^Traveling to the past is impossible, even with Multiuniverses. There is about 1 universe for every nanosecond. I know this because every nanosecond something could change how your life ends up. Let me explain it through an example.
Let's say instead of going on Pokebeach today, you decide to go outside to walk around. Out there, you get shot and you die. Basically, there's going to be more than one universe/outcome. In one universe, you actually didn't go outside, therefore you never got shot and died. In another universe, you got shot, but you didn't die because you walked a little faster. In another universe, you decided to eat instead of going on Pokebeach or going outside. As you can see, there are billions of possibilities for just a little time. So basically, each second causes more universes to pop up, and from those universes more will pop up. (sorry if you don't understand this;I'm not the best explainer)
Now let's say you found out a way to get to these other universes. You still have to find the right universe out of like a quadrillion quadrillion quadrillion quadrillion to the quadrillionith power universes. Basically, by the time you found the right universe, you would be dead for like a trillion years.