this is impossible for most people to comprehend. Modern science says that the universe has always existed and always will exist.
You can argue a cycle of implosions and inflations took place but what happen before the first cycle?
The bang of bangs? but what caused this?
We have a limit of about 14 billion years of our visbility in our universe. Lets just say our universe is the first one. What happened before that?
Also, is there any time in the "deepest" center of a black hole?
Modern science says that the universe has always existed and always will exist.
Science says no such thing. Modern science doesn't KNOW the answer to that particular question, though it is looking. The prevalent line of thinking right now is that the universe did have a beginning and that there technically was no "before" the universe, because time also began at the Big Bang. Since "before" is a concept of time, there could have been no such thing as "before" when time did not exist.
I've read this position elsewhere. To my best knowledge I have to agree with Galen. It is possible that the Universe always existed, it might not be so, but we can't tell because the theory that could inform us (General Relativity) breaks down in a (projected) singularity (at present still a synonym of surrender) also the case inside a black hole. And we don't have yet a theory that could inform us about what happens to spacetime whether it be loop quantum gravity, string theory or one of the other theories of quantum gravity or whether the singularity appears in space or space inside the singularity.
There seems to be an inversion of the role of space and time at the event horizon of a black hole. As seen from the outside time slows down to complete stop at the event horizon (redshift becomes infinite) while the black hole in it's entirety has a temperature, radiates away in surrounding space under conservation of information.
To me saying that there is nothing before big bang is like saying that in the origin of a river water materialises from nothing, and we know this is not true.
And to cosmologists, saying that there is nothing before the Big Bang is like saying that there is nothing South of the South pole, which makes more sense. To each their own.