Q1: Did the beginning start with a "Big Bang?
Not necessarily. The most popular cosmologies have the universe, sometimes one universe after another, going on forever. The latest, the cyclic universe is one unverse. A previous one, Smolin's black hole which I like, but he has disowned, has supermassive black holes producing baby universes in something like a series of big bangs. The original multi-universe based on choatic inflation by Andre Linde has numerous universes coming from the void of inflation. But nobody knows anything for sure.
Q2: What caused the beginning to happen?
The whole idea of a beginning is an assumption. That Tuft's guy whose name I cannot (Velenkin)spell had the best beginning by having it all come from a quantum fluctuation. But I do not like his cosmology. But again, nobody knows for sure. It's all speculation
Q3: If the so-called "Missing Mass" is found in our Universe, will this be sufficient to cause the "Big Crunch"?
This is a question with a known answer. We know how much missing matter there is and it is only 30% of the amount needed to cause a Big Crunch. By the way, there are no singularities in nature. That is just a math approximation. That is the basis of renormalization theory in quantum mechanics, that singularities cannot exist. It is one of the basic principles of all physics.
Q4: Will our known Universe continue to expand and eventually die, or will it expand and grow?
From what we now know, the universe will expand forever and all stars will eventually die out. But that is based on present conditions. For example, in the speculative (but based on good physics) cyclic universe, the universe eventually renews itself. BTW, the universe does not expand into nothingness. As far as we know the universe may be infinite and expanding.
Q6: What is "Nothingness"?
Who cares. It is not the crux of anything. Do not waste your time worrying about it. It does not exist, which is its best definition. Nothingness is what does not exist. Or nothingness does not exist.
Q7: Doesn't the background radiation, in the Universe, prove that there must have been a big bang?
No. It just proves that the universe we live in was very hot once upon a time.
Q8: How can something come from Nothing?
It does not. You are assuming that the speculative cosmology you have been thinking about is true. It ain't necessarily so. More likely that something came from something.
Q9: Is our Universe infinite and unbounded?
Nobody knows the answer to this including you. Your argument is incorrect. The universe could be infinite, but because it is expanding beyond the speed of light, we will never know.
Q10: How is our known Universe shaped?
Do not try to describe something that you nor anybody else knows anything about. Recognize that it is all speculation. Solutions to Einstein's equation all involve speculative assumptions. And the number of such solutions abound.
Q11: Do the laws of nature, we have discovered, apply everywhere?
Again nobody knows, including you, and most of us serious physicists do not care either. It is just good meat for a rap session.
Q12: Does the whole (Cosmos) have a finite size or is it infinite?
Nobody knows. It's all speculation. Logic does not apply here. You do not know that it all came from nothing. Get over it. Well, that's too strong. Do not stop being imaginative. But it's like smokin'. After you sober up you may find that all those great ideas were just that- great ideas, and nothing more. But the flight of imagination is very important for life and for doing physics. Just hang on to what you know for sure is true and look at the rest as possibilities. It takes much work in physics to make possibilities real. Even then, nothing is know for sure. ( A play on your words illustrating the limitations of the English language)
Q13: If there was absolutely Nothing in the beginning, where did God come from?
I like Smolin's black hole creation model best because it allows for a separate god for each baby universe. And I can even envision how the god came into existence from the preceeding universe, a collective form of all of us intelligences being created right now. It even is consistent with thye Hindu image that Vishnu is sitting on a coiled snake with new universes coming out of his nose (found in the Shri Bagavatum)
But again it all speculation. More than that it makes for mythology. Big Bang is essentially mythology, modern scientific mythology that is consistent with known principles of physics, but nevertheless all speculation.
Q14: Why did the beginning happen?
Personally I do not think there was a begginning, except maybe the Smolin type beginning. Nobody knows why. I like to think its all to create intelligence and consciousness. But that may be just narrow mindedness as i think I am intelligence and conscious.
Q15: How did the Nothingness create Something?
Do not even pretend that you know what you are talking about. It's all rhetoric. Nothingness does not exist.
Q16: If everything came from Nothing, how did Nothing make Energy and Matter?
Q17: Do the physical laws that we understand apply to our entire known Universe?
