We know that Einstein's theory of special relativity established that speed could change time. But that was all the way in the twentieth century! Speed had already changed time about fifty years earlier, all across America, because of one special invention.

There was an era in history, American history, during which every locality had its own time. People who didn't have access to satellite systems or even, necessarily, telegraphs, waited until the sun was directly overhead and set their clocks to noon. No one cared if their town clock was a few minutes off. And no one cared if the next town over had their noon at a slightly different time.


Even if someone galloped over on a horse, the time difference was minimal. If people made longer trips, they were more concerned with getting there alive (as anyone who has played Oregon Trail knows) than worrying about the difference in local time. After several weeks of walking barefoot across the plains hoping your oxen doesn't throw a shoe and strand you all in a wintery path where you will eat each other, it doesn't matter if noon is suddenly later when you get to Kansas. Odds were, there was nothing in Kansas (or almost any other state) that you needed to be exactly on time for anyway.

Then came the railroad. The railroad was fast, and suddenly what had been the journey of months became a journey of weeks or even days. The railroad also had to be kept fast – and profitable – and that meant selling tickets up and down the line, and telling people when they had to be at the station to get on board. In a country where every ten miles had its own time, where each time was reset whenever people noticed that the season had changed enough that the sun wasn't overhead at noon, and where some people measured the time inaccurately, this was damn near impossible. And so, in 1883, there was something called the General Time Convention (which needs to be an episode of Doctor Who). There the heads of American railroads set out five time zones across the continent. When we acquired speed, we acquired the necessity to change time.

[Sources : Mad Science]