What are Dyson spheres? What would be involved in building one? How much energy would it cost, and could we ever pay it back?
What’s the temperature of deep space? Can it get any colder than that? How do we even define temperature when there’s nothing around?
How do we know that the universe doesn’t rotate? Why would it matter if it did? What does all this have to do with time travel?
What are blue straggler stars? How were they first discovered? What do they tell us about star clusters and the evolution of stars?
Is it possible for anything to travel faster than light? What about tachyons? How would faster-than-light travel break causality? And just what the heck is causality, anyway?