First of all, sorry to mislead all of you with this update. This is not a chapter. I'm busy today and won't be uploading a full sized chapter, so i thought i'd make use of what little free time to explain the whole time dilation thing.
What you need to know is that time does not move at the same speed for everyone. If you move faster, time slows down for you. Imagine the flash running around and doing things in his superspeed. to him, everything will be like a standstill, where time seems to move so slowly. everybody's 1 second might be an hour for him. so an object's velocity decides how fast it experiences time.
another factor is gravity, where the greater the gravity well you are in, the slower time passes as well. like with the Flash, 1 second in a greater gravity well might be an hour in deep space without the influence of gravity.
The 24 hour and 48 hour days of earth and Aioa are not dependent on the time dilation. it just means that Aioa rotates about its axis twice as slow as earth, hence each day is longer. However, Aioa experiences time at 7 times the speed of earth, due to the difference in locations within the universe and the difference in gravity they experience from their respective suns and supermassive blackholes in their galaxy. Hence, 1 hour on earth is 7 hours on Aioa.
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The colony ship though is travelling at a 0.57 the speed of light, so in a way, the 700+ years it had been travelling would only amount to a fraction of that on earth, since the instruments use to measure it's own time is also travelling at the same speed.
Finally, I know you all are confused about why centuries had passed on earth when Kiefer had only spent over a year on Aioa. I had intended to explain it in the end of Arc4, but that is still a long way to go, so I'll just do it now. When Kiefer died, he was sent to the netherworld, where Grandu extracted his soul and summoned it on Aioa much like an undead, but instead, Kiefer was reconstructed as a fully functional human being. The time he spent in the netherworld though, might have only been a few seconds. But because of time dilation between the netherworld and the other planes of existence, centuries had passed on earth and decades on Aioa.
Hence, he now arrives at the post apocalyptic world of Earth and the medieval ages in Aioa.
I might be wrong on some of the physics with the time dilation, im not too sure. this is basically what i understood from reading books. If it is indeed wrong, please point it out and i will correct it to the best of my abilities.