Time for the physics student to weigh in.
I'll start with the side topic of pole shifts. They have happened before and will continue to happen. It happens about every half million years or so, (I could be off on the time frame, I am not a geophysist) and we are about 300,000 years over due. The biggest problems will be with navigation. Planes, ships, and migrating animals will have issues with that. The magnetic field deflects some types of radiation from the sun, so the earth’s temperature will rise and fall as it shifts (and increase the occurrence of skin cancer.) The only plus to any of this is that it’s a slow process, we won't notice any difference in our life times.
The parallel universe thing. I wouldn't worry about it too much. Models are used because they are the best fit for what we observe. They change a lot as more is learned. If any one knows anything about entropy, this was a huge worry at one time. Entropy basically says that all energy eventually is converted into an unusable form. Many physics believed that the universe would suffer a heat death, but now we know that isn't an issue. This sounds like one of those situations to me. The parallel universes out there doesn't necessarily mean there are other actual universes out there (although there could be) but that there existence fits the best mathematical models that we have.
All the theory and math for quantum mechanics is so wacky that we would throw it all away and start over if it wasn't for the fact that the math is such a good fit for what we observe. Mathmatical predictions for quantum mechanics are far more accurate than any other mathmatical models out there. They still aren't perfect and one day we might actually figure it all out.
