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 time spans you are dealing with are too short. Lets say you are going to Proxima Centauri. Which is 4.2465 light years away. Doing a round trip of 8.493 light years. You are travelling at 99.99999% the speed of light. For a round trip of about 8 years 180 days.
When you return. Your 20 year old brother who stayed on Earth will be 28 years 180 days old. As you were on the spacecraft. You’ll be about 20 years 14 days old.
Going around the earth once at .99C would mean something like 0.13 seconds for the observer and 0.018 seconds for the passenger.
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