David Deutsch has written a book called The Fabric of Reality which constructs a unified theory of reality out of quantum physics, evolution, epistemology, and information theory. He picks up Hugh Everett's theory of a multiverse and runs with it. I'm impressed by his breadth of vision and the scope of his imagination, even though I disagree with his final outcome.
Metaphysics asks, "how many futures are there?" Deutsch offers a daring answer--all possible futures exist.
Deutsch's multiverse model has some attractive features. It provides a satisfying solution to the questions raised by the Intelligent Design movement. Intelligent Design argues that biological systems contain features that cannot be explained on the basis of mere time and chance. Deutsch provides infinitely more time and chance for evolution to play with--in his theory, the world we live in one of an uncountable infinity of parallel worlds. Not only does our improbable world exist, there are even greater improbabilities--worlds where monkeys type the text of Shakespeare. If it is physically possible, Deutsch says it exists.
Deutsch defines "physically possible" as "permitted by quantum physics," which means that all possible worlds exist. He envisions people playing quidditch in Harry Potter universes, where all the laws of physics still apply, but an endless string of improbabilities permits people to fly on brooms.
Deutsch is consistent about the implications of his theory--which tends to defeat his purpose. A Harry Potter universe just seems unthinkable. I'm not dismayed by the counter-intuitive nature of the concept, but there's more about Deutsch's model that makes it incompatible with humanity, whether or not it is scientifically sound.
Larry Niven's story "All the Myriad Ways" features police detective Gene Trimble sitting at his desk and considering the implications of an escalating wave of senseless crimes and suicides that started soon after the Crosstime ships started traveling to alternate parallel worlds. The story ends with Trimble sitting at his desk and considering the business end of his service revolver. As written, the story has ten different, parallel endings, representative of the essentially infinite number of endings possible under the Everett Interpretation.One of those endings, of course, is that Trimble pulls the trigger and kills himself--becoming just one more of the senseless suicides that started his investigation.
As physics goes, Deutsch's theory is mostly unobjectionable. Yet I don't see it catching on with the general public. It answers the question of "how we got here" but it tells us nothing (or way too much!) about where we are going.
If the general public believed what Deutsch says, I would predict a wave of senseless crimes and suicides--except among the "old-fashioned" religious believers who still clung to some outdated sense that there is a Higher Power who will hold them to account for their actions.
Deutsch's theory of multiversal quantum Darwinism, if it ever became widely accepted, could tempt so many people to kill themselves that the only people left to continue civilization would be fundamentalists who still believe in a God who punishes suicide.