Is the Universe all that there is?

Many times has the history of our Universe appeared on this blog. However, what exists outside our Universe, and what is the true meaning of infinity? Many theories exist. Some think that our Universe is the only Universe and that it is infinite, while others support the idea of a Multiverse. A Multiverse is the infinite set of Universes. The Multiverse is defined in many different ways.

The first theory, that the Universe is infinite, is clearly impossible if the Big Bang is to be believed. Personally, I find it hard to believe that an infinite Universe could come from a Universe that, at one point, definitely had finite space. Also, due to the Planck constant, infinitely small isn't possible either.

As for the actual 'definition' of Multiverse, there is none. Some believe that all Universes are connected to ours, except we can't see them. I believe I can safely eliminate this possibility by using the same argument as before with the fact the infinite space cannot rise from finite space.

Of course, some say that there aren't any other Universes, and our Universe is all that there is, finite or infinite. If for a moment, this theory was to be believed, questions would arise. Such as "If our Universe is the only Universe, than where did the matter now in this Universe originate?" Again, short of saying the matter was merely floating around in a vacuum, the only explanation is that this Universe must have been preceded by another. Therefore the Big Bang is the Big Bounce. In my previous post "Black Holes and Universe Budding" I described the third main theory of the Multiverse. This theory is that, through black holes and Big Bounces, all current Universes (including our own) are descended from some "ancestor Universe". This theory is based on the possibility that the very physical laws of a Universe are random. For example, Universe A with 3 spacial dimensions, like ours, spawns a Universe B through a Big Bounce, which has 5 spacial dimensions. Still others, take the Darwinian approach and say that Universes have there own set of cosmological 'genes', which determine the physical characteristics of that Universe. In this theory, some of these 'genes' are passed on to the next Universe. This theory may seem unlikely, but little is known about anything on a Multiuniversial scale.

Another theory is called "bubble universes". This theory is also, like the previous theory, based on the fact that all current Universes are descended form an "ancestor universe". However, instead of black holes and Big Bounces, a "patch" of space expands into a Universe, independent of its parent. Let's call the ancestor Universe A. If this theory is to be believed, all Universes are 'inside' Universe A. Our Universe could be a sphere floating in the sky of another Universe, but to us our Universe is huge. Size is perspective and probably not constant to all Universes.

The final theory is more radical than all the others. Some think that there are infinite Universes in the Multiverse which suggests the true existence of infinity in space. This single idea turns many away from this theory, but it gets even better. The infinite Universes are determined by possibilities of other Universes. Let me explain. For example, a random person named Bob, is purchasing an ice cream cone. He cannot choose between vanilla and chocolate ice cream. Finally, in our Universe, he decides vanilla. However, another Universe is created at this precise moment, and in that Universe, he buys chocolate. In yet another Universe, he may realize that he has no money in his wallet, or possibly he chooses chocolate, but there is none left. As you can see, many possible Universes can exist just because of Bob's simple decision. The idea of the theory is that somehow, a Universe is created for each and every decision or possible outcome in any situation in any Universe. If we accept this fact, we can clearly see that an infinite set of Universes can result from all the situations in the past 13 billion years. In fact, even Bob's simple decision can lead to an infinite set of Universes because anything could happen at that exact moment, however improbable (e.g. a meteor hitting the ice cream shop).

An interesting variation of this theory is the possibility that the alternate Universes are "already there". In the infinite set of Universes, there is another Universe that is exactly the same, save that one detail. Let me return to my Bob ice cream example. When Bob purchases the ice cream, our Universe comes "in contact" with our Universe (note that the closeness isn't in physical terms. It is actually close in a sense that the Universes are very closely related when the same situation occurred in both of them, with differing outcomes).

Personally, I think that the reality is a combination of the theories mentioned above. My theory is there was one Universe in the beginning and that the Universes branch every time two possible outcomes come about. However, there is a catch, which I stumbled upon, but picked myself up shortly afterward. Bob gets vanilla one day, and chocolate on another branch of the Universes. However, in both Universes, he gets vanilla again the next day. Do the branches combine for this situation? However, the fact that he chose differently yesterday will change the situation of the next day very slightly, and therefore they will still be distinct. As for whether black holes "bud off" and become new Universes, I think that they do. I think this holds with my theory. Let us step back for a moment. According to my theory, all Universes branch at the time that a situation comes about, such as Bob's. Each of these outcomes has its own "path" on the tree of time. When a Universe buds off from a parent, both Universes are still on the same path, because they are connected physically rather than by an ancestry further back toward the "root" of the "tree".

Not much absolute information is known on this topic and for more info, see here and here.