## About the dimensions of the universe

A dot has no dimensions
A line has 1 dimension
A square has 2 dimensions
A cube has 3 dimensions
A tesseract has 4 dimensions
And time is another dimension just like those

In theory we can think of lines and squares, but we can't build them in the real world. If any of all the dimensions of an object is zero, then the object does not exist. For example:

If a square has 0 depth, it can't exist in the real world, or can't be built because even a atom has 3 dimensions. The same applies to time, because if a tridimensional object exists for 0 seconds, than it never existed.

(all above is what I understood, correct me if I'm wrong)

But what I really want to ask is:

If nothing can exist or be built in less than 3+1 dimensions, does that mean every object in the universe must occupy some space on all the other dimensions that exist?

For example, if our universe is described by 4+1 dimensions, and tesseracts can be real objects and be built somehow, then our bodies, cars, houses and anything we can build, must occupy some space on that fourth dimension, or they couldn't ever exist on our perceptible 3+1 dimensions. Because if the length of a body on the forth dimension was 0, it couldn't exist at all.

If that is true, than everything we see and touch must occupy some space on all other dimensions the universe has, even our own bodies. Does that mean there's a portion of our ourselves we can't see or perceive?
 Recognitions: Gold Member Science Advisor That is indeed one of the implications of higher dimensions. In most hyperdimensional models (M-Theory and the like), the higher dimensions are so sharply curved as to "close up" on themselves at scales too small to technically qualify as "existing," in the scientific sense. So, one could call these "virtual dimensions," just like virtual particles. If these extra dimensions do exist (and there is strong circumstantial evidence to support that they do), then all existing things must occupy them. In fact, even empty space must contain these extra dimensions.
 How does this relate to the notions of extended extra dimensions? I've read that some theories don't require 'closed up' dimensions, that we might live on a 3 dimensional brane in a higher dimensional universe. Is this more than conjecture? How would we tell the difference between this and having all dimensions curled up?

## About the dimensions of the universe

Sometimes physical models (like those of quantum gravity) will be calculated in 2+1 dimensions for simplification.
 Yes, I've seen that done. But the high level guys talk about multiple dimensions which may or may not be curled up. I just wonder how our universe would differ between the two. I will dig further ... just found out about ITunes courses on line, so I shall be getting smarter.