**Question:** If a train travelling faster than the speed of light goes around the world non-stop for a week. When the people get off the train would the people be in the future or just see the past?

Keywords: speedoflight, travel

@cavemancraig: that makes my head hurt. Physics ain’t my strong suit, but it seems as though it might be yours! Hopefully @Kyler can help you out with this one! ðŸ™‚

0That has to be what Albert Einstein called a “though experiment” because as far as we know nothing that has mass can start from still and accelerate to going faster than light.

Taking the question literally, they would be exactly one week in the future (from our point of view). If we allow the train to go just less than the speed of light (which is possible, even though we can’t actually do it yet) I think the theory of relativity suggests that time would have moved faster for them – that is, their watches would tell them they had been traveling for less than a week.

0Wow, amazing question. If we get over the fact that no normal object can travel that fast (weight increases as you approach the speed of light so the energey needed would be enormous) then I imagine you would come out essentially in the future, because time would go slower for those on the train compared to those on Earth. So people would have aged and things would have changed on Earth but you’d still be the same as when you left.

0I imagine they’d be pretty dizzy to start with.

According to my understanding of this type of thought experiment, they would get off the train they would see the current. They would be a week younger than those not on the train and their watches would prove this.

But an important question that needs asking is that as we’re talking about relativity you need to find out whos week are you taking about? A week on the train or a week on the ground? As far as I can figure, they’d be different.

0The answers already given are pretty good. Anything that moves close to the speed of light experiences what physicists call “time dilation”, which means they experience time differently. So no train can actually do that, but if it could, the people on the train would be a different age from what they would have been if they had just watched the train for a week!

We can actually see this effect in the satellites we use for GPS tracking. They are far above the earth and moving very fast, but we know exactly how different their clocks are, so with some fairly straightforward math we can correct for their different “ages”.

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