Though we have made leaps and bounds in the acquiring of scientific knowledge and understanding, there are still some questions that science cannot answer. At least, not definitively. Here are a few. They may boggle your mind, make you roll your eyes, or make you confused. Either way, they're amusing and interesting.

Do you know the answer?

1. Is the universe infinite? If it is, doesn't that mean it can't expand?

I've heard two simultaneous statements, which can't exactly coexist and both be true. Either the universe is infinite, and goes on forever, or it is finite, and expands. Which one is it? And if the universe is expanding, what is it expanding into? Nothingness? Is that nothingness infinite?

2. How could time travel exist?

Let's discuss a hypothetical situation. A man travels back in time to kill his father. Suppose he succeeds, and his father dies. This means that the man would never have been born to kill his father in the first place, creating a paradox. If anything in the past is changed, then the future changes, the very future you came back from, meaning you couldn't have come back in the first place (as your future no longer exists). Doesn't this (an example of the Grandfather Paradox), mean time travel cannot exist?

3. What existed before the Big Bang?

Was there anything? Was everything simply nothingness? The Big Bang Theory states that during the first seconds of the universe, fundamental particles such as electrons existed, which either combined with others or decayed over time. Then, what existed before the first second of the universe? Didn't something have to exist, if fundamental particles existed? Doesn't that mean there technically is no first second of the universe, that it is infinite?

We can speculate, calculate, and experiment, but can never truly know the answer to such far-reaching questions.

I suppose, in a way, that the uncertainty makes them all the more enticing and compelling.