First things first: don’t take this theory too seriously – it’s probably not going to happen. But I just had that thought and I wanna explain you guys, why I think, that Oden’s Wife was the former owner of the Yami Yami no Mi (or the Darkness-Darkness-Fruit).
1: What is the Yami Yami no Mi?
The Yami Yami no Mi is a devil fruit (obviously) that contains the power of darkness aka gravitation.
It is a logia type fruit, but unlike other logia fruits, the owner is not invincible to physical attacks (unless the attacker uses haki).
It was shown by Blackbeard, that he can create a Blackhole, that can draw any object with his infinite force of gravitation.
2: Why was Blackbeard looking for this fruit?
There is one thing, I ever wondered. It was stated, that Blackbeard read about this fruit in the illustrated referenced book.
It caught his attention and he knew, what power this fruit has. But to know, what power a fruit has, someone must have used it before and wrote it down – or someone saw the user of the fruit and wrote it down.
We don’t know anything about this devilfruit encyclopedia. Maybe it’s a neverending work, new fruits will be discovered and added in.
And maybe there was 20 years ago another user of this fruit..
3: What has Oden’s Wife to do with this fruit?
One Piece has gone scifi. With the recent chapter 919 we got the mindblowing information, that time travels are possible!
The main question is: HOW?
Leaving the Earth with an almost light-fast spaceship (relativistic velocities around 10% of the speed of light) and returning after a certain travel time has elapsed, a longer time has elapsed on Earth than on board the spaceship. The reason for this is the time dilation, which occurs according to the special theory of relativity of Albert Einstein at such high speeds. The exact course of such a time travel is described under twin paradox.
If the cruising speed and the acceleration are sufficiently high, an arbitrarily distant future for the traveler would be achievable, in principle, for the traveler in any length of time. However, for an acceleration that is reasonable for humans, a time lag of years also requires travel time of more than one year from the space crew’s point of view (in each case around 347 days for acceleration and deceleration at 9.81 m / s²).
So it is possible to go into the future..with a spaceship. Or is there another way?
Yes: The gravitation. Clocks move faster at the ground of the earth than at the top of the mountain. It’s also a point of the theory of relativity. That means, if the gravitation is higher, time moves faster. What place has the most gravitation? Excactly, a blackhole. It is pure mass, not even light can go through. A gravitation so high, that it would be possible to travel in time, if someone goes into this.
And what devil fruit has the power of gravitation? Exactly: the Yami Yami no Mi.
Conclusion:
Oden’s Wife was the former owner of the Yami Yami no Mi. She knew, how long it will take to make a gravitation field to send someone in the future. She knew, she had to die, so she made the prophecy, because she knew, that her gravitation field could send those people 20yrs in the future with her current lifespan.
After she died, the gravitation field got erased and those people in it, had traveled 20yrs into the future.
And after long years of search, Blackbeard found the fruit.
That’s it for today. Lot of speculation, lot of physics. I hope you like it.
*Theory by crate
