I'm thinking of entering the Breakthrough Junior Challenge. It is a global science video contest in which participants have to explain a hard science/math topic in a 3 min video. Right now I'm debating on these topics on space exploration/astrophysics:
spacecraft propulsion (how it works with chemical fuels, or how it will theoretically work with antimatter or nuclear fuel)
gravitational time dilation (as an effect of relativity and how it works)
why the universe is expanding (explanation of dark energy, a possible cause)
solar wind (what it is, its effects - i.e. northern lights)
So, these are the topics I have in mind right now. I personally have no preference but I want a topic that won't take me forever to research on and that I can explain in 3 minutes, yet be sufficiently complex. Can someone please help me? Thanks.