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ChampagneOnIce Sort of, but it is an interpretation of our single universe.
Quantum mechanics says that the best we can do when it comes to understanding nature is predict the probability of a measurement outcome being a certain value. For example, we cannot predict the precise location of a particle, just a probability cloud saying where it is most likely to be when we measure it. We do not know beforehand, until we measure. Then we know. Yet then it degrades into fuzziness again.
Although outcomes are uncertain, the probabilities are deterministic, and there is a precise mathematical formula to describe what these probabilities will be. It is called the "wave function". It is not a real wave like a water wave, just an abstraction. It is a complex number.
Picture each point in space and time having a 2-d plane attached to it, and inside the plane is a 2-d arrow. The arrow emanates from the point with a direction and length, and rotates, stretches, and contracts as one moves to other points in space and time. Sort of like a little analog clock at each point, rotating forward and back, speeding up or slowing down, yet also expanding and contracting in length.
When you square it's length, that gives you the probability of finding the particle there.
So probabilities are certain, yet specific outcomes are not.
One quirk is that you only get a specific outcome when you "measure" it. But the theory is not clear on what a "measurement" is. Many people have devised ways to interpret the wave function and measurement.
One interpretation says that there is one wave function for the entire universe, yet every time a measurement is made, the universe splits, or a new one buds off. Or each possible outcome is viewed as a separate bud. They all evolve on their own, yet with some "interference" that fades with time until they become more independent the further they get from the branch point.
The theory says that you live in only one branch, one path of outcomes. Yet supposedly the other branches exist in parallel realities, things that "could have been" according to your view, where you are stuck in your own version of reality.
I personally think it is nuts, since how can there be that many? Yet I am no expert.
I am reminded of Back to the Future where they break the timeline leading to alternate realities. Yet those movies are full of inconsistencies and paradoxes.
I personally think one can travel into the future (find a way to slow down your personal clock relative to the clocks around you, which special relativity allows!), but not the past. I think causal flow is fixed (causes preceed effects), at least on the scales of macroscopic objects.
Another problem is gravity. Einstein said it is the curvature of space, and we follow where it leads, yet masses warp space, too. It is deterministic, with no probability.
Nobody has yet found a testable theory to marry gravity with quantum reality!
