Like how can time move slightly faster when i’m somewhere else? Also how, like in interstellar, a day on our planet was like 1,4 seconds on that one planet? I can’t seem to wrap my head around the concept of that…
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So time dilation and length contraction are two facts of the universe we just have to deal with. Another fact that we have to deal with is this: light travels at the same speed for any observer. So if you are sitting still and shine a torch, you see the photons flying away from you at the speed of light. If you are travelling 99% of the speed of light (LS), and you shine a torch forward, you will observe that the light still travels away from you at the speed of light. However, when you go talk to your friend who was stationary how fast the light came out of your torch, he will tell you that it travelled away from you at the speed of light. Not at your speed (99% LS) + LS, which would be 1.99× the speed of light. This is not allowed, according to current understanding of physics.
So one of the common ways to ‘visualize’ time dilation is the following thought experiement.
Consider you have a clock, and the way the clock works is a beam of light bounces up and down between two mirrors. Each bounce down and back up is 1 second. The light is travelling at the speed of light within the chamber of the clock. Now you and the clock start moving in a straight line. Now from your perspective, the light is still bouncing up and down once per second. However, your stationary friend sees that not only does the light have to travel up and down, it also has to move sideways to keep up with you. This means that the light in the chamber doesn’t travel the same distance, it travels a longer diagonal, and since its speed is constant, it must take more time to cover a longer distance. Let’s say from the point of your stationary friend, ths light takes 2 seconds to complete its path. [Here](https://youtu.be/hG_wUsqfHZs) is visualisation of what I’m talking about.
But how can that be? You see the beam ticking once per second, he sees it ticking once per 2 seconds. The only conclusion is that something is happening to your experience of the ticking of the clock. For you, time has remained the same, but from your friends perspective, your time has slowed down. The clock ticks slower.
This is not just a thought experiment. It’s been experimentally confirmed. It’s vital to account for this difference in [GPS satellites](https://www.astronomy.ohio-state.edu/pogge.1/Ast162/Unit5/gps.html). It’s also the reason why [we can detect muons from cosmic rays at ground level,](https://youtu.be/rVzDP8SMhPo), even though it seems like because of their extremely short lifespan they should all dissipate within a few km of reaching the atmosphere.
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