Big bang theory really a term describing the moment the universe started and not the evolution and how things evolved with time which have more questions than answer. The standard model of cosmology is the most accepted theory about universe. But you can't have knowledge about anything before the singularity. Actually we don't even know for sure what happens in the seconds after that because we need a much more powerful colliders than what we have now to produce the same conditions. But there are many theories about what could have happened.

Consider the bbt as a collection of observations and models that are independently validated. As each of those components reach increasingly accurate representations of what we observe, the bbt improves.

In this way, there can be no alternative as there is no alternative to music theory. Some people may have a very narrow view of music theory, but it truly encompasses every model we accept about aspects of music.

Tldr- the questions can't be answered because the bbt is a not a theory like "THE theory of relativity". The "theory" is at the end of the term which denotes a collection and not a specific model.

Big Bang Theory is a bunch of really solid observations and hypotheses mixed with a bunch of open questions, even about the fundamental nature of forces.

It was only 30 years ago that we discovered what we call now dark energy. And it turns out that within that short time frame we have multiple ways of measuring the amount of it, and those methods agree. There is more dark energy than dark matter, and that the visible matter is even a small fraction of the dark matter. But even with this discovery of the acceleration of expansion of the universe, the core big bang theory holds.

There are many alternatives to the predominant and not-yet-accepted-as-true Lambda-Cold Dark Matter model of physics, such as Timescapes, but none of them have enough evidence behind them to be considered serious alternatives at the moment.

Things like the Baryonic Acoustic Oscillation theoretical predictions, that are visualized in the spacing of galaxies, are literally mind blowing to me. Theoretical physics predicted how matter would behave when it's so hot and dense that none of it can even form atoms, and it predicts the structure of all sorts of things, even the variability we observe in the cosmic microwave background.

TL;DR The depth and consistency of observation that point to a big bang are stunning. But we still have so much we don't know about the particulars, and the fundamental forces.

> Off topic: > > - Is the big bang theory the scientific consensus on the origin and evolution of the universe ?

Yes, because this theory currently best describes our observations, but there are still many anomalies. Like dark matter / energy / quantum physics / axis of evil.

> - What are the alternatives ?

The big crunch, where the universe ultimately shrinks again. You also have a theory that it expands and shrinks and loops like that. You also have several string theories where they propose that the whole universe is a hologram projection of a higher dimension.

But these theories are lacking certain important explanations of certain observations we have, that most people still keep the Big Bang Theory as the most accurate.

The first four explanations of illustrations in my book delve into your off-topic point and bring it back on-topic:

https://impacts.to/downloads/lowres/impacts.pdf

Big Flash.

https://www.youtube.com/watch?v=eSSDi22NVFo

As if matter existed and then there was a creation of light at some moment. Red shift is explained by interaction of light with gravitational field - the more distant source of light, the longer it travels under the influence of gravity and the more red it becomes.