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
Imagine a really wide drag strip. Like one mile long and 5 miles wide. Two cars with identical top speeds take off from the start line one car goes straight ahead toward the finish and one car takes off at a 45 degree angle to the starting line. Who crosses the finish line first?
The car going straight forward only travels one mile, while the car at the 45 degree angle travels about 1.4 miles because trigonometry.
So even though speed is identical, the path you take matters.
So far so good, i hope.
Now, the cars with identical speeds are everything in the universe. You, me, photons, the forest moon Endor… everything moves at the speed of light. The drag strip represents spacetime. The fabric of the universe. Time is the forward direction, straight to the finish line. Space is the sideways direction.
Everything moves through space time at the speed of light. Some things move very little through space, so they travel straight ahead on the drag strip and move very quickly through time. Some things move very quickly through space (photons, cosmic rays, neutrinos) and hence move very little through time. These are like a drag car running almost sideways, parallel with the start line.
So, you jump in a space ship to move through space, and you end up experiencing less time, because your direction on the universal drag strip is now a little more in the space direction than it was when you were sitting still.
The real math is more complicated than this makes it sound, but i feel like this gives a good sense of what is going on.
Latest Answers