I am not a physicist and I have to admit I don't fully understand the Many World's theory. My limited understanding is that it reconciles deterministic mathematics that underly physics with non-deterministic events such as atomic decay that are observed happening at the quantum level. As opposed to the previous Copenhagen interpretation of non-deterministic events is that those events exist in a state of flux, for example Shrodinger's cat is both alive and dead, until they are observed to be deterministic. The Many Worlds theory removes the dependency on the observer to say that all possibilities exist but we can only perceive one reality. Hugh Everret was the one who pioneered the idea by looking at what he termed Universal Wavefunction with Bryce DeWitt later coining the term "Many Worlds."
If you wan't to read a non-fiction book full of causality read, Isaac's Storm . It is about the 1900 storm and is full of personal stories that because of certain things happening led to many people's lives being changed forever due to the storm. It makes one wonder what the original cause is.
I totally agree with everything creating the future, even the smallest things. I've always found it an interesting concept, but never directly connected it to something so heavy from a small action on my part. Causality interests me so much that I even tolerate Ashton Kutcher in The Butterfly Effect. That and Back to the Future are two of the best films I know of that explore this thought.
Everytime I get pulled over by a cop and given a ticket, I always tell myself ...damn if I had just left 5 minutes earlier or later I probably would not have got that ticket. Then I remind myself that most days I don't get tickets and so I probably avoided them by having left or arrived 5 minutes later than I might have otherwise. This is an interesting topic but I quickly drive myself insane thinking about it ...so I try not to think about it. /reverb I AM THE MASTER OF MY OWN DESTINY. /end reverb
Off the top of my head I recall that string theory addresses the possibility of moving back in time that may be related to the Many Worlds theory but I don't know enough about either theory to say how closely they are related.
OT: A friend of mine collapsed and had a heart attack in my home this morning. Very scary. My wife lost it. Ambulance came and took him to the hospital. Looks like he will be OK for today, but he's had congestive heart failure for 10 years. This is the short version.
Glad to hear your friend is is OK. My grandma died from complications from congestive heart failure so I hope your friend gets better.