There are many consequences of quantum mechanics that are counter intuitive to the everyday laws of physics we are accustomed to. Particles can pass though barriers, exist in a superposition of states (more on this later), get entangled, just to name a few.
These strange consequences has led some to question, what do these oddities say about the fundamental structure of reality?
To be clear, once we begin to leave the arena at which true experiments are possible for verification, we enter the area of philosophy and not science. The many worlds interpretation falls into this category. However, in this article I want to explain the ideas behind the interpretation, and give you insight into why several great physicists believe it to be true.
Let's start with the topic of superposition...
The idea being that a quantum particle, such as an electron, can exist in more than one state at a time. Now this is not necessarily strange. I'll give you an example of an everyday object does this...
How about the velocity of a car or a plane? If we consider a plane traveling northeast, we can say the plane is traveling in both the north and east directions at the same time!!
(For those with some mathematical background, this object I am referring to is a vector in space. And in quantum mechanics, there is a state vector which describes how a system behaves).
Now here is where the quantum weirdness comes in...
In the plane example, we can measure how much the plane is traveling north and how much it is traveling east. It can be traveling 3 miles east for every 1 mile north.
In quantum mechanics, only one of these components can be measured. We prepare it into a superposition, but when we go to measure it, we say that the state vector "collapses" to one of these values. The superposition actually refers to the probability that we would measure each component.
Applying this to our plane example, our quantum plane would be prepared in a state such that 40% of the time, it would be traveling north. And 60% of the time, it would be traveling east, or any probability we would like to prescribe.
So the state vector collapses to one of the possibilities once we choose to measure. Well what happens to the other possible outcome?
This is where the many worlds interpretation comes in. It says that the other possible outcome DOES occur...in another "world" or universe. It says that each time a quantum mechanical state vector collapses, a new universe is created where the other outcome occurred. In essence, there could be infinite sets of me and you, each experiencing a different set of events.
However, until we can find a way to detect whether this other worlds exist or not, they will have to stay within the realm of philosophy.
It's still fun to think about though.