The Impossibility of Perpetual Motion Machines
Distances in the universe are really and truly mind-boggling. Even within our Solar System it takes light several hours to reach the outer planets. And it takes years and years to travel enormous distances between stars. The state-of-the-art spacecraft today would take tens of thousands of years to get to the star nearest to our system. It may appear that exploring new worlds in those parts will forever be confined to the realm of fantasy. But is it how it is to remain?