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
The best explanation for this that I’ve seen for people to get it is the train scenario. Think of it like this, there is a train going bye at the speed on light and you have a you see a passenger shine a light from floor to ceiling. To the passenger they just see the light shine up and the time traveled is short. The observer on the outside though sees the light travel at an angle with a length that is longer than the line to the ceiling. It basically takes a longer amount of time to see the light than it does for the passenger and that’s why time moves faster for the passenger or the observer slower than the passenger if you prefer.
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