Have you ever seen the rotation of a hypercube? Here:
http://en.wikipedia.org/wiki/File:8-cell-simple.gif That includes a rotation through time too, because it is expanding and shrinking in size as it passes through the center, which indicates a movement in time because of the change that takes place over a certain amount of time. No we don't live in the 3rd dimension, or we wouldn't even have the concept of time. We would just indefinitely exist the exact same way. And it's not necessarily an extra line, more like an extra dimension of depth to a figure. As for what Quanta/Quantum particles are, here:
http://en.wikipedia.org/wiki/Quantum
In the 10th dimension, change occurs on the smallest levels, where practically anything can happen, but nothing can exist in it because there is too much antimatter in the dimension. Enormous changes to the dimension happen randomly. For example, if you could theoretically live in the 10th dimension, you could make yourself grow wings, or even alter how many dimensions of depth you have (from 3 to x dimensions).
Oh and by the way, a hypercube is 2 cubes connected at their every vertex, but from the inside, like this:
[Image: hypercube-gif-animation.gif]
This is also a hypercube rotating through time too, if you want to know. We do live in the 4th dimension alongside 4th dimension creatures too, but our eyes can only comprehend up to 3 dimensions. So if we somehow saw a 4th dimension creature, we would only be able to see parts of it because our eyes can only perceive 3 dimensions of the creature. Building upon this, for your information, every hypercube and its rotation that I've showed you so far is only the shadow of the actual thing, since no one can draw or even know what it looks like. It's shadow is 3-dimensional however, just like how our shadow has 2 dimensions. Because of that, we can draw the shadow, which is always a 3D drawing, because that's the only way it is. You cannot draw the cube inside the cube correctly without 3 different dimensions to work with. To explain these concepts better:
http://www.youtube.com/watch?v=UnURElCzGc0
RIP Carl Sagan, you left a great legacy behind to us.
"In many ways, the work of a critic is easy. We risk very little, yet enjoy a position over those who offer up their work and their selves to our judgment. We thrive on negative criticism, which is fun to write and to read. But the bitter truth we critics must face, is that in the grand scheme of things, the average piece of junk is probably more meaningful than our criticism designating it so. But there are times when a critic truly risks something, and that is in the discovery and defense of the new. The world is often unkind to new talent, new creations. The new needs friends. Last night, I experienced something new: an extraordinary meal from a singularly unexpected source. To say that both the meal and its maker have challenged my preconceptions about fine cooking is a gross understatement. They have rocked me to my core. In the past, I have made no secret of my disdain for Chef Gusteau's famous motto, "Anyone can cook." But I realize, only now do I truly understand what he meant. Not everyone can become a great artist; but a great artist can come from anywhere."
-Anton Ego/Peter O'Toole (1932-2013)