Why does my GPS think my car has moved in the garage at night? Can humans survive a space-ride to Mars? Why are epsom salts worth their salt? What is a black hole and what is inside it? How do the equations for special relativity and kinetic energy relate? Why is Pluto where it is in the solar system? Why have right and left headphones? Join Dr Chris for this week's brain-stretching science phone-in on 702.