Time

While riding on a streetcar Einstein looked up at a clock tower and it all clicked.  Einstein realized that time is relative to where you are and how fast you're moving.  Time is the fourth dimension.  Bound tightly together with length, width, and depth, the dimensions of space. 

i.e.  If a person went on a 10 year journey at the speed of light (670Million miles/hour), 1000 years will have passed on earth.

If wormholes existed, they would be smaller than atoms.  If we want to go through them, it would take a tremendous amount of energy.  Not just ordinary energy, something called negative energy.  Negative energy is anti-gravitation.  It repels the fabric of space and time and would prevent gravity from crushing a wormhole.