In this thought experiment, my twin brother and I are both turning 20 at the airport.
At midnight on our birthday, we are both exactly age 20 years.
He stays put while I get on a 777 and fly around the world. The flight takes me 24 hours and so he waits 24 hours. I arrive and we are both age 20 years plus 24 hours.
If I instead get on an SR-71 and fly around the world at 3x speed of the 777, the flight takes me 8 hours so he waits 8 hours. I arrive and we are both age 20 years plus 8 hours. Clearly, we are both younger in this scenario than the first one.
If I got onto a super plane flying at 0.99x light speed and fly around the world, the flight takes me 1 second. Since I’m so fast, he should also only wait one second. Intuitively, I’m back and we’re both 20 years and 1 second old.
But my understanding of time dilation is that I’m 20 years and 1 second old when I’m back, but he would be much older since I was almost going at light speed.
Why is that? My flight and his wait time should both be much much shorter since I was flying much much faster.
In: Physics
He’s only 20 years and 1 second old. *You* are 20 years and 0.00001 second old. (Didn’t do the actual math, but you get the idea.) In fact, you’re a little bit younger in every scenario. A 777 or SR-71 just aren’t fast enough for it to be much of a difference.
As you go faster and faster, time for you goes slower and slower. To an outside observer, it’s as if each second takes longer and longer. Hence, time *dilation*. For your brother, you were travelling for a full second. To you, it was nearly instant.
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