I'm afraid I would have to disagree with the VERY esteemed Mr Hawking. You can't travel back in time by isolating an object and then making it go back through time.You must isolate the object from the universe and the make the universe go back in time.(Or at least the local area.ie the distance light travels in a year times the number of years you want to travel back in time. Apply the measurement you get to a spheres radius.That's a local area.) Somewhat energy intensive but works without paradox and violates no laws of physics.
