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  • One of the most revolutionary things we learned in the 20th century was that time is not absolute

  • – the rate at which time passes for you (or anything else in the universe) is different

  • depending on how fast you're moving and how much you're accelerating.

  • In particular: time passes slower the more you're moving.

  • This fact has been confirmed experimentally countless times – fast-moving muons take

  • longer to decay, light emitted from a moving source has a lower frequency , and so on.

  • But relativity of time can at first glance seem somewhat contradictory.

  • Suppose we're flying past each other; from my perspective it seems like you're moving

  • (and so time should go more slowly for you), and from your perspective it seems like I'm

  • moving (and so time should go more slowly for me).

  • It seems crazy that we can both think time is going slower for the other personsomeone's

  • time must actually be slower, right?

  • Well, no - take a look at my giraffe.

  • It's 3 meters tall.

  • And your giraffe is 3 meters tall, according to you.

  • But you're rotated relative to me, so you only measure my giraffe to be 2 meters high.

  • And I'm rotated relative to you, so I only measure your giraffe to be 2 meters high.

  • So we each think the other is measuring distances in space as longer, but it's not a contradiction.

  • It's just that we've rotated height and width relative to each other.

  • And similarly, when you change your speed, you rotate the direction of time – I have

  • another video explaining why.

  • But it looks like this: if every passing second I move to the left, then my clock will tick

  • like this.

  • And if every passing second you move to the right, then your clock will tike like this.

  • So when three seconds have passed on my clock, I'll measure only two seconds having passed

  • for you.

  • And yet when three seconds have passed on your clock, you'll measure only two seconds

  • having passed for me.

  • So we each think the other is measuring distances in time as shorter, but it's not a contradiction,

  • it's just how time behaves when it's rotated – it affects not just the passage of time, but

  • also our notions of "the same time" .

  • However, there's still an unanswered question: what if I stay on earth and you go off into

  • space and then come back?

  • Will one of us have actually aged more, or will we both have aged the same amount despite

  • constantly thinking the other was aging less?

  • This conundrum is called the Twins Paradox, and I'll explain the solution to it in my

  • next video.

  • But in the meanwhile, can you use rotating time to figure out why the twins paradox isn't

  • a paradox?

One of the most revolutionary things we learned in the 20th century was that time is not absolute

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ツインズパラドックス入門編(ローテーションTIME! (The Twins Paradox Primer (Rotating TIME!))

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    林宜悉 に公開 2021 年 01 月 14 日
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