The world around us is a pretty complicated place. And it's often overwhelming for scientists who want to understand more about the forces that control our Universe to know where to start. But as one our favourite astronomers, Alan Duffy from Swinburne University of Technology in Australia, explains in this TEDxYouth@Sydney talk, sometimes the most crucial discoveries come from asking some pretty obvious questions.

For example, Duffy explains that a few years ago, he was giving a talk at a school in a tiny town in Western Australia, when a girl put up her hand and asked why the Universe is so cold, when the Sun is so hot? It sounds like an overly simple question, right? Especially when Duffy is usually fielding queries from budding astronomers about the fastest objects in the Universe and the biggest galaxies and planets.

But it turns out that this is exactly the same question that German astronomer Heinrich Olbers asked back in the 18th century, known as Olbers' Paradox. And it triggered research that proved the Universe as we know it must have had a beginning. Because, just like the student at Duffy's talk suggested, if the Universe was infinite and stars have been burning forever, then space would actually be hot.

It's pretty crazy to think that our understanding of the origin of the Universe was triggered by a question about the temperature of space, but that's just the way science works sometimes.

In fact, Einstein's general theory of relativity also came from asking a very simple question, about whether we can tell the difference between the gravity that's keeping us stuck to the planet here on Earth, and the force that pushes astronauts back in their seats when they blast off in a rocket. 

The answer? There is no difference. And that insight led Einstein to discover that time passes more slowly for someone on Earth than it does for someone in orbit. 

And there's one more simple question that Duffy is now trying to answer at Swinburne, along with researchers around the world: What if the world was filled with invisible stuff? Not just invisible to us, but fundamentally invisible so it doesn't shine or absorb light, but still has mass?

We'll let you watch Duffy explain the answer to that in the video above, because he does such an awesome job of it. But allow yourself to be mind-blown by this for a second: that one question has led scientists to understand that galaxies are actually held together by ghosts.

So next time you're scared to ask a question because it's too stupid or seems really obvious, just remember that the simplest questions are sometimes the hardest to answer, and they've lead to some of the most important discoveries of our time.

Find out more about the innovative research happening at Swinburne University of Technology.