Astronomical observations suggest that that is true. However, it is also assumed to be true in the analysis. BTW, when you say the known universe, that restricts it to the part of the universe that we can see. Known physical laws may not apply to dark matter or dark energy.
Q18: Why is the Universe the way it is?
It just is or we would not be here to see it.
Q19: Can this concept of Nothingness really be the answer to the true beginning? No
Q20: Will our Universe eventually die?
Who knows. I do not care. It will last for at least 5 billion more years. We should last so long.
Q21: Will we ever understand everything about our Universe?
No . We do not even know what reality is. Take quantum mechanics for example. I know of 4 different interpretations that point to 4 different realities. Vastly different assumptions yield the same equations. Throw in GR and string theory and we are clueless as to what our universe really is.
Q22: Why is our science so convinced that the beginning started with a Big Bang?
That is a mistaken notion on your part. To be fair, it is how big science is promoting itself. All we know for sure is that the universe we can see is expanding and it once was hot. That's it. The rest is baloney. BTW, it could have all started from a piece of baloney. That cannot be disproven.
Q23: The argument for a singularity is very strong - why did the beginning not start with a singularity?
The argument from a singularity is very weak because singularities cannot exist in nature. The closest thing to a singularity is the GR solution for a black hole. But the singularity there is just a math approximation. The singularity really consists of a membrane across which matter is destroyed and a unified field is formed. (My speculation). It is out of this unified field that new universes are formed according to Smolin. Pictures of that process can be found in Greene's book "The Elegant Universe".
Here is where something may come from nothing as the amount of phase space swallowed up by the black hole is nowhere nearly enough to create a new universe. Somehow much more phase space in created inside the black hole membrane that we call a singularity.
But pahse space is a math concept that at most has to do with available information. Perhaps the real miracle of universes is that they create more space to hold information.
Q24: Why is imagination more important than knowledge in determining the true nature of the beginning?
Nobody knows what is really true about anything if we look closely enough. Imagination is great for creating myth. And myth is important for happiness. It's the basis of religion. And it could even be true. But we will never know for sure. We know nothing for sure. It's all probabilities. I'm 99% sure I exist, but only 80% sure you exist. And it's 50-50 that something like a big bang ever happened.
Q25: Can empirical science lead us eventually to the truth about the beginning?
False premise. Most likely there was no beginning.
Q26: Are we creating our own Universal reality?
We are creating myth. I assume the universe exists without us, as that was true for seemimgly 10 billion years before we existed. But some people think we are now creating the universe.
Q27: The boundary between something and nothing, what's it like?
No such thing. You are just foolin' yourself if you think you know.
Q28: Is it correct to say that the "Concept of Nothingness", as a proposal for the beginning, can never be challenged? FALSE......
Everything I have said in this post challenges it.
Q29: Empirical science has to be the correct approach to understanding our Universe - therefore if science is suggesting a big bang as the beginning, how can Nothingness ever be considered as a viable model?
Not true. We have never seen the beginning. There is no empirical support for a beginning. All we see is expansion and some microwaves that theoretically suggest that the universe was once hot. That's it. Get all that other myth out of your head if you think for one minute that any of it is true.
Q30: Does there have to be a conflict between current models of the very beginning and the concept of Nothingness?
My god there is a conflict in what quantum mechanics is based on. No need to invoke myth to find conflict.
Q31: Even with pure Nothingness, surely some purpose or design had to be in place to initiate the beginning?
There seems to be symmetries in nature from which all the know laws of physics can be derived. Did someone have to design the symmetries. I have heard it argued that the symmetries have to exist for us to exist. No need for a designer. Just a need for us. But I never put much stick in that argument.
Q32: If we can never comprehend Nothingness, what is the point of debating this abstract subject?
It gets the imagination going and that's the most important tool at man's disposal, so let's use it.....
Nothingness does not exist, period. Imagination does exist. Use it. But do not necessarily believe in it.
Q33: How can imagination, within the confines of this known Universe, help us to grasp some understanding of Nothingness?
No need to understand what does not exist.
Sorry if I stepped on some of your imaginative toes, but I have given you a typical, i believe, physicists response to your questions, and your answers. Religion is OK and myth is OK if you remember that none of it has to be true. You know the old adage "My GOD is batter than your GOD" It applies to scientists as well except you have to substitute the word theory for god. It produces the same brand of narrow mindedness.