Alternate dimensions do exist IMHO.
However, the problem is how to get to one of them.
In a Popular Science magazine [or Discovery Magazine], there was an article on how Alternate Dimenstions or Parallel Universes exist.
It is possible that each parallel universe in the entire multiverse is so far apart that even if you do travel at the speed of light or faster, it might take you centuries to even reach your closest Alter Ego [other self].
Remember, our parallel universe contains more stars than all the gains of sand on Earth. Not only that, each star is about thousands and millions of light years apart from each other.
Not only that, the distance between the boundaries of two parallel universes can possibly be up to billions, trillions, or even quadrillions of light years apart.
So, do the math.
Like you said, anything you do or didn't do can effect the infinite worlds that parallels your world.
For example:
Let's say you were driving a Farrari in the middle of the night at high speeds. All of a sudden, you run a red light and another car hits you and you die.
Then, almost half [possible more] of your Alter Egos would probably do the same thing you did while the other would probably be acting more carefull when they drive at that same moment.
Or, some or a few might not drive at all while the remainder may drive at a later or earlier time.
As you are reading this post I have just made, my alter egos are probably doing the same thing but with some minor differences in the posts.
Just before I posted this message, I had to check my text before I posted it. I found out that I had to add a few more paragraphs or words to this post.
While I was tyoing this post, my alter ego was probably not careful on what he types on his post.
...!
