NOTES
Niven references pop up in the news pretty often – recently, astronaut Edward Lu suggested that an asteroid could be deflected by using the gravity of a space probe station-keeping nearby – the same method used in A World Out of Time to move the Earth itself. Advantages of this method include minimization of strain on the object being moved (it would be unfortunate to damage the Earth, or to break up the asteroid before it is safely past the Earth) – the only strain is the tidal force which can be made very small at the cost of lengthening the time needed to move the asteroid (or the Earth). This is obviously a method you can use only if you have a very long time to work with.