Across all disciplines of science there exists an abundance of unanswered questions and mysteries that have endured for as long as humans have attempted to solve them.

Perhaps one of the most query-filled fields is physics, which continues to confound even the most brilliant minds. While it’s unlikely that all these quandaries will be answered in our lifetime, some of them may well could be.

In theory, the Big Bang should have created as much matter as antimatter in the universe. But it didn’t — at least not as far as physicists can see. Matter is everywhere, all around us — it makes up everything. But so far, we’ve only found small amounts of antimatter.

Why is that? Shouldn’t a particle of matter have an antimatter counterpart? It must be that the laws of the universe and nature just don’t apply to antimatter the same way they do to matter. Scientists have to figure out why that is and what it means for the universe.

For all we can see of our universe, there’s much more that we have yet to see — in part because it’s made up of invisible stuff called dark energy and dark matter. The thing is, we haven’t even actually visualized dark matter — only the effect it has on what we can see.

Physicists are trying to gain a deeper understanding of the invisible force by studying the behavior of stars and galaxies which appear to react to the presence of it. It is, however, a challenge to study something we can’t see. We need technology to catch up and let us come face-to-face with these “dark” substances.

One of the simplest questions to ask may be one of the hardest to answer:

Asking how big, or how old, the universe is depends on what part of the universe you’re talking about: the observable universe, or the entirety of it. We know through studying light that the observable universe is around 13.8 billion years old — that’s 46 billion light years. Determining how big even the observable universe is presents challenges because it isn’t a static entity: the universe is still expanding.

Even though we don’t quite have a handle on our own universe, it hasn’t stopped us from wondering if there are others out there — particularly so-called parallel universes. The idea is part of the multiverse theory, for which there are at least five accepted theories.

Those who don’t think it’s possible point out that after the Big Bang, with all that matter taking up space in space, inflation would have slowed down. Because it slowed down, if there were multiverses they wouldn’t beexpanding at the same rate as our universe is. That would throw a wrench in the idea of a truly parallel universe.

This is merely a fraction of the questions physicists are asking, and it all kind of comes down to answering one final question: what’s the ultimate fate of the universe? How will it end? Some theories posit that it will be a lot like how it began: a big bang. More specifically, a big crunch. One of the most prominent theories about the inevitable death of the universe is that eventually, as the universe expands, it will eventually reach a densitythat exceeds critical density — at which point it would collapse in on itself in an event referred to as the Big Crunch.

Of course, that’s just one theory. Another posits that the end will be more of an endless void — but in either case, it won’t happen for billions, if not trillions, of years. As far as we know, anyway.

References: Livescience, CERN, National Georgraphic, Phys.org