First off, modern mathematics and physics have proved that the universe has no boundaries. A man with a telescope powerful enough would see the back of his head, and a bullet travelling fast enough from a gun would eventually come back and strike the same man (if there was nothing in the way, planets, stars, e.t.c)
So, to start off, let's imagine the one dimensional universe:
_____________ The line to the left is a one dimensional-universe (imagine the line had no width) A dot living on this can move only back and forth. In order for this universe to have NO BOUNDARIES, one must wrap it into a circle. In this way, the dot will move continuosly in a circle. The circle is a TWO-DIMENSIONAL SHAPE, yet a ONE-DIMENSIONAL universe is wrapped around it...continuing
Imagine a two dimension universe which is a plane "2-D rectangle with no height" A dot moving on it would invariably reach an edge...UNLESS...the plane is wrapped into a sphere. In this way, the dot will continue moving around, even if it moved north, south, east or west. The TWO-DIMENSIONAL SHAPE (plane) was wrapped around a THREE-DIMENSIONAL shape (sphere) Maybe you can see where I'm going with this.
Imagine a three dimensional universe, in which a man can move through X,Y,Z axes. However, there is an edge to this universe. Following the previous pattern, what Four Dimensional Shape can we wrap this sphere around, so that not only can you go forever left, right, forward, and backward, but also that you can move upwards and downwards continuosly too!? The human mind, I'm afraid, is not equipped with the necessary hardware to visualize this, nor is the brain, the heart, the lungs or anything. However, there may be something that is...
There are very few truly 2-D occurances in our universe. A paper is 3d and the drawing on the paper is 3d. However, take a shadow, for instance. If I shoot a beam of light at a person, the resulting shadow will be genuinely two dimensional. Now, if I shot light at a four dimensional object...would not the shadow be 3D. This, in my belief, can explain the phenomena of a ghost. Now, one may wonder, where is this 4D object that the ghost is a shadow of? Let's move on.
Since I cannot visualize the proportions of a 4D object, I will consider it as a sort of dimension that we are inside of. Or better yet, a dimension that is inside of us. Either one should suffice, since it really doesn't matter, as we can't really visualize this. Continuing...think about the "soul". Countless studies have rendered it unseeable, unhearable, untouchable...pretty much undetectable in most respects. Now, I am a faithful believer in God, but I believe that His word and the teachings of His Son directly intertwine with science, and that religion and science MUST compliment each other, with no exception. So...back to the "soul". I believe that the soul has been "infused" into each human, EACH ONE, both non-religious and religious. This soul is our only connection to the fourth dimension. Image it as a receptor and a broadcaster, continuosly relaying our thoughts to God and back again.
One of the many questions children ask is "how does God see everybody at once?" Many parents just say he is omniscient and omnipotent (of course in a child's terms), and I do not deny this. It could be possible that within the fourth dimension, one has complete "spectatorship" over everything. However, I do not believe God is restricted simply to the fourth dimension, He is not restricted to anything. What I do believe is that heaven is in this fourth dimension (and possibly Hell).
Back to ghosts...these ghosts could be the shadows of people in the fourth dimension. Much like a two dimensional shadow can make images like those shadow animals that one can make on a wall, a three dimensional shadow can be animated.
There are many supernatural phenomena, and I am certain they can all be explained with science. I belive that God lives in an even greater dimension, even in no dimensional at all, and he can flit between all the dimensions at will. I also believe that with this definition, "time" is NOT a dimension, and that it is just a sequence of events moving towards an END. The Earth and the universe are by most accounts billions of years old, and the Bible DOES NOT CONTRADICT THIS. THE ADDITION OF PEOPLE's ages cannot tell you the true age of the Earth, and Genesis does not give that impression if it is read closely.
I hope I didn't post this in the wrong place, and I hope that it is a sound theory.