Springtime for Spacetime

Imagine you’re looking out onto a canal and see two insects on the surface of the water. Their weight presses down and causes a dip into which anything rolling on the surface could fall in towards them. This is how mass creates gravitational attraction by curving space-time – the bigger the insect, the larger the dip and the stronger the gravity. Now imagine the insects are moving about or spinning around. They can create small ripples on the water. Each ripple is like a small dip travelling out from the middle. Anything on the water’s surface the ripple passes under will be jiggled about, falling into the dips and pushed out by the peaks of the ripples. Space-time is a lot more rigid and the ripples a lot smaller, but it is that jiggling that missions like LISA are looking for.