Originally Posted by Antarctica!

Risu unearthed his impressed face again. "Have you been sneakily reading up on relativity, Mr Miner?" he asked, looking at the boy shrewdly. "Twins on a spacecraft feature in one of the most famous thought experiments of relativity, and we will get to that experiment in a moment. But first..."

He hoped the rest of the class was still listening. "Regarding your example. You're correct. Blaine on the, er, train would age slower than his twin - let's call her Patricia - would just sitting around. Now, in reality, the age difference would be absolutely tiny, as trains aren't moving very fast at all. On a, you know, relativistic scale. Even travelling for 30 years would only lead to an age difference of a fraction of a second. For time to slow down noticeably, Blaine's train needs to be moving at an appreciable fraction of the speed of light. For example, if you somehow managed to get the train moving at around 90 percent the speed of light, time would only tick half as fast for Blaine. In that case, getting off the train at 30, his twin Patricia would be 60 years old already."

He looked at Alex questioningly. "Clear so far?"