Parallel universes

The multiverse is the sum of all universes that exist. Wait a minute - there is only one universe, the one we live in, right? Well, maybe; but there might be an infinite amount of parallel universes and alternate realitites out there. In fact, contemporary physics suggests that this is a real possibility, because the multiverse could explain some weird properties of quantum mechanics.

What is an alternate reality or a parallel universe? Remember when you made an important decision in your life - choosing your spouse, your profession, or something like that. In the multiverse, there's a parallel world where you met someone else or chose a completely different carreer. So "over there", you live in the same time and space, but some properties of your reality are slightly different (or even many of them completely different). But how could this be possible? How can the same thing at the same time at the same place have different properties?

The concept of alternate reality has been a subject of many science fiction movies. My favorite is Back to the Future. It is based on the idea that if you travel back in time and change the outcome of a decision point (Marty's father standing up against Biff), a parallel timeline (an alternate reality) splits off, where the consequences of the different decision outcome lead to different versions of the characters. In the alternate universe, George McFly is a confident writer of science fiction stories, and Biff washes his car.

In a four dimensional world, every point is uniquely defined by its location in space and time. Thus, four coordinates lead to exactly one version of an object. Contrarily, in a multiverse, there could be many or even an infinite amount of versions of the same object at the same time in the same space. So, in order to characterize a fife dimensional object, a fifth coordinate in a fifth dimension is needed.

Blogger Rob Bryanton explains the fifth dimension as a split of the linear timeline into different versions. He has produced an excellent movie visualizing higher dimensions.

All of you know the concept of 3D. For example, you may have watched Alice in Wonderland or Avatar in 3D. An object in space has three dimensions, length, width, and depth. During its existence, an object can move and thus change its three dimensional properties - its position in space, or its size. Thus, time is a fourth coordinate that determines an object. For example, my three-dimensional body is sitting on my couch in front of the tv right now - but on monday, my ass will be back at the office (well, actually, I'm revising this post on Monday in the office in the "other" now). The same object has different positions in space for different points in time.

Now, the question was, how can an object have different properties at the same time at the same place? Imagine flipping a coin. The coin flips through the air, changing its position in time and space, until it lands on your hand and shows tails. But in an alternate reality, it would have shown heads. The multiverse theory says that right here, right now, the coin shows tails, but at the same time, at the same place, it shows heads - in a parallel world. Every decision and every observation of the outcome of a decision point splits our current timeline in different parallel universes, each of which represents different outcomes for certain events. Accordingly, this exemplary coin is a five dimensional object, because its property (showing heads or tails) is determined by five coordinates: Its position in space, the point in time of observation, and the decision outcome you observe. The position of the coin in the continuum of all possible outcomes is the fifth coordinate, or the fifth dimension.