I stopped reading "science"-fiction books a long time ago.
After you learn how fake our science is, and the real world it was hiding... well, the premise of this book just sounds dumb.
Its like a book on a group figuring out how to travel faster than the speed of light... when you know that the theory of relativity is complete rubbish.
There are tons of alternative earths... and stepping between them is easy. In fact, we do it all the time.
But there is not "every earth you can imagine"
- a world where the dark ages didn't happen so we are more advanced doesn't exist
- an empty earth does not exist.
- a completely peaceful earth, utopia, does not exist.
The reason none of these exist is because of how the universe works.
Worlds are split when the soul wants to explore two (or more) possibilities.
And time, the past & the future, are irrelevant.
And a whole new earth isn't formed for each person's individual actions/choices. Most actions end up with everything much the same. You still went to sleep in the same bed at the same time even though you decided to walk home instead of drive.
Good luck in your other worlds. 'Our science' seems to have given us computers and the internet to communicate with as well as keeping us alive longer.
That's not science, that's engineering.
Engineers use magnets all the time.
But, ask a scientist to explain how magnets work...
The current "theory" uses unicorn particles.
Obviously it's pixies :)