has so little anti-matter, we simply don't know. When it comes to the question of why the energy density of a vacuum is what it is, we have almost nothing. Whether the 'singularity' that happens in the basic BB model is even still present in a full treatment involving quantum gravity is not known at all.
So, some questions, like whether there is a multiverse, whether time had a beginning, whether there is a 'cause' for the current expansion phase, and *many* others, simply don't have answers at this point. And, without hard data, we may never know the answers.
Having mathematical models keeps us honest to some extent. it prevents the type of hand waving that people tend to engage in when math is not involved. There is *still* some hand waving, of course, but the amount of it is cut down considerably.
But the precision of a mathematical model, especially when it works, can lead people to think it *must* be true. But all too often we have had good mathematical models that simply turn out to be wrong when extended to the next level. So, what will happen in quantum gravity is anyone's guess. How that will affect the question of whether the current expansion has a cause is also anyone's guess.
But that doesn't mean the basic BB model is wrong. It is incredibly good *in its domain*. But that domain does not include quantum gravity or the specifics of galaxy formation.
