There are 3 forces that we know of that can be used to attract objects without "touching" them: electronic, magnetic, and gravitational. Electronic and magnetic forces can be adjusted so they REPEL things as well. It makes sense that gravity could be adjusted the same way. Perhaps the traveler does this to prevent diverting Earth's orbit. Maybe the traveler's ability to adjust gravity explains why gravity is the same on earth, the moon, mars, and Venus... Enjoyed your post! Been almost a year since I finished my chemistry degree so I don't get a chance to do these types of nerdy calculations anymore!