I would vote for "How did some cosmic rays get so much energy?" At least we know for sure they exist. Dark matter may not. - It is just the best explaination of some data that is only a few years old (less than 20% as long as the CR mystery has been around without any plausibe solution) Black holes in the sense of very stong gravity, so strong that light can not escape, very likely do exist, but not necessarily any points with infinite density.
For me it's the presence and nature of other intelligent life. The other questions are fascinating but I'm not sure I'd appreciate the 'answers' even if presented in simplistic terms. Quantum mechanics is 'wierd' and answers a lot of questions but does little for my own understanding. I can understand the 'science' of QM but the perception of reality via my physical senses is limited (as it is for all humans).l
This is a problem in semantics, not cosmology. This is like asking, "What are the properties of an object when its temperature drops below absolute zero?" Both questions are syntactically correct in our language and therefore the words can be uttered or written, but they are meaningless in the context of science. The universe does not have an "edge" because that implies a boundary between what is inside the universe and what is outside. The universe instead has a limit, like temperature, which implies that there is no such thing as "beyond the limit." To say, "There is nothing outside the universe," is an ambiguous statement because it makes it sound like the universe has an outside and there doesn't happen to be anything there. What we mean to say is, "There is no outside to the universe. The universe is all there is." If you graph space on an inverse-log scale, the limit of the universe is at infinity. Considering that it is impossible for us to travel to the limit of the universe because it is expanding at the speed of light (or perhaps faster, Walter Wagner keeps trying to explain this to me), from our perspective what your husband calls the "edge" of the universe truly is at infinity. I have long recommended graphing time on a log scale for a similar reason. This will put the Big Bang at minus infinity, obviating the question, "What came before the Big Bang?" This would give time an absolute zero like temperature.
LOL, I have no idea what you just said, but I'll let my husband read it. Thanks Fraggle! I don't suppose anyone could explain to me what an Event Horizon is? (in elementary school terms please)