Asked by: Mike Gormally, Ireland
For all the talk about science being on the brink of finding the Theory of Everything, there's a host of everyday phenomena that have yet to be fully explained. For example, physicists have yet to solve the mystery of whether time really exists or is just a convenient illusion, while anthropologists still aren't sure why humans walk upright. But the most common phenomenon that still defies scientific explanation is inertia: the notorious property of all mass that makes it reluctant to respond to forces. As Galileo allegedly demonstrated by dropping things off the Leaning Tower of Pisa, all objects fall under gravity at the same rate - in flat contradiction to common sense, which says heavier objects should hit the ground first. The reason common sense is wrong is that the strength with which gravity attracts objects is precisely cancelled out by their reluctance to respond to gravity - in other words, by their inertia. But, to this day, nobody knows why this coincidence holds true - or, for that matter, why objects even possess the odd property called inertia. One thing's for certain, though: life would be a lot easier without it.
Robert is a science writer and visiting professor of science at Aston University.