Einstein's Twin Paradox is super confusing for me, every time I think I fully understand it, I find more questions. The Twin Paradox is a thought experiment in special relativity when one twin travels to outer space while the other twin stays on Earth. When the space bound twin lands back on Earth, he'll find that his Earthbound twin has aged much more than he has. Why is that? Watch this video to find out the simple explanation with animated cartoons. [Kuriositas via Neatorama]
NASA should not train astronauts that have twin brothers because that eventually could destroy the world or something like that, the universe just don't like paradoxes.
Also, that "paradox" have real world effects. The GPS system must have to take it into account to work.