Many Parallel Worlds
In modern day quantum physics, there is a theory known as " the many worlds hypothesis." Quantum physics involves many interesting paradoxes having to do with the world of matter smaller than atoms - the world of the so-called elementary particles. Down at that level, reality is not supposed to be made of discrete bits of matter, but of almost unimaginable phenomena that are only clearly expressible in mathematical formulae. An elementary particle is not really a particle or even an ordinary thing at all, but something called a "probability function." Though the idea is pretty abstract, physicists have made various attempts to explain this reality in more or less ordinary terms. The only trouble is that when they do so, abandoning clear mathematics for ordinary language, the results are always completely paradoxical: you get pictures of worlds, supposed to be real, that are really quite strange. The "many worlds hypothesis" is one of these paradoxical attempts to understand the world of elementary particles in ordinary terms.
The particular state or condition of a particle - its position in space, how fast it is moving, when it is likely to change internally - is given by a formula called a "probability function." This formula tells you how likely it is - or how probable - that the particle is going to change in a particular way. Here's is analogy for layman. If I wake up in the morning and see that it is raining, there are several possibilities regarding what I might do. Either I won't go outside at all, or if I do I'll take an umbrella, or perhaps I'll forget my umbrella and go out anyway and get wet. These are three different possibilities of what will happen, given that I notice that it is raining. Now different "probabilities" can be assigned to each of these possibilities, regarding which one I am likely to take. A "probability" is a numerical value expressing the degree of likelihood that some particular thing is going to happen. The probability for each possibility would depend on who I am - whether I am a very busy person and have to go out even though it is raining, or a man or leisure and can afford not to go out at all: whether I am absent-minded and likely to forget my umbrella, or very practical and certain to remember it. So there are three possibilities, and the likelihood of any of them happening depends upon my personal characteristics. The analogy with an elementary particle is that my personal characteristics are like the possible states of the particle, and the likelihood of its changing in various ways would be expressed in the probability function. Now for the elementary particle, this function is all we know about the particle. This is what quantum physics tells us. Physicists like to say that the particle at the bottom is its probability function: it is the likelihood of its changing in either of its several possible ways.
When an event actually occurs - when the particle does in fact change - the probability function is said to "collapse," i.e., one of the possibilities is realized and the others at that moment seem to be eliminated. Something actually occurs. (Either I go outside, or I don't. I either forget my umbrella or I don't.) The other possibilities are now no longer possible, so we no longer have a probability function. We have a new fact. But since the physicists think that the reality of the new particle is its probability function, this new fact is just a new probability function, describing its current state and its new chances if changing into some other condition.
Now the question comes up, since all we know about the particle is it probability of changing - what happened to the possibilities that did not occur? Where did they go? Were they unreal to begin with? Well, for the physicists, one way of answering these questions is to assume that in fact they all occur, only they occur in parallel universes to the one in which we are making our physical observations! It is as if the moment that I observed that it was raining outside, three different universes sprang into being; in one I decided to stay at home and not go out; in one I went out and took my umbrella, and in a third I went out and, forgetting my umbrella, got soaked. Each of these three universes goes off on its own further journey, entirely separate and out of touch with the others. And in each of these new universes, a new set of possibilities opens up, a new probability function appears, which in turn will "collapse" as a new event occurs, so that the universe is continually splitting apart into new parallel universes every time a decision is made and a set of possibilities becomes a set of parallel realities.
Now this may sound very bizarre, but there are many physicists who believe that it truly describes the one in which we really live.
The particular state or condition of a particle - its position in space, how fast it is moving, when it is likely to change internally - is given by a formula called a "probability function." This formula tells you how likely it is - or how probable - that the particle is going to change in a particular way. Here's is analogy for layman. If I wake up in the morning and see that it is raining, there are several possibilities regarding what I might do. Either I won't go outside at all, or if I do I'll take an umbrella, or perhaps I'll forget my umbrella and go out anyway and get wet. These are three different possibilities of what will happen, given that I notice that it is raining. Now different "probabilities" can be assigned to each of these possibilities, regarding which one I am likely to take. A "probability" is a numerical value expressing the degree of likelihood that some particular thing is going to happen. The probability for each possibility would depend on who I am - whether I am a very busy person and have to go out even though it is raining, or a man or leisure and can afford not to go out at all: whether I am absent-minded and likely to forget my umbrella, or very practical and certain to remember it. So there are three possibilities, and the likelihood of any of them happening depends upon my personal characteristics. The analogy with an elementary particle is that my personal characteristics are like the possible states of the particle, and the likelihood of its changing in various ways would be expressed in the probability function. Now for the elementary particle, this function is all we know about the particle. This is what quantum physics tells us. Physicists like to say that the particle at the bottom is its probability function: it is the likelihood of its changing in either of its several possible ways.
When an event actually occurs - when the particle does in fact change - the probability function is said to "collapse," i.e., one of the possibilities is realized and the others at that moment seem to be eliminated. Something actually occurs. (Either I go outside, or I don't. I either forget my umbrella or I don't.) The other possibilities are now no longer possible, so we no longer have a probability function. We have a new fact. But since the physicists think that the reality of the new particle is its probability function, this new fact is just a new probability function, describing its current state and its new chances if changing into some other condition.
Now the question comes up, since all we know about the particle is it probability of changing - what happened to the possibilities that did not occur? Where did they go? Were they unreal to begin with? Well, for the physicists, one way of answering these questions is to assume that in fact they all occur, only they occur in parallel universes to the one in which we are making our physical observations! It is as if the moment that I observed that it was raining outside, three different universes sprang into being; in one I decided to stay at home and not go out; in one I went out and took my umbrella, and in a third I went out and, forgetting my umbrella, got soaked. Each of these three universes goes off on its own further journey, entirely separate and out of touch with the others. And in each of these new universes, a new set of possibilities opens up, a new probability function appears, which in turn will "collapse" as a new event occurs, so that the universe is continually splitting apart into new parallel universes every time a decision is made and a set of possibilities becomes a set of parallel realities.
Now this may sound very bizarre, but there are many physicists who believe that it truly describes the one in which we really live.
Do We Live in a Multiverse?
What came before the big bang? Maybe other big bangs. The uncertainty principle holds that even the vacuum of space have quantum energy fluctuations. Inflation theory says our universe from such a fluctuation- a random event that, odds are, had happened many times before. Our universe may be one in a sea of others just like ours - or nothing like ours. These other universes will very likely remain inaccessible to observation, their possibilities limited to our imaginations.
References
Hall, M., Deckert, D., & Wiseman, H. (2014). Quantum Phenomena Modeled by Interactions between Many Classical Worlds. Physical Review X, 4(4). http://dx.doi.org/10.1103/physrevx.4.041013
