who is the observer?

Question

If I am sitting on a rock in space and an alien on an asteroid passes me by super fast, does the alien age slower than me? I am confused because from the alien’s point of view I am moving super fast. So who ages slower like in Ender’s Game?

In: 8

Answer 1

> So who ages slower like in Ender’s Game?

Both of you!

This is a weird, counter-intuitive aspect of Special Relativity.

As you note, from your perspective you are stationary and the alien is moving, so the alien’s clock runs slower than yours (a minute for you could be only 40 seconds for them).

But from their perspective, *they* are stationary and you are moving, so your clock runs slower than theirs.

And each of your frames of reference is perfectly valid!

Which is (kind of) the point of the Twin Paradox; we have an apparent paradox, both your clocks should run slower than the other’s.

Oddly enough this actually works out fine as *there is no way for you to compare clocks again* without one of you accelerating (i.e. one of you slowing down to stop with the other), and accelerating is what skews up relative time and space. If a third party gets involved (say someone passes them going the other way and then meets up with you) the maths works out fine from their perspective as well, and they get a result that is consistent with what both you and the alien experience.

The maths of Special Relativity is deceptively simple (largely equations of straight lines), but produces some wonderfully weird results.

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As an afterthought, because you specifically mentioned Ender’s Game; Ender’s Game contradicts Special Relativity as it hinges on faster-than-light communication. So in the Ender’s Game world this situation doesn’t work and you get the paradoxical situation; when the Earth military contacts the distant fleets less time should have passed for the fleets than back on Earth from the Earth’s perspective, but less time should have passed on Earth than on the fleets from their perspective [disclaimer; I haven’t run the numbers to confirm this, but I think it works this way] – the situation is logically impossible.