Wormholes
What is a wormhole?  Well, before I begin to explain that, let me tell you of another substance, one so small, it is the same size as an atom to the -43 power.  (A^-43)  Basically, if you take the distance in size between Great Britain and an atom, that's the same difference in size as an atom is to this tiny substance: Quantum Foam.
   You can think of Quantum foam kind of like bubble wrap.  One piece of quantum foam (and there are almost infinite ones) is like one bubble.  And all those bubbles together flood the spaces between atoms.  Think of atoms as balls all wrapped together in bubble wrap -- quantum foam, that is.
   Now, in theory, each and every single bubble of quantum foam is a wormhole.  So: what is a wormhole?  Well, I like to think as wormholes as sort of like . . . hallways, or passageways in space.  Pretend that you have a 2-dimentional piece of paper representing space.  Now, if you pick two random points on the piece of paper, the shortest distance between them would be a straight line, right?  But wormholes can do something a little different: they can
bend space as if it were a two-dimentional piece of paper, and then connect the points, so the distance between the two points is much shorter.  Please look a the model below.
On the left is the original paper, and on the right, as you can see, the paper (space)  is being bend and a wormhole is formed between the two points.
In theory, the 'mouths' (or entrances) of the wormhole, as they are in the many dimentions of space, would be able to be moved and carried around.  However, there are a couple problems with this: because wormholes are very small, very unstable, and spend only an instant in existance before they disappear and are replaced, to open a single wormhole large enough for one person to go through on a one way trip, it would take anti-energy created by something the anti-matter size of Jupiter.
   Wormholes are also interesting because, as no one has ever created one, we do not know if they stay directly in this reality (see
Infinite Quantum Realities) or whether, when you went through, if you would come out the other end before, at the same time, or after you first entered.  We just don't know.  But if it works -- some time far in the future, wormholes could be a handy mode of transportation.