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 speed of light (in vacuum) is constant, c.
If you turn on a LED while flying in your (vacuum) super plane at 0.99c and measure the speed of the light of the LED, the result has to be 1c.
Lets say your brother could also measure the light coming of your LED while hes still at the Airport. He will also measure the speed of the light to be 1c.
You are moving at 0.99C relative to your brother but you both measure the same speed. So something else must change in order to get the same result.
And that something is time. (And space, but lets focus on time) The flow of time will always adjust so lightspeed is exactly 1C no matter how fast you are.
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