"All it takes is a grasp of theoretical physics, control of the space-time continuum, and maybe a ball of cosmic string.

...The more mass or energy you possess, the more the current around you varies. By moving at high velocity, for instance, you can make time slow down, and when you come to a stop, you'll be younger than if you'd remained at rest. Thus, a speedy spacecraft makes a fairly basic time machine...physicist Kip Thorne...suggested that a wormhole's entrances could be positioned in space and time as desired. Unlike some other time machines, this Thorne-inspired design allows round trips."

"To activate Thorne plates, the distance between each plate must be less than the width of an atom. The resulting wormhole will be equally small, so getting in and out might be difficult...In addition, Thorne believes that radiation effects created by gravitons, or particles of gravity, might fry you as you enter the wormhole."

"To take you back one year, the string must weigh about half as much as the Milky Way galaxy. You'll need a mighty big spaceship to make that rectangle."