Ok so last time you all joined me we talked about how all frames of reference are equally valid, im on plane thinking im still and the world is flying below me, you see my plane and think its moving fast and the astronaut thinks the whole world is rocketing around.
One proof of this concept is the astronaut training people do when they go up in a plane and it falls at the same speed of gravity, they become weightless from their point of view, we think they are falling really fast.
Ok so this concept makes sense except... it turns out light always travels at the same speed in a medium. So if you turn throw a ball on a train you see it going at 10 km and i see it going 20km because of the train speed. However if you turn on a flashlight we all measure it going the same speed. And this creates issues...
Ok imagine your on a train going 0.5m/s an hour and you turn on a flashlight so its hits the mirror 1 m away and bounce back and lets say light travels at 1m/s, so you count and its 1 second to hit the mirror, 1 second to come back, 2 second journey great!
Now I look at you and i also see light traveling at 1 m/s , unlike the ball that changes speed. Now as the light is traveling out the mirror is getting much furthur away and the light needs to catch the mirror, when it bounce back the mirror move towards it.
So lets step it through second by second.
1 second in, light has traveled 1 meter, mirror has traveled 0.5 m forwards, 1.5 m from where it started, so light has 0.5m to go and somewhere in that 2nd second it catchs the mirror and bounces back, one the way make the reverse happens the mirror rushs towards the light and it takes less then 1 second for it to come back.
Ok do this is all very wierd and what it acutely tells us is that two different people can observe the same thing and see two different results. In the train reference it take 1 second to hit the mirror and one second to come back. Myself watching from outside the train see it take between 1 to 2 seconds to hit the mirror and leas then 1 second to come back
... and the spooky thing is they are both right!
Ok sorry still not at time dilation but really need to prove why we can get different results for he same action depending on reference.
