And I also don't get your comment. Probably because I don't get relativity.
If we send a clock into space it will just tick away seconds (a unit designed by people). When it will return back to earth years later in my mind it just ticked away the same amount of time as it would have on earth.
What am I missing about relativity?
The track is divided into lanes and each player is set backwards based on their lane by a fixed distance, despite the fact the finish line is in the same position. This is because of the curvature of the track - if everyone started at the same "line" across all lanes, the runners at the outer lanes would be running a further distance than those on the inner lanes!
Gravity does the same thing to time itself. The curvature is not of a track but of spacetime.
In Gravity, the main character starts at an inner lane and his daughter at an outer one - but the starting line is the same across all lanes. Gravity bends spacetime, such that the inner lane is shorter than the outer lane (in terms of distance in time). So when they ultimately arrive at the finish line, the daughter has traversed a longer path in the time dimension than her father.
- https://www.youtube.com/watch?v=Bg9MVRQYmBQ
- https://www.youtube.com/watch?v=0iJZ_QGMLD0
(Although the time dilation in Interstellar is due to gravity, not high-speed travel.)
The classic example is a clock of light ticking between two mirrors. If you are moving with that clock it is ticking at the speed of light. If I am in a frame of reference where the clock is moving perpendicular to the light tick's path, the light will have a greater distance to cover. [1] Since the speed is fixed to me, this tick is slower.
1. https://upload.wikimedia.org/wikipedia/commons/thumb/8/8e/Ti...
Imagine the same volumetric difference exists in 3d space, but the different regions are not hotter/colder, but time goes faster/slower.
So You get two identical clocks, showing the same time, and move one of them into a “slow time” region (which would be a star moving very fast (8% of lightspeed). Let some time pass, then re-join the two clocks.
Since they spent some time in regions with different “speed of time” they’ll show a different time.
I might be wrong though, I’m not a professional.
So when you travel away from the earth at the speed of light you can't see the rotarion of the earth. But when you move back to the earth you are still just as old as the people who were the same age as you when you left?
Imagine your clock is an LED, a light sensor, and a mirror. The “tick” of this clock is: the LED sends out a brief flash of light, which travels to the mirror, bounces off, and returns to the sensor.
If this clock is stationary relative to you, the time of that tick is the distance between the three components divided by the speed of light (c = d / t).
If it is moving relative to you, the light has to be at an angle, shining at where the mirror will be by the time the light gets there. This is a longer distance, and so it ticks more slowly from your perspective.
Every atom in your body, or in a clock, is held together by forces that behave like the light in the example clock.
Give two people clocks and have them move relative to each other, and both think the other is slow. This leads to the “twins paradox”, and while I can say the answer involves acceleration, I don’t fully intuit it and can’t help you with it.