World Building | Time travel, Multiverses, and the Endless Pain of Meta-Physics.

It only works on the worlds with specific characteristics. Hypothetically you could use another world's concept of time travel somewhere else, but that would mean testing each new world with every methods you have encountered. 

It also doesn't help that time travel doesn't affect those who travel the multiverse, which means if you paradox'd yourself into oblivion by accident, only Matthew or others like him will every remember.

The reason for this is how relative perceived time works. Say Person A travels the multiverse while Person B does not. Person B will be affected by time alterations on their world. But it Person A brings Person B with them, then Person B will also not be affected by time alterations. This principle also applies to objects.

Let me lay the ground rules of how traveling in a multiverse works:

1. A Traveler must have a clear enough idea of the world the want to go too.

2. The relative 'range' of where you are able to go is limited by entropic energy.

3. The more specific or wide the destination choices, the more power and time needed.

So if one plans to to world that is specifically just theirs but from two weeks ago, you'd drain yourself and will have to recharge and rest for a month or so. But if one wants to travel to an undefined fantasy world, then the power requirements are much more lenient and will take only a week for most to travel again.

For those who wish to go and, say, visit an exact previous version of themselves from a specific span of their life, then it would require world clusters worth of power in one go, or a hundreds of lifetimes worth of travel to even get the chance.