Parallel universes; the very words sound like the products of an overactive science fiction writer’s mind. Yet once again, it seems that nature holds no qualms about surprising us; Parallel universes are now a viable theory that may help us to understand any number of things, even including the birth of our own universe, and possibly its death.

Much of modern physics is concerned with effects that happen on the quantum scale; the size of things smaller than atoms, of particles that appear and disappear in fractions of a second, of things that can never be seen but underpin how our universe functions. Quantum mechanics is the science concerned with how this strange world operates.

It is intuitive for us to think in terms of three dimensions: up and down, left and right, back and forth. A Dimension is defined as a plane in or along which a body can move; for example, a tabletop would be a 2-dimensional space: a ball on the tabletop can move back and forth or left and right, but it cannot go up and leave the tabletop.

The 3 dimensional model of the world works well in everyday life, with the inclusion of another fundamental dimension: Time. Things move about in space, but whilst doing so they also move in time. Time as a dimension works exactly the same as space, except things are free to move in any direction in space but only one direction in time. However, in the quantum world, many of our best theories either lead to or require more dimensions to work. You may have heard of ‘String Theory’ as a model of quantum mechanics; it leads to 10 dimensions, and one of its derivatives, called M-Theory, leads to 11. Though the idea of impossibly small particles vibrating in 10-dimensions may sound a ridiculous concept, it is one possible model of quantum mechanics.

There is another quantum theory that leads directly to the idea of parallel universes; the sensibly named Many-Worlds Interpretation. Imagine this thought experiment: you stand at a fork in the road, and you can go either left or right. You choose to go right in this particular instance, or left; it matters not. However, what the Many-Worlds interpretation has to say that your choice of left and right caused our universe to duplicate itself. These universes are identical, except for in one you go left, and one you go right. Indeed, there is a universe in which you instead choose to turn around, one in which you pause to tie your shoelaces, and so on for any possible choice. Thus, there could be near infinite number of universes, a near infinite number of you.

The Many Worlds interpretation is only one model of quantum physics. Nonetheless, imagine the thought of millions of you, in uncountable other worlds, all engaged in very slightly different lives, changed by only one tiny choice. Are we unique? Only in our universe.