The symbol for infinity is similar to the number eight lying on its side; but the meaning of this symbol has had the best minds scratching their heads for centuries. Alas, there are no straight answers to the question of what infinity is. Infinity is an enigma and a contradiction. It is the largest number imaginable but it is not a number itself. Infinity is a concept; a construct in mathematics that we use to make sense of the universe we live in. Well mathematicians might have things all sewn up, with infinity being just the 'fiddle factor' they need to make their equations work; but what is the scientific view? Scientists, in particular astrophysicists, ask questions like, 'Is the number of stars infinite?', 'Does the universe have a finite volume or does it go on forever?
Well believe it or not, the jury is still out on both those questions. Basically this is one question. Whether the universe is 'flat' (never ending) or 'closed' (its bound are limited). There has been tentative evidence from a satellite launched way back in 2001 called the Wilkinson Microwave Anisotropy Probe (WMAP) that gives a clue. Measurements taken by the satellite of the Cosmic Background Radiation suggest that the universe is 'flat'. That indeed, it does go on for ever. However, by today's standards the data does not stand up to rigorous scientific scrutiny. Another more sensitive probe, the Max Planck Satellite, was launched earlier this year (May 2009), with ten times the sensitivity of the WMAP. The qualified answer to the question, when it comes, will deservedly be hailed as a triumph. However, are we not being a little parochial by thinking only of our little universe?
Recalling the lines from Horatio in Shakespeare's Hamlet, "There are more things in Heaven and Earth than man can dream of." This quote is very close to my heart because it is a good example of 'out of the box' thinking. The lines in effect say that some things are 'un-knowable' in our world; but that does not mean that we cannot acknowledge their existence. That 'hidden world' to us does exist. We just can't see it. It exists in other, higher dimensions.
We are all familiar with the three spacial dimensions of our world: height, length & width; and let us not forget 'time', yet another dimension, but not spacial. Einstein made an honest living by bringing all these together in the General Theory. His brilliant concept of 'space-time' fitted the bill and successfully described the universe. However, as you might expect. Things are just not that simple. There is more, a lot more.
To understand the 'more' we must first get a handle on what we already know about dimensions. Well we can imagine the first dimension if we think of an infinitely thin stiff wire with an infinitely small bead free to move on it. The bead can only move backwards and forwards on the wire in a straight line. The second dimension is similarly easy to grasp. Think of a square of infinitely thin cardboard, with our bead free to roam anywhere on it. The bead moves in two dimensions. The third dimension is similarly easy. Imagine the bead being placed in a box, and the box being rattled. The bead will now follow a path in three dimensions as it rebounds off the inner walls in random directions. I wish I could go on and help you imagine the bead in the fourth dimensional and so on, but that is just too difficult for us to imagine directly.
But all is not lost, using topology, the mathematics of surfaces and shapes, we can at least tentatively take a glimpse into the fourth dimension. Here is how. It is normal experience that if a light is shone on a 3D object, a 2D shadow is produced. By a similar analogy if a light in 4D space is shone on a 4D object, then a 3D shadow is produced. For shadow, read shape. In other words, we cannot directly see a 4D object, but we can see its shadow, a 3D shape in our dimension.
You can see an impressive example of this at La Grande Arche, Paris, which is an architectural interpretation of the 3D shadow of a cube existing in four-dimensional space. You can check out the photos of this amazing structure, La Grande Arche, on Google Images.
Now that we have cut our teeth on the basics of dimensions, we can take a giant leap of imagination. Let us consider that our universe may not be the only one! That's right. Just when we thought we were making progress, along comes something to send us to the back of the class. The current thinking by a number of eminent physicists suggests that there are many universes, each existing side by side, but in different dimensions. Hence the term 'multiverse' was born and is now in common use. The scenario is of an infinite sea of universes, each like a soap bubble blowing in the wind; and like soap bubbles, some of these universes 'pop' out of existence at the end of their lives. New universes are formed all the time by budding from existing older ones, and so it goes on ad infinitum.
By making meticulous observations and processing data with super-computers, physicists are finding out new truths every day. The hard thing to accept is that many of their apparently 'off the wall' theories stand up and explain things right down to the finest detail.